HomeMy WebLinkAboutCouncil Reading File - San Luis Obispo Creek Stormwater Resource Plan - External Review Draft
San Luis Obispo Creek Stormwater
Resource Plan
External Review Draft
June 9 , 2017
Prepared for the City of San Luis Obispo, Natural Resources
990 Palm St.
San Luis Obispo, CA 93401
Prepared by Stillwater Sciences, Inc.
895 Napa Avenue, Suite B -4
Morro Bay, CA 93442
EXECUTIVE SUMMARY
This report constitutes the San Luis Obispo Creek Watershed Stormwater Resource Plan (henceforth, the
“SRP”), whose overarching purpose is to develop strategies to best manage the risks and opportunities
presented by stormwater runoff from this coastal, mi xed-land-use watershed along California’s Central
Coast. This Resource Plan follows the guidance of the State Water Board in analyzing the San Luis Obispo
Creek watershed as a whole, integrating the current knowledge of the watershed and its receiving waters’
condition to guide recommendations for the multi -benefit management of stormwater to improve overall
watershed health.
The San Luis Obispo Creek w atershed drains approximately 84 square miles , with the City of San Luis
Obispo at its geographic center. The creek and its tributaries are used by south-central California
steelhead (Oncorhynchus mykiss, listed as “threatened” under the federal Endangered Species Act),
although only few areas remain with high -quality spawning and rearing habitat. Resource quality and
stream health decline monotonically down the channel network, with the most abrupt decline associated
with the urban center of the City of San Luis Obispo. Although a variety of direct channel impacts
coincide with this zone, the well-documented decline in various in -stream conditions through this area,
particularly water quality, is undoubtedly a primary result of urban stormwater runoff. Although potable
water is supplied almost exclusively from out -of-basin reservoirs, groundwater is used extensively for
agriculture and much of the watershed overlies a designated groundwater basin.
The protection or recovery of “w atershed processes ,” encompass ing the storage, movement, and delivery
of water, chemical constituents, and/o r sediment to receiving waters , should be the fundamental goal of
stormwater management, and this principle guides the analyses and recommendations of th is SRP. This
approach leads to multi -benefit outcomes because the focus is on correcting the underlying cause(s) of
resource degradation, not its variety of symptoms. Across areas displaying the greatest impacts to
resources, their clearest common ality is a loss of infiltration from the contributing watershed area. Thus,
the stormwater management strategies most responsive to this condition will be those that are most
effective at recovering this watershed process to the greatest benefit of all water resources .
In summary, using the guidance provided by the characterization of the watershed (Section 1), the lens of
impaired watershed processes (Section 3), and the identification of sites with the highest rating for
addressing those impaired processes through stormwater management (Sections 4 and 5), key areas and a
list of 19 potential projects sites have bee n identified that emphasize the types of structural stormwater
projects (r egional capital improvement projects , small- and large-scale low impact developmen t projects,
and green streets ) that are particularly amenable to addressing th e critical impairments to watershed
processes . Through coordination with other entities and the public in both the development (Section 2)
and implementation (Section 6) of th e SRP, this document details the methodology for developing its
findings and identifies multiple opportunities for multi -benefit watershed improvements.
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Table of Contents
EXECUTIVE SUMMARY ........................................................................................................................................................... 1
1 EXISTING CONDITIONS IN THE SAN LUIS OBISPO CREEK WATERSHED ............................................. 1
1.1 INTRODUCTION ..................................................................................................................................................... 1
1.2 THE SAN LUIS OBISPO CREEK WATERSHED ........................................................................................... 1
1.2.1 Watershed Setting and Boundaries ................................................................................................................ 1
1.2.2 Watershed Topography and Geology ........................................................................................................... 3
1.2.3 Stream Channels and Surface-Water Hydrography................................................................................. 5
1.2.4 Water Supply .......................................................................................................................................................10
1.2.5 Groundwater........................................................................................................................................................10
1.2.6 Land Cover ...........................................................................................................................................................14
1.3 RECEIVING WATER CONDITIONS ...............................................................................................................16
1.3.1 Habitat Structure ................................................................................................................................................17
1.3.2 Flow Regime ........................................................................................................................................................17
1.3.3 Water Quality ......................................................................................................................................................18
1.3.4 Energy Sources and Biotic Interactions.......................................................................................................22
1.3.5 Integrative Measures of Watershed Health ...............................................................................................22
1.4 IMPLICATIONS FOR STORMWATER MANAGEMENT .......................................................................25
1.4.1 Watershed Conditions and Pollution -Generating Activities ...............................................................25
1.4.2 Habitat Conditions.............................................................................................................................................25
1.4.3 Groundwater........................................................................................................................................................25
1.5 APPLICABLE PERMITS .......................................................................................................................................25
1.5.1 NPDES Phase 2 stormwater (MS4) permit.................................................................................................25
1.5.2 Pathogen TMDL ..................................................................................................................................................26
1.5.3 Nutrient TMDL ...................................................................................................................................................26
2 COORDINATION AND COLLABORATION IN PLAN DEVELOPMENT ..................................................27
2.1 PUBLIC ENGAGEMENT .....................................................................................................................................27
2.2 AGENCY AND COMMUNITY CONSULTATION ....................................................................................27
3 IDENTIFYING THE TYPES AND LOCATIONS OF PRIORITY PROJECTS .................................................28
3.1 PROCESS-BASED WATERSHED MANAGEMENT ..................................................................................28
3.1.1 Watershed Processes .........................................................................................................................................28
3.1.2 Watershed Management Zones of the San Luis Obispo Creek Watershed ....................................28
3.2 CONCEPTUAL PROJECT TYPES .....................................................................................................................30
4 CRITERIA FOR RANKING IDENTIFIED PROJECT TYPES ...............................................................................33
4.1 QUANTIFIABLE CRITERIA ...............................................................................................................................33
4.1.1 Areas of Importance for Groundwater Recharge ....................................................................................37
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4.1.2 Improved Access to High -Priority Steelhead Reaches ..........................................................................39
4.1.3 Flood Reduction and Water -Quality Improvements .............................................................................41
4.1.4 Opportunities for Integrated Benefits .........................................................................................................42
4.2 NON-QUANTIFIABLE CRITERIA ...................................................................................................................44
4.2.1 A Framework for Assessing Non -Quantifiable Benefits .......................................................................44
4.2.2 Source Control of Pollutants as a Non-Quantifiable Benefit ...............................................................45
4.2.3 Application of Non -Quantifiable Benefits in the San Luis Obispo Creek Watershed.................45
4.3 PRIORITY NEEDS AND IDENTIFICATION OF STORMWATER CONTROL MEASURES .......46
4.4 MULTI-CRITERIA BENEFITS AND OPPORTUNITIES ...........................................................................48
5 SCREENING AND RANKING PROJECT OPPORTUNITIES IN THE WATERSHED ..............................49
5.1 PROJECT CATEGORIES ......................................................................................................................................49
5.1.1 Regional Capital Improvement Projects (CIPs)........................................................................................49
5.1.2 Parcel-Scale Low Impact Development (LID) Retrofits.........................................................................50
5.1.3 Parcel-Scale LID for New (Public -Agency) Construction .....................................................................50
5.1.4 Green Streets ........................................................................................................................................................50
5.2 GENERAL APPROACH FOR PROJECT SCREENING AND RANKING ..........................................51
5.3 CRITERIA FOR PROJECT SCREENING AND RANKING ......................................................................53
5.3.1 Criteria for Regional Capital Improvement Projects (CIPs).................................................................53
5.3.2 Criteria for Parcel-Scale Low Impact Development (LID) Retrofits..................................................54
5.3.3 Criteria for Parcel-Scale LID for New (Public -Agency) Construction ..............................................54
5.3.4 Criteria for Green Streets .................................................................................................................................55
5.4 RESULTS OF SCREENING AND RANKING ...............................................................................................56
5.4.1 Results for Regional Capital Improvement Projects (CIPs) .................................................................56
5.4.2 Results for Parcel -Scale Low Impact Development (LID) Retrofits ..................................................59
5.4.3 Results for Parcel -Scale LID for New (Public -Agency) Construction...............................................61
5.4.4 Results for Green Streets ..................................................................................................................................65
5.5 SUMMARY OF RESULTS ....................................................................................................................................67
6 PLAN IMPLEMENTATION ...........................................................................................................................................69
6.1 IMPLEMENTATION PLANS, PROGRAMS, AND PROJECTS ..............................................................69
6.1.1 City Processes ......................................................................................................................................................69
6.1.2 IRWMP...................................................................................................................................................................69
6.1.3 Decision Support Tools ....................................................................................................................................69
6.2 COMMUNITY PARTICIPATION .....................................................................................................................70
7 REFERENCES ......................................................................................................................................................................71
APPENDIX ............................................................................................................................................................................75
1
1 EXISTING CONDITIONS IN THE SAN LUIS OBISPO CREEK WATERSHED
1.1 INTRODUCTION
This report constitutes the San Luis Obispo Creek Watershed Stormw ater Resource Plan (henceforth in
this document , the “SRP”), whose overarching purpose is to develop strategies to best manage the
potential risks and opportunities presented by stormwater runoff from this coastal, mixed -land-use
watershed along California’s Central Coast. In the spirit of the State Wate r Board Guidelines for Storm
Water Resource Plans, the approach being used for this Resource Plan affirms that “The watershed
approach is essential to integrate storm water management with other basic aspects of aquatic resource
protection and overall water management including flood control, water supply, and habitat
conservation ” (California State Water Board, 2015, p. 13). Thus, this SRP considers the San Luis Obispo
Creek watershed as a whole, integrating the current knowledge of the watershed and its receiving waters’
quality and overall health .
Given a long history of prior study of the watershed, prior sources have been widely utilized in the
preparation of this SRP. Noteworthy among them are the Watershed Enhancement Plan (Land
Conservancy of San Luis Obispo County , 2002), the Waterway Management Plan (City of San Luis
Obispo, 2003), the Juvenile Steelhead Distribution and Population Estimate (Alley and Associates, 2008),
the Program Effectiveness Assessment and Improvement Plan (City of San Luis Ob ispo, 2015), The San
Luis Obispo County Instream Flow Assessment (Stillwater Sciences 2014), and the Percolation Zone
Study (Stillwater Sciences, 2015). This prior published information has been supplemented with field
visits in summer 2016; a variety of p ublically available data on topography, hydrography, geology, and
land cover; and previously compiled online data from 2 nd Nature, Inc., the City of San Luis Obispo
(henceforth, “the City”), the County of San Luis Obispo (henceforth, “the County”), and California
Polytechnic State University, San Luis Obispo (henceforth, “CalPoly”).
1.2 THE SAN LUIS OBISPO CREEK WATERSHED
1.2.1 Watershed Setting and Boundaries
The San Luis Obispo Creek w atershed drains approximately 84 square miles , with the City of San Luis
Obispo at its geographic center (Figure 1 -1). Four tributaries (Stenner Creek, Brizz olar a Creek, East Fork
San Luis Obispo Creek, and mainstem San Luis Obispo Creek) flow south and west out of the Santa Lucia
mountain range to converge within the City itself; the y are joined by the valley -bottom tributaries of
Prefumo Creek (flowing east out of the Los Osos Valley) and Davenport Creek (flowing west out of the
Edna Valley). Mainstem San Luis Obispo Creek leaves the broad, alluvial valley in which the City is
situat ed to the south through a narrow canyon that extends about six miles to the Pacific Ocean at t he
town of Avila Beach .
2
Figure 1-1. Index map of the San Luis Obispo Creek watershed.
3
1.2.2 Watershed Topography and Geology
The physiography of the watershed strongly expresses the underlying geological materials, and in turn
influences most aspects of surface-water flow, groundwater, and thus (ultimately) the management of
stormwater runoff. Broadly, the watershed comprises th ree sections: a central northwest -southeast
trending valley (Los Osos and Edna valleys), flanked to the southwest and northeast by bedrock uplands
(Irish Hills and Santa Lucia Range, respectively) (Figure 1 -2). Based on nearly a half-century of prior
geologic mapping (Dibblee 1974, 2004a-d, 2006a -c; Hall et al. 1979), the Santa Lucia Range to the northeast
is underlain primarily by older, uplifted metamorphic rocks, over 70 million years old and now a
sheared, jumbled collection of mixed rock types with com mon outcrops of serpentinite—a rock that
originated from below the earth’s crust and hydrothermally altered during its uplift towards the modern
ground surface. In surface exposures it displays a characteristic green hue, sufficiently distinctive and
wides pread to have been designated the official State Rock of California. It is typically unstable on steep
slopes, in part because its unusual mineral composition inhibits the growth of all but the most specially
adapted vegetation. As a result, landslides of all scales (from a few yards to many miles across) are
common in this terrane.
To the southwest, much younger sandstones and siltstones of the Squire, Pismo, and Monterey
Formations have been uplifted to altitudes locally above 1,000 feet since their mari ne deposition over the
last 15 million years to form the Irish Hills. Although these rocks would otherwise have isolated the San
Luis Obispo watershed from any direct access to the Pacific Ocean, ongoing erosion by the creek has cut a
narrow canyon through the ridgeline through which both San Luis Obispo Creek and US Highway 101
now traverse to connect the City with the coastline. The present location of lower San Luis Obispo Creek
likely predates uplift of these rocks, with stream erosion keeping pace with the rate of tectonic uplift to
maintain this corridor up through the present day. Somewhat more resistant rocks just upstream of the
coastline, or perhaps a more rapid rate of initial uplift t here, apparently blocked a direct path of the
channel to the Pa cific Ocean; thus, the channel turns parallel to the coast for over a mile before finally
discharging into the ocean at Avila Beach.
4
Figure 1-2. Generalized geology of the SLO Creek watershed. The inset map highlights the three sections of the
watershed described in the text. Geologic units and contacts compiled and generalized from Dibblee (2004a -d, 2006a -
c).
5
From a hydrologic and stormwater perspective, the most important segment of the wate rshed is its
middle one-third, comprising the lowland areas of Los Osos Valley, the land area of the City itself, and
the southeast -trending Edna Valley. Although Franciscan rocks almost certainly underlie this part of the
watershed at depth, it is present ly an alluvial valley filled with many tens to over a hundred feet of sand,
gravel, and silt deposited by the creeks flowing southwest off the Santa Lucia Range and northeast from
the Irish Hills (Boyle 1991, as cited in CDWR 2004). Near -surface soils show substantial variability in their
grain -size distribution and thus in their localized ability to infiltrate runoff or to transmit shallow
groundwater (or “interflow”); but the overall properties of the basin -filling sediments suggest that
opportunities to infiltrate surface runoff should be common, and the prospects for widespread
groundwater storage and recovery should be good. To a much less degree these conditions may locally
apply in the sedimentary rocks of the Irish Hills; and they are probably all -but absent altogether in the
metamorphic rocks forming the mountains to the northeast.
1.2.3 Stream Channels and Surface -Water Hydrography
The stream channel network of the watershed has a dual personality. The drainage density across the
mountainous areas is high , reflecting the limited ability of rainfall to infiltrate. Mapped channels are
commonly separated by no more than a few hundred yards, and the deeply crenulated topography
suggests that less permanent surface-water features are even more closely spaced. In the lowland Los
Osos and Edna valleys, however, channels are much more widely separated, commonly by one -half mile
or more, as subsurface flow supported by greater infiltration begins to dominate over surface
conveyance. This overall pattern is complicat ed through the urbanized portions of the City where
constructed stormwater channels, in the form of road ditches, gutters, and storm drainpipes , capture
urban runoff and create a n ew, dense, and largely separate surface-water drainage system. The intrinsic
properties of the watershed, however, remain well -expressed outside of developed areas, leaving a
pattern of infiltration -dominated hydrologic processes that suggest a template for future stormwater
management in keeping with the physical attributes of th e watershed.
The pattern of seasonally and perennially flowing channels broadly reflects the geologic and
physiographic framework of the watershed. As documented by Alley (2008) and Bennett (2015), and
broadly affirmed by summer 2016 observations and loca l knowledge (Figure 1-3), headwater channels are
typically dry through the summer as the shallow soil layers dry out and opportunities for discharge of
deep groundwater are virtually nonexistent. As drainage areas increase down the channel network,
sufficient flow collects to maintain perennial reaches of upper Stenner and San Luis Obispo Creeks. As
these channels enter the lowlands, however, most tend to lose water into the subsurface and again go dry,
expressing the hydrologic consequences of a deep uncon fined aquifer supplied by insufficient surface
flows to maintain a high water table and thus perennial flow. This pattern is also repeated in the eastern
tributaries (Davenport Creek and East Fork San Luis Obispo Creek).
6
Figure 1-3. Pattern of summertime dry, transitional, and perennial (i.e., wet) channels (data transcribed from
Bennett 2015).
7
There are a few noteworthy exceptions to this overall pattern. Both Stenner Creek and San Luis Obispo
Creek maintain perennial flow upstream of their confluence near Marsh Street and US 101 for more than
1.5 miles into the valley, despite flowing over the alluvial basin sediments. These perennial reaches pass
through the City’s downtown core, and their persistence suggests either a thin alluvi al cover over
shallow, impermeable Franciscan bedrock; a preponderance of artificially lined channels, isolating
surface flow from the underlying sediments; and /or some contribution from urban baseflow. Regardless
of the underlying causes for these perenni al reaches, however, the channel is again dry shortly
downstream of the Bianchi Lane overpass below the confluence, and it remains dry or nearly so until
contributions from Prefumo Creek and the Water Resource Recovery Facility , and shallowing bedrock
wher e the alluvial valley pinches out against the southwestern Irish Hills, again supports surface flows
throughout the year (Figure 1-4).
Figure 1-4. Two sample flow records from lower San Luis Obispo Creek and upper Stenner Creek (a rchival data
provided b y San Luis Obispo County ).
San Luis Obispo Creek (top) displays perennial flow, strongly seasonal variability, and a dramatic, 30 -
fold variation between annual maximum peaks in dry years (e.g., Water Year 1976) and wet years (e.g.,
Water Year 1978) (red arrows). The gage (since dest royed) was located about 4 miles downstream of the
southern City limits and 3.4 miles upstream of the Pacific Ocean.
Stenner Creek (bottom) shows similarly extreme variability in peak flows (compare the peak in Water
Year 1990 [1.2 cfs] with that o f the following year [416 cfs]), and also the seasonal drying that is present in
all but the wettest period of the early 1980’s.
8
Not surprisingly, fish use of the watershed, particularly by south-central California steelhead
(Oncorhynchus mykiss, listed as “threatened” under the federal Endangered Species Act), is highly
correlated with these patterns of surface water hydrology. Suitable steelhead spawning habitat occurs in
Brizzolara Creek, Stenner Creek downstream of the confluence with Brizzolara , upper San Luis Obispo
Creek in Cuesta Park, and middle San Luis Obispo Creek (Figure 1 -5). All of these reaches are within
portions of the creek that have suitable surface flows to support steelhead during winter and often into
the spring. Unfortunately, fish passage obstacles that occur within the watershed under existing
condition s reduce the ability of adult steelhead to access these areas (Figure 1-5). Despite these obstacles,
spawning of anadromous adults is observed within these areas when surface flows d uring infrequent
winter precipitation events are substantial enough to provide access.
Suitable steelhead juvenile rearing habitat occurs within lower Stenner Creek, upper San Luis Obispo
Creek from Cuesta Park downstream to Ellsford Park, and from the Mi ssion Plaza area downstream to
the Marsh Street overpass. These are all areas adjacent to suitable spawning habitat. However, surface
flows during spring and summer are presently nearly always insufficient to support suitable rearing, and
are often complet ely dry. The portions of San Luis Obispo Creek with sufficient surface flows to support
steelhead rearing occur downstream of the water treatment plant releases, where rearing habitat quality
is less suitable. Despite the lower quality of habitat, the mere existence of perennial flow in this lower San
Luis Obispo Creek reach supports a well -documented rearing population of steelhead juveniles, and
anadromous smolts are regularly observed.
The patterns of surface water presence/absence and steelhead persi stence in the San Luis Obispo Creek
watershed suggest several management opportunities. Addressing key passage barriers, measures to
protect the noted steelhead habitat in Stenner Creek and San Luis Obispo Creek from fine sediment, and
actions to project or enhance surface flows in Stenner Creek and upper San Luis Obispo Creek would all
provide direct benefits to the steelhead population.
9
Figure 1-5. Suitable steelhead habitat (blue lines), fish barriers (colored polygons) and priority habitat reaches in
good (green lines ; the four locations are highlighted by green arrows ) and degraded (red lines) conditions
throughout the San Luis Obispo Creek water shed. Source: California Department of Fish and Wildlife Passage
Assessment Database (https://nrm.dfg.ca.gov/PAD/Default.aspx).
10
1.2.4 Water Supply
The City is the sole water purveyor within the city limits, and presently all r esidential, commercial, and
industrial water in the City and environs is provided from off-site reservoirs lying well outside the
boundaries of the watershed (City of San Luis Obispo 2016). Thus, alternative approaches to stormwater
management have the pot ential only to affect the demand for non -potable uses, notably outdoor
irrigation, and only if the chosen management approaches can store runoff from the period when it
occurs (namely, the winter rainy season, when irrigation demand is lowest) into the sum mer. The most
feasible location for such storage is the underlying groundwater basin (see next section), a reservoir that
would preclude subsequent incidental landscape irrigation but which is a locally important source of
agricultural water needs.
Currently, the City obtains water from multiple sources: Salinas Reservoir (Santa Margarita Lake), Whale
Rock Reservoir, Nacimiento Reservoir, and recycled water from the City’s Water Resource Recovery
Facility. Groundwater has also been utilized in the past , with the most recent reported use for municipal
potable supply in 1990 (City of San Luis Obispo 2016). Current groundwater use includes one non -
potable well, and two irrigation wells for the municipal golf course.
1.2.5 Groundwater
The San Luis Obispo Valley Grou ndwater Basin is a state-designated basin that chiefly underlies the
lowland upper Los Osos and Edna valleys bisecting the watershed, which includes most of the City of
San Luis Obispo (Figure 1 -6). Its mapped boundaries coincide almost exactly with the ed ges of the
alluvial sediment exposed at the ground surface (see Figure 1 -2), and includes both the recent
(Quaternary) alluvial deposits and the slightly older (Pliocene) terrace deposits, of similar sedimentary
properties and origin, that outcrop to the east. The basin has recently been designated by the state as a
medium priority basin that, as required by the Sustainable Groundwater Management Act (SGMA), has
necessitated the formation of a Groundwater Sustainability Agency (GSA) for the sustainable
mana gement of the basin. The GSA for the San Luis Obispo Valley Groundwater Basin is presently
developing a Groundwater Sustainability Plan (GSP) to be adopted by January 31, 2022 that will “include
actions to ensure groundwater levels are stable over time, wa ter quality is not degraded, and the
groundwater basin is managed in a fair, cost -efficient, and sustainable manner for all of its years” (see
http://www.slocountywater.org/site/Water%20Resources/SGMA/slovalley/pdf/SGMA101 -Flyer -
20160920.pdf.).
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Figure 1-6. Boundaries of the San Luis Obispo Groundwater Basin, as designated by the California Department of
Water Resources (CDWR 2004), within the boundaries of the San Luis Obispo Creek watershed.
12
Data from the San Luis Obispo Valley groundwater basin spanning the late 20 th century were reported by
the California Department of Water Resources (CDWR 2004) and were summarized in several recent
studies (Stillwater Sciences 2014, 2015), and so the following background information is extracted directly
from those reports. The groundwater basin and its contributing watershed receive between 19 and 23
inches of rainfall annually (CDWR 2004 ). Groundwater is relatively shallow in this 50 - to 100 -ft -thick
unconfined aquifer (Boyle 1991, as cited in CDWR 2004 ). Groundwater levels reported from a well in
Edna Valley near Pismo Creek have fluctuated between 5 and 80 feet below ground surface between 1958
and 1983 (Well: USGS 351258120364501 031S013E19H001M). Another well in Edna Valley has exhibited a
decline from 19 to 46 feet below ground surface from October 2012 to April 2016 as a result of the recent
drought conditions (Well: CDWR CASGEM 352001N1206071W001).
Groundwater in the basin is recharged primarily by infiltration of precipitation on the valley, applied
irrigation water, and streamflow (Boyle 1991, as cited in CDWR 2004). Impervious surface cover across
much of the groundwater basin likely inhibits per colation throughout the urban areas, and the basin is
also considered to be in overdraft (CDWR 2003) due to over -pumping by agricultural, municipal, and
industrial extractions relative to current recharge. Municipal water supply for San Luis Obispo is also
provided by water imported from neighboring watersheds to the north and the Water Resource Recovery
Facility (SLOCFCWCD 2012), and t reated wastewater generated by the City of San Luis Obispo
supplements these supplies through irrigation of parks, schools, sports fields, and commercial centers.
In addition to these summarized basin wide data, contemporary records of water levels in three wells on
the CalPoly campus were made available for the present study and analyzed for both groundwater flow
direction an d general trends over time (Figure 1-7). Water levels fluctuate within years and between years
by 10 –15 feet in the two northern wells (MW -1 and MW -7), and by only a few feet in the southern well
(MW -4). Flow directions are north -to-south, reflecting prima ry recharge from water draining off of the
Santa Lucia Range together with points of discharge and extraction towards the center of the basin (see
Figure 1-7 A). There is a clear indication of systematically declining water levels in the two northern wells
(MW -1 and MW -7) over their respective periods of record, but attributing a cause for this trend is
complicated by a somewhat parallel reduction in rainfall volumes over this period, together with near -
uniformity of water levels in the southern well over th e same period (see Figure 1 -7B). At minimum,
these data suggest that the health of the groundwater basin, at least in this northern part, is not
improving over time, an important context given ongoing and potentially increasing demands into the
future.
13
Figure 1-7. (A) View of the northern edge of the San Luis Obispo Valley Groundwater Basin and the three CalPoly
groundwater monitoring wells used to evaluate flow directions and long -term trends in water levels, and (B) plotted
data from the three wells and 3-month (seasonal) rainfall totals (b). Long -term declines in the two northern wells
(MW -1 and MW -7) are evident, following a trend (dashed lines, color -coded to match legend) similar to that of
seasonal rainfall totals over the same period.
B.
A.
14
1.2.6 Land Cover
Classification of land cover (Figure 1 -8) made use of the National Land Cover Database of 2011 at 30 -
meter pixel resolution published by the Multi -Resolution Land Characteristics Consortium (Homer et al.
2012). To emphasize the broad categories most likely to influenc e stormwater behavior, and in particular
to promote (e.g., forested cover) or inhibit (e.g., impervious urban surfaces) the infiltration of
precipitation into the subsurface and overland flow , the mapped land cover types were grouped into six
generalized categories :
“Water” and “Wetlands” includes NLCD wetland categories 90 and 95;
“Grassland/Herbaceous” includes NLCD categories 21 (“Developed, Open Space”) and 71
(“Grassland/Herbaceous ”);
“Urban” includes NLCD categories 22 (“Developed, Low Intensity”), 23 (“Developed, Medium
Intensity”), and 24 (“Developed High Intensity”);
“Forested” includes NLCD categories 41 (“Deciduous Forest”), 42 (“Evergreen Forest”), and 43
(“Mixed Forest”);
“Agriculture” includes NLCD categories 81 (“Pasture/Hay”) and 82 (“Cultiva ted Crops”);
“Other” includes all other categories, particularly Barren Land (31) and Shrub/Scrub (52).
15
Figure 1-8. Generalized land-cover categories from the 2011 National Land Cover Database.
16
1.3 RECEIVING WATER CONDITIONS
Characterizing the “condition” or “health” of a stream, lake, or wetland can take many forms. Virtually
all studies have a particular impairment or endpoint in mind, be it an evaluation in the context of
regulatory standards for water quality, the enhancement of one or more target speci es, or the
identification of locations and types of prospective stream -improvement projects. Although these are all
potential focus areas for stormwater resource planning, a more comprehensive organizing framework is
useful to ensure that all of the key as pects of watershed health are at least acknowledged, recognizing
that data may be more abundant for some aspects than for others.
This report embraces the conceptual framework offered by Karr and Yoder (2004), which uses the
biological condition of organi sms as the indicator of overall stream or watershed “health” (Figure 1-9).
This framework explicitly links the human actions collectively termed “urbanization” with the resulting
biological condition, typically the primary end-point of concern and almost always its most sensitive.
Urbanization alters the landscape, inflicting stresses on stream biota through a set of water resource
features (habitat structure, flow regime, water quality, energy sources, and biotic interactions) that can
each be assessed. Meaningful analyses of a disturbed watershed, and ultimately s uccessful rehabilitation
of the impacted receiving waters of that watershed, require understanding the many stressors and their
interactions that link human actions to biotic changes (e.g., Grimm et al., 2000). Thus the following
discussion is organized around the five altered water resource features of Karr and Yoder (2004) and the
urban stressors that can affect them.
17
Figure 1-9. Conceptual model of the varied stressors resulting from human a ctions that alter stream biological
condition (Figure 1 of Booth et al. 2004; modified from Karr and Yoder 2004).
1.3.1 Habitat Structure
Substantial prior work has documented habitat conditions, particularly with respect to the life -history
needs of south -cent ral California steelhead (Oncorhynchus mykiss), throughout the San Luis Obispo
Creek watershed. Summaries in the 2002 Watershed Enhancement Plan include a shortage of deep pool
habitat as the primary habitat deficiency (Cleveland 1995), particularly along the mainstem above and
through the downtown area of the City, and beyond to the confluence with Prefumo Creek. These reaches
also lacked riffles, complex instream shelter, and gravel substrate. Farther upstream into the Santa Lucia
Range, habitat was sever ely lacking in instream shelter and pools. Overall, few of the habitat units (13%)
had any instream shelter and as much as 70% of the stream had no overhead canopy cover. Also reported
throughout the mainstem was a very high level of embeddedness, with 50 –100% of the channel substrate
covered with fine sediments (Land Conservancy of San Luis Obispo County 2002 , p. 19).
A variety of migration barriers for adult steelhead have also been identified by Cleveland (1995), Levine-
Fricke-Recon (1998), Payne (2004), California Department of Fish and Wildlife (CDFW ), and City staff (see
also Figure 1 -5). Although not directly related to issues of stormwater management, the abundance of
barriers poses a significant obstacle to recovering the full potential of the wate rshed and its instream
resources.
1.3.2 Flow Regime
Given the dearth of long-term flow data on San Luis Obispo Creek, historic conditions and more recent
alterations must largely be inferred by analogy to other, long -term flow monitoring sites around the
central coast of California, and by such characteriza tions that are available here (e.g., Figure 1 -4). A highly
variable hydrograph, with dramatic differences in intra - and inter -annual peak discharges, is anticipated
in this region regardless of the details of watershed land use or human alteration. The siz e of relatively
18
frequent, annual -to-decadal peak flows are likely to be increased somewhat by watershed urbanization,
but the magnitude of more extreme events will be much more strongly influenced by the vagaries of
climate and local weather patterns (Hawl ey and Bledsoe 2011, Booth et al. 2016).
Of potentially greater consequence are conditions on the other extreme of the hydrograph, namely the
period(s) of low or no flow in the channel. Given the strong association of perennial and ephemeral
channels with the underlying geology, particularly in areas upgradient of intensive human activity, these
conditions can be assumed to have an intrinsic, underlying cause that is independent of subsequent
disturbance. However, a variety of activities —particularly groun dwater pumping and impervious cover
over once-infiltrative soils —are well-known to influence the duration and extent of seasonal drying of
stream channels, and these factors are almost surely at play in this watershed as well.
Stillwater Sciences (2014) ev aluated instream flow requirements for a number of Central Coast
watersheds (including San Luis Obispo Creek) in an effort to determine: (1) what minimum level(s) of
flow are needed in spring and summer to support critical life stages of federally listed s outh -central
California steelhead (Oncorhynchus mykiss); and (2) which streams are meeting these levels. Sufficient data
were available to generate a robust relationship between watershed area and necessary instream flows, a
reasonable result insofar as th e minimum flow for providing suitable aquatic habitat should vary with
channel size (i.e., larger channels require more water to remain ‘wet”), and channel size generally scales
with watershed area:
For steelhead spring flow requirements,
Q = 0.049Adr + 0.31;
and for steelhead summer flow requirements,
Q = 0.012 Adr + 0.20,
where Adr is drainage area in square miles and Q is the estimated minimum flow requirement.
As examples, the minimum flows for the perennial reach of San Luis Obispo Creek where it enters the
lower canyon (43.5 mi 2) is 2.4 and 0.7 cubic feet per second (cfs) in spr ing and summer, respectively;
where the channel passes through downtown in the Creekwalk constructed channel (13.2 mi 2) the values
are 1.0 cfs (spring) and 0.4 cfs (summer).
These minimum values are typically exceeded in many of the perennial reaches of th e San Luis Obispo
Creek channel network; conversely, they are obviously not met at all where and when the channel goes
dry. Discriminating those reaches with an intrinsic propensity for drying from those where human
disturbance has reduced flows below crit ical levels is a task for later stages of this project, and which may
not be entirely possible prior to needing to identify potential flow -enhancement project locations. Even
without full information, however, the most promising areas for such action can b e inferred—they are
likely to be (1) stream segments where the other water resource features (water quality, physical habitat,
etc.) are good and so where correction of flow limitations could yield direct resource benefits; and (2)
stream segments immediat ely adjacent to perennial reaches of the channel, and thus where relatively
modest improvements could result in significant extension of the wetted channel network.
1.3.3 Water Quality
Water quality data have been collected for many years by a program coordinate d by the Central Coast
Regional Water Quality Control Board, with data collected at various intervals at various locations and
archived on internet -accessible databases. In particular, the Regional Board has issued two Total
Maximum Daily Load (TMDL) designations for San Luis Obispo Creek: one for nutrients (specifically,
nitrogen [see
19
http://www.waterboards.ca.gov/centralcoast/wat er_issues/programs/tmdl/docs/san_luis_obsipo/nutrient/
index.shtml]) and one for pathogens (see
http://www.waterboards.ca.gov/cen tralcoast/water_issues/programs/tmdl/docs/san_luis_obsipo/pathoge
n/index.shtml ). For nutrients, monitoring results throughout the watershed have demonstrated that the
pollutant is originating from the water reclamation plant and agricultural sources enteri ng the creek
primarily downstream of the City. It also shows some improvements over the decade of monitoring,
although further actions will still be needed to meet the TMDL target. For pathogens, the spatial pattern
suggests a much stronger contribution fr om the urban parts of the watershed, and with a trend over time
that does not yet suggest that corrective measures have been effective in the face of continued
urbanization (Figure 1 -10).
20
Figure 1-10. Water quality monitoring results for N-nitrogen (top graph) and pathogens (bottom graph) (reproduced
from
http://www.waterboards.ca.gov/centralcoast/water_issue s/programs/tmdl/docs/san_luis_obsipo/nutrient/slo_nut_tm
dl_prog_rpt2013.pdf and
http://www.waterboards.ca.gov/centralcoast/water_issues/programs/tmdl/docs/san_luis_obsipo/pathogen/slo_path_
prog_report_2013.pdf). Yellow circles on the map show the location of sampling sites.
21
Other data from the Central Coast Ambient Monitoring Program paint a consistent picture of the urban
influence on water quality. A year’s worth of monitoring data from 2015, summarized from two stations
(310SCN [upstream of the downtown area of the City] and 310SLV [downstream of the City]; see Figure
1 -10 for locations), show the clear signatu re of two common stormwater constituents of urban runoff:
dissolved copper and dissolved zinc (Figure 1 -11). Although the effects of copper specific to steelhead
have not been well documented, a variety of studies of the effect of copper on other salmonid species
(e.g., Hecht et al. 2007) indicate that biological effects are discernable at concentrations of no more than
about 2 parts per billion (micrograms per liter [μg/L]). Prior reports cited in Hecht et al. (2007) have found
that chronic concentrations of 12 –15 μg/L, similar to those found in San Luis Obispo Creek, are associated
with delays in migration, reduction in spawning, and death.
Figure 1-11. Monthly monitoring for copper and zinc, from locations shown in Figure 1-10: 310SCN is just upstream
of the City center, 310SLV is downstream. Note the change in y -axis scales between the two graphs.
22
The City has also conducted its own water quality studies over time, one of which evaluated the
correlation between dissolved oxygen (DO) and nitrogen (N) during a period of intensive monitoring in
the summer of 2010. This study found no statistically significant correlation between these two
parameters, although both DO an d the concentration of nitrate-nitrogen (NO3-N) increased in the
downstream direction —DO somewhat modestly, NO3-N rather substantially (City of San Luis Obispo
2010). A planning-level evaluation of the City’s stormwater program (City of San Luis Obispo 201 5)
further anticipated that pathogens, sediment, and trash would be the highest priority “pollutants of
concern ” for the program, given the existing TMDL for the former and relatively common incidence of
the latter two in urban drainage systems.
1.3.4 Energy Sources and Biotic Interactions
Although “energy sources” (i.e., the tropic structure of the food web that supports instream organisms)
and “biotic interactions” (including predation, invasive species, and population dynamics) are two of the
water resource features that are key components of stream and watershed health, there is little direct
information on either of them in the San Luis Obispo Creek watershed. Although they are clearly
influenced in a variety of ways by the interaction of human populations a nd urbanization with the stream
and its riparian zone, they are acknowledged here primarily in the interest of completeness but without
the expectation that such considerations will be a significant driver of stormwater management for
resource enhancement.
1.3.5 Integrative Measures of Watershed Health
Biota, an integrative measure of aquatic -system “health,” has been collected by a variety of studies. The
most comprehensive collection of biological data in the Central Coast Region is compiled and maintained
by s taff of the Regional Water Quality Control Board. It includes data collected as part of the state’s
Surface Water Ambient Monitoring Program (SWAMP) and other data developed by the Regional Board
as part of the Central Coast Ambient Monitoring Program (htt p://www.ccamp.org/).
In the San Luis Obispo Creek watershed, t wo mainstem stations and the tributaries of Stenner, Prefumo,
and Davenport creeks have been monitored for BMI data sporadically over the past decade, with two
years (2002 and 2003) particularly well-represented in all data sets. The farthest upstream station (Figure
1 -12), 310SLC in Cuesta Park (see Figure 1 -10 for location), lies above most development zones; ranching
does persist upstream of the station, and so this may serve as an indicator of conditions in response to
predominantly agricultural (but not residential) land uses. EPT taxa (Ephemeroptera = mayfly, Plecoptera
= stonefly, Trichoptera = caddisfly ) were 10 –13 in those two years of monitoring, with 7% intolerant taxa
(i.e., taxa that do not thrive in polluted or otherwise impacted waters) and 19 –22% tolerant taxa. During a
field visit in 2012 , aquatic worms (highly tolerant) but no EPT taxa were seen in a cursory examination. In
the center of the city on Stenner Creek (310SCN), the channel has been severely stabilized but some
habitat features have been constructed; EPT taxa were 2 –6 in the same two years, with 0 –1% intolerant
taxa and 33 –41% tolerant taxa. 2012 field observations showed very few individuals, but with less algae
than the upstream site and a single mayfly/stonefly. Below most of the urban development (310SLV), the
results were 0 –1 EPT taxa, 0% intoler ant taxa and 36 –50% tolerant taxa; in the field, the bed was
predominantly sand with heavy algae growth and no EPT taxa observed.
Conditions recover marginally at the BMI station near the mouth of the creek at the Pacific Ocean
(310SLB). It has shown relatively few EPT taxa (1 –6), low intolerant taxa (one sample at 22%, the others at
0%), and up to 35% tolerant taxa.
23
Figure 1-12. San Luis Obispo Creek, from its headwaters (ridgeline at extreme right in the GoogleEarth image)
downstream through the town of San Luis Obispo (the large urban area at left -center). BMI stations shown with red
pins, photo locations are red pins with black dot. Top two photos taken at th e upstream-most site (310SLC), with no
upstream urbanization but significant grazing. The lower left photo was taken in the center of town at site 310SCN;
the lower right photo was taken below most urbanization at site 310SLV. The distance from the upstrea m-most site
(310SLC) to the downstream-most site shown here (310SLV) is about 4 miles, the Pacific Ocean is an additional ~6
miles downstream.
IMGP4224 IMGP4226
IMGP4237 IMGP4240
24
These instream data have been integrated into the “California Stream Condition Index,” a single -valued
score for a given monitoring event at a specific location. As described in Rehm et al. (2015, p. 3), “The
California Stream Condition Index (CSCI) is a new statewide biological scoring tool that translates
complex data about benthic macroinvertebrates (BMIs) found l iving in a stream into an overall measure
of stream health ...The CSCI combines two separate types of indices, each of which provides unique
information about the biological condition at a stream: a multi -metric index (MMI) that measures
ecological structur e and function, and an observed-to-expected (O/E) index that measures taxonomic
completeness.”
Using the CSCI, multiple locations within the San Luis Obispo Creek watershed paint a consistent picture
of overall aquatic health. Sampling in 2003 shows a progressive downstream degradation in conditions
(Figure 1 -13), with the intervals showing the greatest change coinciding with the urban areas of the City
of San Luis Obispo.
Figure 1-13. Results from 2003 benthic macroinvertebrate sampling by the Central C oast Ambient Monitoring
Program (data plotted and downloaded from www.ccamp.org ). From upstream (upper right corner of the map) to
downstream (lower left of map), the station identifiers and their California Steam Cond itions Index (CSCI) scores are
as follows:
310CAW192 (SLO Creek above Reservoir Canyon Creek), 1.031 (“Excellent”)
310SLC (San Luis Obispo Creek at Cuesta Park), 0.829 (“Fair”)
310CE0276 (Stenner Creek), 0.796 (“Fair”)
310CE0724 (SLO Creek above Marsh Stre et), 0.763 (“Poor”)
310CE0308 (SLO Creek below Marsh Street), 0.695 (“Poor”)
25
Two additional stations farther downstream on the mainstem San Luis Obispo Creek were monitored in
2002–2006 for calculating the Southern California IBI, a prior integrative measu re of invertebrate health
(Ode et al. 2005); these results are consistent with those of the CSCI in showing a marked loss of stream
quality through the downtown area of the City, a condition that does not recover before reaching the
Pacific Ocean.
1.4 IMPLICATIONS FOR STORMWATER MANAGEMENT
1.4.1 Watershed Conditions and Pollution -Generating Activities
The existing conditions of the San Luis Obispo Creek watershed summarized in this report highlight
several key issues that have guided the further development of the SRP. The fundamental finding is that
r esource quality and stream health decline monotonically down the channel network, with the most
abrupt decline associated with the urban center of the City of San Luis Obispo. Although a variety of
direct channel impacts coincide with this zone, the well -documented decline in various in -stream
conditions through this area , particularly water quality, is undoubtedly a primary result of urban
stormwater runoff.
1.4.2 Habitat Conditions
Limited rearing habitat in San Luis Obispo Creek and its tributaries severely constrains available
locations for instream summertime occupation by an aquatic species of high concern, namely south -
central California steelhead, particularly given the extent of the channel network that does not mainta in
year -round flow. In the mainstem channels, these seasonally dry reaches largely coincide with geologic
conditions conducive to infiltration and thus to water -losing stream segments. Thus, intrinsic watershed
properties are likely a primary determinant on the spatial extent and seasonal duration of dry channels,
but these attributes are almost certainly influenced by local groundwater conditions as well.
1.4.3 Groundwater
The San Luis Obispo Valley Groundwater Basin was identified in the early 2000’s as being i n overdraft, a
condition that has worsened over the past decade. Impervious cover throughout the central part of the
basin associated with development in and around the City has reduced the rate of once -natural recharge
into the underlying aquifer, even as it has contributed to increases in the magnitude and flashiness of
peak flows in the stream channel itself.
1.5 APPLICABLE PERMITS
The City of San Luis Obispo is subject to three permits under the Clean Water Act : the National Pollutant
Discharge Elimination System (NPDES) Phase 2 municipal separate storm sewer system (MS4) permit ,
and two Total Daily Maximum Loads (TMDLs) for pathogens and for nutrients . CalPoly is subject to
Section F (“Non –Traditional Small MS4 Permittee Provisions ”) of the same NPDES MS4 p ermit. This SRP
is most directly responsive to, and guided by, requirements of the MS4 permit. It has somewhat less
relevance to the TMDLs, as described below.
1.5.1 NPDES Phase 2 stormwater (MS4) permit
The city is covered under the Phase II Small MS4 General P ermit (2013 -0001-DWQ), with an issue date of
February 5, 2013. This SRP is most directly relevant to Section E.12 of the NPDES permit, the Post
Construction Storm Water Management Program , and in particular section E.12.k, which requires
permittees to meet post -construction stormwater management requirements through understanding and
application of a watershed-process approach. As described more fully in Section 3 of this SRP, the
26
importance of key watershed processes are inferred from physical attributes o f the landscape, and their
protection is achieved through measures that are tailored to those physical attributes (and grouped into
“Watershed Management Zones” [WMZs ]). This SRP uses the prior mapping of WMZs as the foundation
of its analyses and recommen dations, and so the actions undertaken with its guidance should be fully
supportive of the NPDES requirements.
1.5.2 Pathogen TMDL
San Luis Obispo Creek was originally placed on the 303(d) list in 1996 when it was found that pathogen
levels exceeded levels for protection of the Water Contact Recreation (REC-1) beneficial use. In May 2016,
after collecting water quality data for 10 years without finding sufficient improvement, additional efforts
have been implemented to achieve better outcomes. They are based on t he results of DNA analyses,
which strongly suggest that avian sources (particularly roosting pigeons in the tunnels through which the
creek passes) are dominant, with less significant contributions from cows, domestic pets, and human
sources. Efforts to reduce these inputs include greater engagement with CalPoly and the County of SLO
for source reduction in the upper watershed, conducting land owner outreach and assistance to initiate a
riparian fencing program to limit livestock from getting into the creek system. The City has focused on a
suite of investigations in the downtown core , downstream of the tunnels where the pathogen levels
skyrocket. These include a variety of pigeon -abatement projects , drain inlet filter installations, and sewer
line inspections and upgrades, none of which are affected by or influence this SRP.
Of more direct relevance to meeting the goals of the TMDL is the management of surface runoff from the
urban surfaces of the City, particularly roadways, which are undoubtedly contribut ory to some degree to
the pathogen loadings in the creek. This SRP emphasizes those stormwater contr ol measures (herein
termed “SCMs ”, following NRC 2009), particularly those emphasizing infiltration , that should be well-
suited to the soils an d topography of the City proper and that are highly effective at reducing pathogen
loads. Although not a major source, the treatment of stormwater from these areas using the approaches
identified in the SRP should contribute to the attainment of TMDL objectives.
1.5.3 Nutrient TMDL
In contrast to the Pathogen TMDL, the nutrient TMDL for San Luis Obispo Creek is focused almost
entirely on discharges from the Water Resource Recovery Facility , which discharges to the creek at the
downstream limits of the city. As such, this SRP is not anticipated to make a significant contribution to
the attainment of TMDL objectives ; however, a significant upgrade to the facility will be completed in the
next few years to correct this water -quality problem .
27
2 COORDINATION AND COLLABORATION IN PLAN DEVELOPMENT
2.1 PUBLIC ENGAGEMENT
In a small city such as San Luis Obispo, public engagement is often most effective in combination with
the presentation and discussion of proposals and plans before electe d officials. This External Review
Draft of the SRP is scheduled to be presented to the City Council on July 5 , 2017 for a study session , with
the expectation that it may be adopt ed at th at time, in conjunction with the City ’s effort to re-envision the
currently named “Stormwater Program ” to be more inclusive of a multiple-benefit watershed approach.
As part of this process, th is external review draft is being made available for prior public and agency
review , following the normal schedule for Council Agenda Reports.
2.2 AGENCY AND COMMUNITY CONSULTATION
Multiple agencies and non -governmental organizations (NGOs) have been consulted in the preparation
of this plan. These include:
Central Coast Salmon Enhancement, Inc., a local NGO
Coastal San Luis Resource Conservation District
County of San Luis Obispo
San Luis CoastKeeper, a local NGO
The Central Coast Regional Water Board
The Low Impact Development Initiative (LIDI)
Two AmeriCorps fellows , engaged through the Local Government Commission
In addition, a va riety of City of San Luis Obispo units were consulted, particularly those with an
important future role in plan implementation. These include the Water Division (which is involved in
many water master planning activities like the Sustainable Groundwater Ma nagement Act effort,
recycled water expansion, the Water Resource Recovery Facility upgrade to investigate direct potable
injection ) and the Public Works Department , which is the lead department for the Capital Improvement
Plan (CIP) Program at the City. All the projects identified in the plan have been provided to them for
review and comment , and for future incorporation of LID features. CalPoly coordination with the
departments of Facilities and Campus Planning were also ongoing throughout plan developmen t.
28
3 IDENTIFYING THE TYPES AND LOCATIONS OF PRIORITY PROJECTS
3.1 PROCESS -BASED WATERSHED MANAGEMENT
3.1.1 Watershed Processes
“Watershed processes” is the term adopted by the Central Coast Regional Water Quality Control Board
to encompass the storage, movement, and delivery of water, chemical constituents, and/or sediment to
receiving waters. Their protection or recovery across the urban and urbanizing landscape of the region is
the fundamental goal of stormwater management, an d this principle guides the analyses and
recommendations of th is SRP. The association of watershed processes with particular attributes of the
landscape—specifically, the site geology, its hillslope gradient , and the type of receiving water (e.g., a
stream or a lake) to which they drain —provide the definition of ten unique “Watershed Management
Zones” (WMZs ) that identify both the critical attributes of the landscape from a watershed -process
perspective and the types of stormwater management that is necessa ry to protect those processes
(CCRWQCB 2013).
3.1.2 Watershed Management Zones of the San Luis Obispo Creek Watershed
The San Luis Obispo Creek watershed is physiographically and geologically diverse; every WMZ except
#’s 7 and 8 (which cover the steepest terrai n draining to wetlands, large rivers, or the marine nearshore) is
represented here. Inside of the City limits, WMZs 1, 3, 4, 6, 9, and 10 are present; outside of the City but
within the watershed boundaries, most of these are present as well, together with WMZs 2 and 5. The
descriptions of the WMZs , as summarized from CCRWQCB (2013) with specific applicability to the San
Luis Obispo watershed, are as follows:
WMZ 1. Drains to stream or to wetland; underlain by Quaternary and Late Tertiary deposits 0 -40%, and Early to
Mid-Tertiary sed. 0-10%
Attributes and Management Approach: This single WMZ includes almost two -thirds of the urban area of the
Region; it is defined by low-gradient deposits (Quaternary and Tertiary in age) together with the moderately
sloped areas of these younger deposits that drain to a stream or wetland. The dominant watershed processes in
this setting are infiltration into shallow and deeper soil layers; conversely, overland flow is localized and rare.
Management strategies should minimize overland flow and promote infiltration, particularly into deeper aqui fers
if overlying a groundwater basin in its recharge area, as is the case for much of the San Luis Obispo Creek
watershed.
WMZ 2. Drains to stream or to wetland; underlain by Early to Mid-Tertiary sed. 10-40%
Attributes and Management Approach: This WMZ is similar to #1 in both materials and watershed processes, but
groundwater recharge is anticipated to be less critical in these areas; thus, whereas management strategies need to
minimize overland flow as with WMZ#1, they need not emphasize groundwater r echarge as the chosen approach
to the same degree.
WMZ 3. Drains to stream or to wetland; underlain by Franciscan mélange and Pre -Quaternary crystalline 0-10%
Attributes and Management Approach: This WMZ includes those flat areas of the Region underlain b y old,
generally impervious rocks with minimal deep infiltration and so not overlying mapped groundwater basins.
Although relatively uncommon Region-wide, this WMZ is quite prevalent throughout the eastern part of the City
of San Luis Obispo. Overland flow is still uncommon over the surface soil; chemical and biological remediation of
runoff, reflecting the slow movement of infiltrated water within the upper soil layer, is the dominant watershed
process. Management strategies should promote treatment of run off through infiltration and/or filtration, and in
29
general by minimizing overland flow.
WMZ 4. Drains to lake, large river, or marine nearshore; underlain by all types 0 –10%, and Quaternary and Late
Tertiary deposits 10-40%
Attributes and Management Appro ach: This WMZ covers those areas geologically equivalent to WMZs 1 and 3
but draining to one of the receiving -water types that are not sensitive to changes in flow rates (in this watershed,
Laguna Lake). The dominant watershed processes in this low-gradient terrain are those providing chemical and
biological remediation of runoff. Virtually all of this area in the watershed also overlies the San Luis Obispo
groundwater basin and so also requires a specific focus on infiltrative management to support deep re charge into
the underlying aquifer.
WMZ 5. Drains to stream; underlain by Quaternary deposits, Late Tertiary deposits, and Early to Mid -Tertiary
sed. >40%
Attributes and Management Approach: These steep, geologically young, and generally infiltrative deposits are
critical to the natural delivery of sediment into the drainage system; management strategies should also maintain
the high degree of shallow infiltration that reflects the relatively permeable nature of these deposits, although
nowhere do they overlie a recognized groundwater basin.
WMZ 6. Drains to stream; underlain by Franciscan mélange and Pre -Quaternary crystalline rocks >40%
Attributes and Management Approach: In the San Luis Obispo Creek watershed, these steeply sloping geologic
deposits typically abut WMZ 9, differing only in their increased gradient. They are important to the natural
delivery of sediment into the drainage system but have little opportunity for deep infiltration, owing to the
physical properties of the underlying rock. Management strategies should maintain natural rates of sediment
delivery into natural watercourses but avoid any increase in overland flow beyond natural rates, which are low
where undisturbed even in this steep terrain.
WMZ 9. Drains to stream or wetland; underlain by Franciscan mélange and Pre -Quaternary crystalline rocks 10–
40%
Attributes and Management Approach: These moderately sloping, older rocks that drain to either a stream or
wetland are neither extremely sensitive to changes in infiltrative proce sses (because the underlying rock types are
typically impervious) nor key sources of sediment delivery (because slopes are only moderate in gradient). None
include an underlying groundwater basin, emphasizing the relative unimportance of supporting deep in filtration.
Overland flow is still uncommon over the surface soil, and so management strategies should apply reasonable
care to avoid gross changes in the distribution of runoff between surface and subsurface flow paths.
WMZ 10. Drains to lake and underlain by Pre-Quaternary crystalline rocks 10-40%
Attributes and Management Approach: In the San Lis Obispo Creek watershed, the one area of this WMZ is
equivalent to WMZ 9 but drains into a receiving water, Laguna Lake, that is insensitive to changes in runo ff rates.
It comprises moderately sloped areas that are not anticipated to be key sediment -delivery sources (by virtue of
hillslope gradient), draining into a lake that generally does not require natural rates of sediment delivery for its
continued health. The area itself of WMZ 10 does not overlie the groundwater basin, suggesting that a broad
management focus on deep infiltration is unwarranted.
These conditions a nd management approaches have been summarized by CCRWQCB (2013) as follows:
30
1 Overland flow avoidance, groundwater recharge / interflow, evapotranspiration
2 Overland flow avoidance / groundwater recharge, interflow, evapotranspiration
3 Chemical & bio transformations / overland flow avoidance, evapotranspiration
4 Chemical & bio transformations (*)/
5 Delivery of sediment / groundwater recharge, interflow, evapotranspiration
6 Delivery of sediment / avoidance of overland flow, evapotranspiration
7 Delivery of sediment / (*) [not present in San Luis Obispo Creek w’shed]
8 / groundwater recharge, interflow, evapotranspiration [not present in San Luis Obispo
Creek w’shed]
9 / overland flow avoidance, evapotranspiration
10 / (*) [not present in San Luis Obispo Creek w’shed]
Processes listed before the “/” = key watershed processes; of primary concern for protection;
should be subject to most stringent numerical criteria.
Processes listed after the “/” = watershed processes of less critical importance; could be subject to
less stringent numerical criteria.
(*) denotes areas that do not require protection of the process of groundwater recharge unless
underlain by a groundwater basin (may apply in WMZs 4, 7, and 10).
3.2 CONCEPTUAL PROJECT TYPES
A variety of sources listing the categories of stormwater control measures (SCMs ) have been published or
are under active development throughout California and nationwide. Some of the major categories (and
some recent local reference sources for their characterization and design) are:
Regional stor m water capture (San Mateo County 2016)
Green streets (http://centralcoastlidi.org/, San Mateo County 2016 , Ventura County 2016 )
LID retrofits (San Mateo County 2016)
Bioretention (http://centralcoastlidi.org/, Ventura County 2016 )
LID parking lots (http://centralcoastlidi.org/)
These and other SCMs have been compiled in a near -comprehensive fashion by the California
Stormwater Quality Association (CASQA) (Table 3 -1).
31
Table 3-1. Compilation of common SCM categorie s, emphasizing the suitability of particular
measures in the various WMZs found in the San Luis Obispo Creek watershed.
Stormwater Control Measure
(SCM)
Capture
and
Reuse
WMZs :
Any/All
Infiltration
Optimize for
WMZs 1, 2, 4, 5
Filtration 1
Optimize for
WMZs 3, 4
Bioretention (infiltration design) x x
Bioretention (filtration design) x
Porous Pavement (infiltration design) x x
Porous Pavement (filtration design) x
Capture/Reuse x *x
Vegetated Roofs x
Soil Amendments x x
Downspout Disconnection x x
Filter Strips x
Vegetated Swales x
Infiltration (Retention) Basins x x
Infiltration Trenches x x
Dry Wells x x
Dry Ponds
(Extended Detention Basins) x
Constructed Wetlands x
Wet Ponds x
Media Filters / Filter Basins x
Proprietary Devices x
Site planning and design (see Table 3-2 ) X X
* depends on design
1Many filtration SCMs can also result in substantial runoff reduction via infiltration or
evapotranspiration.
Modified from Table 14 of CASQA (2010, p. 57).
The last entry on Table 3 -1, “Site planning and design,” also provides opportunities for the
implementation of nonstructural SCMs (termed “BMPs” in the original table, reproduced below as Table
3 -2).
32
Table 3-2. Elements of site planning and design in the context of Low Impact Development
stormwater management.
Table 6 of CASQA (2010 , p. 41 ).
33
4 CRITERIA FOR RANKING IDENTIFIED PROJECT TYPES
4.1 QUANTIFIABLE CRITERIA
As stated in in the Guidelines (2015, p. 21), “Plans shall include a metrics -based and integrated evaluation
and analysis of multiple benefits to maximize water supply, water quality, flood management,
environmental, and other community benefits within the watershed. (Wat. Code, § 1056 2, subd.(b)(2).”
Table 3 of the Guidelines lists some examples of how these benefits might be quantified : these are
reproduced with modifications (Table 4 -1) to focus on opportunities and challenges specific to the City of
San Luis Obispo.
Table 4-1. Examples of how benefits from various SCMs might be quantified (modified from the
Guidelines, 2015).
Benefit Example Actions Example Metric Units
Water Quality
(for overall improvement in
urban water quality, and to
support achievement of
TMDLs for pathogens and
nitrogen)
Filtration SCMs
Protection or reestablishment
of natural buffers around
receiving waters
Pollutant Load Reduction
lbs/day, kg/day
Volume Treated
million gallons per day (mgd),
acre -feet per year (afy)
Water Supply
(through stormwater
infiltration, and/or runoff
capture and use
Infiltration SCMs
Runoff capture SCMs
Volume Infiltrated or
Captured
million gallons per day (mgd)
acre -feet per year (afy)
Flood Management
(through peak flow reduction)
Reducing runoff rates and/or
volumes through infiltration,
capture, and/or detention
Volume Infiltrated or
Captured
million gallons per day (mgd)
acre -feet per year (afy)
Flow Reduction
reduction in cfs
Environmental
(habitat improvement, low-flow
augmentation)
Riparian buffer protection or
enhancement
Infiltration/groundwater
recharge SCMs
Flow control SCMs
Buffer Expansion
acres, linear feet
Instream Flow Increases
length of channel affected, low-
flow barriers eliminated
Biological Improvements
California Stream Condition
Index
34
Community
Enhanced and/or created
recreational and public use
areas
Community involvement
through workshops
Public education to improve
on-site stormwater
management and source
control of pollutants
Size
number of residents served,
acres of open space
created/protected
For the City of San Luis Obispo, quantification is feasible for some but not all of these benefits . A
complete quantification of all benefits would require development of a hydrologic model of the entire
watershed, a task that is beyond the resources of a small municipality . However , a more focused effort
using unit -area factors and presumptions of pollutant generation and/or pollutant -removal efficiency has
recently been accomplished for the City (2ndNature 2016), an d that work is utilized throughout the
following section s of this SRP as appropriate. More broadly, quantification of benefits in this plan follows
the overarching guidance of the National Research Council (2009, p. 4):
“Flow and related parameters like impervious cover should be considered for use as
proxies for stormwater pollutant loading. These analogs for the traditional focus on the
“discharge” of “pollutants” have great potential…because they provide specific and
measurable targets, which at the sam e time they focus regulators on water degradation
resulting from the increased volume as well as increase pollutant loadings in
stormwater runoff.” (emphasis added)
Thus, the specific applications of quantified criteria, as summarized in Table 4-2 , is recommended for
evaluating individual sites and projects in watersheds with similar physical conditions and funding
constraints as those found here.
35
Table 4-2. Actions to improve watershed conditions, and metrics recommended to evaluate the suitability
and benefits from such actions in the San Luis Obispo Creek watershed.
Benefit
Potential actions in the
SLO Creek watershed
Metric units to apply in
the SLO Creek watershed
Water Quality
Infiltration SCMs
Filtration SCMs
Buffer protection around
receiving waters
Primary: Impervious area
treated (acres)
As feasible: Particulate load
reduction (tons/year)
As relevant: Protected
and/or revegetated buffers
(lineal ft)
Water Supply
(through stormwater
infiltration, and/or runoff
capture and use
Infiltration SCMs
Primary: Impervious
area treated (acres)
As feasible: Volume
infiltrated or captured (ac-
ft/yr)
Flood Management
(through peak-flow and/or
volume reduction)
Infiltration and/or detention
SCMs
Primary: Impervious
area treated (acres)
As feasible: Runoff volume
reduction (ac-ft/year)
Environmental
(habitat improvement, low-flow
augmentation)
Infiltration/groundwater
recharge SCMs
Flow control SCMs
Riparian buffer protection or
enhancement
Primary: Impervious
area treated (acres)
As relevant: Protected
and/or revegetated buffers
(lineal ft); Flow-impaired
channels affected (length of
channel plausibly affected)
Community
(quality of life)
Enhanced and/or created
recreational and public use
areas
Community involvement
through workshops
Public education to improve
on-site stormwater
management and source
control of pollutants
Primary: Open space area
created (acres)
As relevant/feasible:
Number/size of community
served and/or engaged
(count)
36
This SRP differs from most that have been prepared in California to date by virtue of the limited area that
it seeks to cover. The San Luis Obispo Creek watershed is sufficiently small, and the number and variety
of critical watershed area s sufficiently limited, t hat even the condensed numerical scoring system
presented in Table 4 -2 is largely unnecessary to readily identify the most important sites and projects to
pursue. The highest ranked projects (or prospective project locations) will , in general, be those that are
located on the landscape to achieve all of the potential benefit categories (i.e., water quality, water supply,
environmental, etc.). Thus a detailed ranking or weighting scheme is unnecessary , since these projects
will always rate most highly regardless of the detailed quantitative method used .
Where financial resources are sufficient to consider funding of lower -rated projects then more refined
criteria may be necessary, but this is not a realistic expectation from a city of 45,000 inh abitants. Thus, the
emphasis on ranking potential projects in this SRP focuses on those areas where all of the primary
benefits can be achieved (thus also satisfying the Guideline’s emphasis on “multiple benefits”); more
refined evaluations are applied onl y for those categories where the number of such “all -benefit” projects
is small.
In summary , t he framework for identifying priority areas in the San Luis Obispo watershed for
implementation of stormwater control measures is a combination of environmental, water quality, and
water quantity considerations. These considerations are listed below and presented in more detail in the
text and maps that follow:
#1. Opportunities for infiltration to increase groundwater recharge.
#2. Opportunities to improve fish access to, and improvement of, high -priority steelhead reaches.
#3. Opportunities to reduce d ownstream flooding (based on known flooding areas and modeled
flow contributions).
#4. Opportunities to improve water quality.
Each of these criteria could be quantified at every prospective site using the metrics summ arized in Table
4 -2; but for purposes of developing a list of prospective future projects based on quantifiable criteria, the
following analysis emphasizes the identification of sites that substantively address all of these
opportunities , by virtue of the watershed processes that they are able to protect or restore .
37
4.1.1 Areas of Importance for Groundwater Recharge
Figure 4-1. Watershed management zones and groundwater basins in the central part of the San Luis Obispo Creek
watershed, highlighting those areas where infiltration has a relatively greater likelihood of success for supporting
groundwater recharge.
38
Figure 4-1, which covers the City of San Luis Obispo, display s the distribution of WMZs and the
underlying groundwater basin. The close alignment of the basin with WMZs 1 and 4 affirm the interplay
of mapped surficial deposits with the presumed extent of significant groundwater resources.
Some disparities exist between the two mapped features, however. Where thes e two sets do not align
(particularly in the eastern part of the City , east of Broad Street ), recent explorations suggest that WMZ 1
may be less extensive than implied by the geologic mapping on which the WMZ determination was
made. Conversely, areas where the groundwater basin is mapped as lapping up onto the flanks of Cerro
San Luis Obispo (just west of the center of town) are very unlikely in fact to be significant deep recharge
zones. Thus, the most reliable representation of the watershed areas where i nfiltration SCMs will yield
the widest range of benefits is likely restricted to where the mapped extent of the groundwater basin
coincides with the mapped areas of WMZs 1 and 4. This includes much of the southern and central part
of the City proper, plus other areas within the watershed to the west and east of the city along the Los
Osos –Edna valley.
39
4.1.2 Improved Access to High -Priority Steelhead Reaches
Figure 4-2. Watershed-wide map highlighting the stream segments previously observed to be dry or with v ery low
summertime flow. Various fish-passage barriers, mainly partial and/or seasonal, identified by CDFW, are shown
with geometric symbols. Underlying colors highlight the WMZs across the watershed.
40
Figure 4-2 highlights previously identified areas of s ummertime dry stream reaches, which are
concentrated through the center of the City (Figure 4 -3).
Figure 4-3. Key habitat reaches through the central area of the City of SLO.
LEFT: Seasonally transitional and dry reaches, with good steelhead rearin g and spawning habitat.
RIGHT: Same view with all “key reaches” highlighted uniformly (either good-quality steelhead habitat or
dry/transitional reaches blocking access to habitat reaches). Overlay shows the mapped extent of the San
Luis Obispo groundwater basin; note the close correspondence of these critical reaches with the geologic
conditions associated with groundwater infiltration and aquifer storage.
41
4.1.3 Flood Reduction and Water-Quality Improvements
The information needed to generate estimates of where the greatest benefits to flooding and water -quality
impairments is derived from recent work by 2ndNature for the City of San Luis Obispo, which involved
modeling of both runoff and particulate pollutant generation (see 2ndNature , 2016). Their results are
mapped in Figure 4 -4 from their model-based analysis for the city . The spatial patterns of pollutant
generation closely follow the distribution of impervious area across the city, with the central business
district showing the highest values and un developed outlying areas the least.
Figure 4-4. LEFT, stratified runoff-generating subcatchments (red = highest runoff per unit area, yellow =
intermediate, green = lowest); RIGHT, particulate pollutant generation (pink = highest per unit area, green =
intermediate, blue = lowest).
42
4.1.4 Opportunities for Integrated Benefits
Because the overarching goal of this SRP is to explore the potential multiple benefits of stormwater
management strategies across the variety of conditions in a given jurisdiction or w atershed, the results of
the previous evaluations are best viewed in combination. The following maps (Figure 4-5) display the
spatial relationship between areas of high est runoff/pollutant generation, significant opportunities or
impairments to instream ha bitat, and the presence/absence of groundwater resources. This integrated
spatial context , overlaying the quantifiable attributes and focusing on where the highest -rated areas
within each category overlap, provides the framework in this SRP for identifying the highest priority
areas for management actions.
43
Figure 4-5. TOP MAPS: Intersection of major runoff-
generating (top left) and pollutant-generating (top
right) areas, the San Luis Obispo groundwater basin
(cross hatching), and priority steelhead-habitat
reaches (purple and green reaches). Those areas
expressing the greatest level of resource value and/or
impairment are almost entirely underlain by WMZ 1,
suggesting that infiltration of stormwater is likely to
be feasible in these areas and would have wide -
ranging benefits.
BOTTOM VIEW: The same area as above with an
airphoto base, showing that these key areas cover
much of the urban core of the City of San Luis
Obispo. This suggests that SCMs suitable for urban
retrofitting and redevelopment are likely to be the
most feasible and effective. In addition, a largely
undeveloped area west of US Highway 101 in the
southwest corner of these maps presents a promising
opportunity for non-structural measures to preserve
likely beneficial conditions still present in this area.
44
4.2 NON-QUANTIFIABLE CRITERIA
Determining and ra nking sites and projects based on non-quantifiable benefits may be an important
adjunct to the quantifiable benefits (Table 4 -2) in some circumstances , because any effort to quantify
benefits includes critical and inescapable shortcomings: it cannot fully incorporate critical elements of
project feasibility and social justice, it requires quantification of poorly predicted parameters (e.g.,
biological improvement resulting from a projected management action), and it require s a high level of
modeling effort that can be disproportionately large relative to the total available planning and/or
implementation resources.
4.2.1 A Framework for Assessing Non-Quantifiable Benefits
A useful framework for considering these non -quantifiable benefits (and constraints) has been developed
for the Washington State Department of Commerce (2016); its recommended steps for determining an
appropriate prioritization are summarized as follows:
Step 1: Fish Use and Aquatic Habitat (or other important beneficial uses)
Review the receivin g waterbodies or receiving waters in the watershed for actual or
potential fish use with a focus on the biological conditions and potential for environmental
lift. Give higher priority to receiving waterbodies or receiving waters with low to moderate
levels of impairment as assessed using the following data:
Percentage of tree canopy/condition of buffer for habitat and shade (This may also
be considered at Step 2.)
Benthic Index of Biotic Integrity (B -IBI) as an indicator of biological conditions.
Known water quality impairment – 303(d) listings and Total Maximum Daily
Loads (TMDLs), local knowledge, or low instream flows – that impact fish
mortality and use.
Step 2: Flow Control/Low Impact Development (LID) and Runoff Treatment Opportunity Assessment
Review the watersheds for opportunities to address flow control issues or provide runoff
treatment. Give higher priority to watersheds within which stormwater management
improvements are expected to accelerate environmental improvement.
Percentage of impervious area/land cover in the watershed containing the
receiving waterbodies or receiving waters.
Comprehensive plans and zoning - Understanding the potential for growth in the
watershed is necessary for prioritizing and planning stormwater retrofit projects
appropriate for the watershed’s future.
Extent, age and condition of stormwater management treatment and flow
control infrastructure – an assessment of the need for retrofitting.
Ripeness to proceed (local knowledge, aligns with programs such as tree
planting and stormwater capital improvement plan, etc., that will accrue
water quality or stream flow benefits).
Watershed area data (inside vs. outside jurisdictional boundaries) – Give higher
priority to receiving waterbodies or receiving waters in watersheds where the
municipality can exert greater influence.
Presence of culverts or other barriers, including natural barriers, to fish
passage.
45
Step 3: Environmental Justice and Social Equity Considerations
A city or county may determine that there are equity and social or environmental justice
issues that need to be addressed in a watershed. If two or more watersheds are determined
of equal priority using the other data sources listed above, consideration of environmental
justice or social equity criteria should be included to prioritize a watershed for stormwater
retrofit investment.
4.2.2 Source Control of Pollutants as a Non-Quantifiable Benefit
“Source control” is defined as any type of stormwater control measure (SCM) that is intended to prevent
pollutants from entering stormwater (National Research Council 2009), including their introduction into a
storm drain system or waterbody. These measures can include product substitution for retail sales or
commercial applications, grading and erosion control, and conservation of open space. In practice, t his
definition credibly includes any full ret ention of runoff on -site such that the only “discharge” is through
evapotranspiration or infiltration through a medium (i.e., the soil) t hat fully traps any pollutants on -site.
Thus, LID practices such as permeable pavement, green roofs, and the suite of retention/infiltration
practices are all expressions of a source-control strategy. The ability to quantify their benefits, however, is
highly variable, and so this category is included here as one of the “non -quantifiable” criteria. Although
measurable results from source control can be demonstrated (the dramatic reduction of lead in the
environment following its phase-out in gasoline is a classic example), most other examples are far less
clear -cut.
4.2.3 Application of Non-Quantifiable Benefits in the San Luis Obispo Creek Watershed
In this SRP these non -quantifiable benefits are not explicitly included in the ranking of projects for two
reas ons. First and most importantly, there is much overlap between the quantifiable criteria presented in
Section 4.1 and the non -quantifiable criteria discussed here, particularly those of “Step 1” and “Step 2”
from the Washington State Department of Commerce. Most of the structural SCMs emphasized in this
plan also meet the general goals of source control—namely, the retention of pollutants onsite (via
retention of the runoff that carries them ; see Section 4.3, below). This suggests that the distinction
between these two “types” of criteria may in part be artificial . It also risks an outcome whereby less
suitable projects could be ranked more highly on the basis of a quantitative score while overlooking more
broadly beneficial projects.
In the immediate case of the City of San Luis Obispo, however, a second reason renders the discrete
consideration of “non -quantifiable criteria” moot. The City’s relatively modest financial and staff
resources , and limited geographical area , preclude any need to engage a complex mix of scored and non -
scored criteria to identify the highest -ranked sites. Subsequent analyses (Section 5.4, below) identify a
large number of project sites that achieve the highest ranking for every criterion, and so neither site
weightings, identifying priority watersheds, nor “tiebreaker” considerations are needed. Instead, this SRP
applies an integrated method that emphasizes treatment of the areas most important for restoring key
watershed processes, highlighting the types of SCMs that will prove suitable for restoring those
processes. This approach generates a list that will likely exceed the City’s capacity for implementation
over the functional lifetime of this plan, and for which opportunistic implementation (r ather than a
ranking based on progressively less important criteria) is likely to be the most effective strategy to
achieve the greatest benefits.
46
4.3 PRIORITY NEEDS AND IDENTIFICATION OF STORMWATER CONTROL
MEASURES
In the areas of greatest integrated impacts to resources (Figure 4 -5 ), the common thread is a loss of
infiltration from the contributing watershed area. Thus, the stormwater management strategies most
responsive to this condition will be those that are most effective at recovering this watershed process in
developed area. From Table 3-1 above, structural SCMs that best address this need would include:
Bioretention (infiltration design)
Porous pavement (infiltration design)
Soil amendments
Downspout disconnection
Infiltration basins
Dry wells
Several of these can be implemented in more broadly characterized “Green Streets” projects; others are
amenable to both site-scale and regional-scale implementation; and still others (including the
incorporation of non -structural LID site design considerat ions) can be implemented more broadly at
relatively low cost, particularly in residential areas. This emphasis on infiltrative SCMs , however, does
not imply that focused water -quality -improvement measures (such as the drop -inlet filters to capture
first -fl ush pollutants being installed in the downtown area) are not also beneficial in addressing water -
resource concerns —only that the watershed-scale impacts of urbanization are most broadly and
pervasively being expressed through the impairment of infiltration .
Presently unavailable is information on any direct linkages between consumptive water use from the San
Luis Obispo groundwater basin and any declines in the level of a near -surface water table that might
affect streamflow. The only relevant data made ava ilable for this study, for the upper watershed area and
presented in Section 1, are equivocal as to whether any systematic trends in changing water -table
elevations exist. They do suggest, however, that an unsaturated zone of some tens of feet thick lies
b etween the ground surface and the water table, which would render fluctuations in the water -table level
largely or totally irrelevant to changes in stream discharge. This condition, if widespread, would also
limit the direct relevance of groundwater rechar ge to instream flow by (for example) stormwater
infiltration, except for near -stream localities where shallow groundwater (i.e., “interflow”) might reach
the channel directly before the water infiltrates more deeply.
Regardless of direct improvement to pot able water supply, infiltrative SCMs are best suited to improve
the overall health of the groundwater basin. Given the general suitability of the central, urban parts of the
watershed to infiltration, recovering or protecting this watershed process should be the primary focus of
stormwater management in these high -priority areas. Such measures would also contribute to the
recovery of a more natural hydrograph during storm periods and improve water quality, both of which
likely contribute to the substantial monotonic decline in stream health (as measured by the California
Stream Quality Index and reported in Section 1) that currently exists.
In “near -stream ” areas (likely measured in 10s or 100s of feet, but with no direct data to define more
precisely), some improvements to instream flows might also be expected from these measures.
Elsewhere, however, only the replacement of direct offtake of surface water (if any exists) by capture -
and-reuse is likely to directly benefit instream flows.
Outside of the highest priority areas —identified in Figure 4 -5 where lack of instream flows, modeled
stormwater -related problems, and infiltration opportunities coincide —the lens of watershed processes
still offers clear guidance for stormwater management. Particularly in the unincorporated areas of the
47
watershed, the groundwater basin underlies primarily grassland/herbaceous and agricultural land uses.
These areas are presumably functioning well at present for supporting infiltration, but any future urban
development in them should emphasize infiltration as both necessary and likely feasible (the entire area
is underlain by WMZs 1 or 4) (Figure 4-6).
Figure 4-6. The San Luis Obispo Creek watershed where underlain by the mapped groundwater basin (cross -hatched
area), highlig hting the predominately grassland and agricultural land uses outside of the urban core.
48
Significant runoff- and pollutant -generating areas as identified by 2ndNature (2016) are also present
outside of the groundwater basin, particularly along the Broad Street corridor to the southeast of the city
center. This area is mapped as a pa tchwork mosaic of WMZs 1 and 3; recent subsurface exploration
suggests that most of the area is probably underlain by impermeable rock and is more appropriately
managed through out as WMZ 3, with strategies chosen that “promote treatment of runoff through
infiltration and/or filtration, and in general by minimizing overland flow” (CCRWQCB 2013). Virtually
all of the LID project types listed in Table 3-1 can accomplish these tasks , although those that emphasize
deeper infiltration (dry wells, infiltration basins) will likely be less effective in this area than filtration -
oriented bioswales, infiltration trenches, and constructed wetlands/wet ponds.
4.4 MULTI-CRITERIA BENEFITS AND OPPORTUNITIES
The Guidelines seek to encourage multiple benefits from every recommended action. To that end, they
state that “Each project and program implemented in accordance with the Plan should at minimum,
address: (1) at least two or more Main Benefits l isted in Table 4 ( e.g., see Tables 4-1 and 4 -2 of this
document) within the watershed or sub -watershed, and (2) as many as feasible Additional Benefits for
the same project/program.” The referenced categories of “main benefits” that are most likely to app ly to
prospective stormwater management SCMs in the San Luis Obispo Creek watershed are as follows:
Increased filtration and/or treatment of runoff
Decreased flood risk by reducing runoff rate and/or volume
Environmental and habitat protection and improvem ent
Increased urban green space
Public education
Other main benefits listed by the Guidelines but less likely to apply are water supply reliability,
conjunctive use, and employment opportunities.
A number of “additional benefits” from the Guidelines are also likely to be achieved from prospective
actions in the watershed, and their consideration will be incorporated into the final identification and
ranking of projects and programs (see next section of this report):
Nonpoint source pollution control
Reestablished natural water drainage and treatment
Reestablishment of the natural hydrograph
Water temperature improvements
Enhance and/or create recreational and public use areas
These multi-criteria benefits are implicit in the approach used to identify high -priority projects, because
the highest ranked projects are only those where multiple benefits are already id entified. This outcome
highlights an additional benefit of using a watershed -process approach: rather than targeting specific
symptoms (e.g., high pollutant concentration) this SRP target s underlying causes. In so doing, the desire to
address the varied manifestations of those impaired processes, which are collectively term ed “benefits,”
is fully incorpor ated.
49
5 SCREENING AND RANKING PROJECT OPPORTUNITIES IN THE
WATERSHED
5.1 PROJECT CATEGORIES
Developing a set of potential projects and non -structural actions for the San Luis Obispo Creek watershed
benefit s from other recent efforts, notably the recently released draft Stormwater Resource Plan (SRP) for
San Mateo County and the Watershed Management Plans (WMP s) for the Lower Los Angeles and San
Gabriel Rivers. These precursors are not directly applicable to San Luis Obispo in all aspects —they cover
larger areas, and the financial and organizational resources available both to develop th os e plan s and to
implement their recommended projects are dramatically larger —but they nonetheless offer useful
guidance.
Fr om these prior efforts, four broad categories of structural projects can be usefully identified:
1. Regional capital improvement projects (CIPs)
2. Parcel-scale Low Impact Development (LID) retrofits
3. Parcel-scale LID for new (public -agency) construction
4. Green st reets
Within these categories, prior reports have each identified a set of ranking criteria. Both the San Mateo
SRP and the LA/San Gabriel River WMPs only included publically owned parcels and public road right -
of-ways for consideration for structural proj ects. Although a reasonable approach for both financial and
feasibility reasons, the distribution of public property relative to the ability to address water -resource
problems within the watershed is unlikely to be optimal. For purposes of identifying pote ntial structural
projects this approach is maintained here, but identifying and ranking prospective sites obviously could
apply to public and private property alike.
5.1.1 Regional Capital Improvement Projects (CIPs)
The San Mateo SRP specified the following cri teria for identifying and ranking prospective sites that
could be suitable for large-scale capital improvement stormwater -management projects :
Land use (undeveloped best, built out worst)
Impervious area in contributing area (higher is better , because the opportunities for
improvement are greater ); absent direct determination of contributing area, the San Mateo
SRP assumed a representative drainage area = 500x parcel area, max 1000 acres , with the site at
center of the area
Parcel size (larger is better, mi nimum >0.25 acres)
Hydrologic soil type (A best, D worst)
Slope (flatter is better, and in all cases <10%)
The Los Angeles River WMP took a more specific look at the variety of land uses that might be suitable
for CIPs , ranking them as follows (most to least suitable):
Open space and recreation
Educational uses
Government institutions
50
Golf courses
Commercial
5.1.2 Parcel-Scale Low Impact Development (LID) Retrofits
The San Mateo SRP specified the following criteria for identifying and ranking prospe ctive sites that
could be suitable for p arcel-scale low impact development (LID) retrofit projects (LID for new private
construction is already required through the Central Coast Regional Water Quality Control Board’s post -
construction stormwater management requirements under the NPDES MS4 permit ):
Parcel land use (more intense is better, to maximize the potential for pollutant removal)
Impervious area on parcel (higher is better, also for maximization of effect)
Hydrologic soil type (A best, D worst)
Slope (flatter is better, and in all cases <10%)
5.1.3 Parcel-Scale LID for New (Public-Agency) Construction
This category was not explicitly included in either th e Los Angeles/San Gabriel River WMPs or the San
Mateo SRP, highlighting a potential lack of integration between stormwater management and other
elements of th ose jurisdictions’ capital planning and implementation process. Such opportunities,
however, are r ecognized in the San Luis Obispo Creek watershed and are discussed on a site -by-site basis
in Section 5.4 of this plan.
5.1.4 Green Streets
The San Mateo County SRP specified the following criteria for identifying and ranking prospective road
segments for green street retrofitting:
Type (neighborhood arterials, local streets, alleys, parking lot access)
Impervious area in contributing area (higher is better) (absent direct determination of
contributing area, assumed a representative drainage area = 85 ft each side of road
centerline)
Hydrologic soil type (A best, D worst)
Slope (flatter is better, and in all cases with a roadway slope <5%)
The San Mateo County SRP also identified “other criteria” for consideration, echoing the Guideline’s
requirement for a range of community and multiple benefits. For the San Mateo County SRP, these
included:
Flood-prone streams
PCB risk areas
Co-located planned projects
Drains to TMDL waters
Multiple benefits
o GW recharge
o Source control
o Hydrologic process restoration
o Habitat and open space enhancement
o Community enhancement
51
5.2 GENERAL APPROACH FOR PROJECT SCREENING AND RANKING
Compiling the prior approaches described above, and integrating them with the additional focus on
instream habitat protection and enha ncement in San Luis Obispo Creek, suggests the following set of
criteria for the screening and ranking of project sites in the San Luis Obispo Creek watershed that will be
followed in the subsequent sections of this SRP :
1. Parcel ownership
2. Parcel land use/road type
3. Parcel impervious coverage
4. Parcel/road slope
5. Parcel size
6. Contributing drainage-area pollutant loading
7. Contributing drainage-area runoff generation
8. Proximity to critical habitat reach
9. Infiltration feasibility
10. Groundwater basin recharge potential
11. Existing planned projects
12. Existing known drainage/flooding problems
13. Opportunities for direct capture/reuse
14. Public visibility/education
Not every one of these criteria is applicable to each of the four categories of structural projects (Section
5.1), and they are not all of equivalent importance. Some speak to the ultimate feasibility of a project (e.g.,
infiltration basins are not feasible where the soil does not drain, or where the slope is steep); others
provide a more nuanced discrimination of where (or whether) a particular project type at a particular
location is likely to have high benefits. Thus, they are listed in the next section by project category, and
further discriminated into those that address feasibility (i.e., “go/no -go”) and those that can guide project
ranking and prioritization.
In addition, not all of these criteria can be equally well -defined on every parcel in the city or watershed .
In particular, the last two criteria on the list presented above are not well-suited to a synoptic, GIS-based
analysis of prospective regional CIP sites , namely public visibility/education and opportunities for direct
capture/reuse. Although both are important potential benefits of a project, they are unlikely to be useful
discriminators at an early planning stage. Direct capture/reuse should be feasible on any project that
includes hard surfaces (for capturing runoff) and landscaped areas (for making use of that runoff so
captured). As an added benefit its value is clear; however, as a site discriminator it does not appear to
bring much additional power in a majority of likely situations. Public visibility is, potentially, a function
of proximity to high -traffic areas and can probably be crudely discriminated on a case -by-case basis .
For t h ose criteria that are amenable to characterization and/or quantification on a watershed scale, the
methods for their determination are as follows:
Parcel ownership within the San Luis Obispo Creek watershed was taken from the “owner” field
in the San Luis Obispo County parcel database, with the city, county, and school districts all
presumed to be under public ownership .
52
Parcel land use was determined by the National Land Cover Database, wherein all categories
except low -intensity, medium -intensity, and high -intensity urban development (NLCD categories
22, 23, and 24) were assumed to have sufficient building -free space suitable to their overall size.
Road type was obtained from the TIGER classification of road segments, available for all roads
throughout th e watershed.
Parcel impervious cover was not directly calculated, although it is the dominant factor in
determining runoff and pollution generation (below) and so is indirectly included in all
evaluations.
Slope of a parcel or road segment was determined directly from GIS from the included (or
adjacent) land area.
Parcel siz e (i.e., area) was taken directly from GIS.
Runoff and pollutant generation was quantified from recent modeling effort done on behalf of
the City of San Luis Obispo by 2ndNature (2016). For purposes of screening and ranking in this
SRP, the areas of “high” runoff and pollutant generation within the city limits were defined as
areas modeled by 2ndNature to be in their upper -most category of unit -area runoff or pollutant
generation.
Habit at reaches, identified as “key” by virtue of their existing quality or their potential barrier to
upstream areas due to low summertime flow, are presumed to benefit from the reinfiltration of
stormwater in relatively close proximity. Absent a detailed hydr ogeologic study there is no way
to assign a defensible threshold value for what constitutes “close”; for purposes of
acknowledging the importance of this criterion and incorporating it into the ranking, a distance
of no more than 1000’ between a prospectiv e CIP-hosting parcel and a key reach was assumed to
provide benefit. Note, however, that proximity to steep or unstable stream banks should preclude
infiltration regardless of its potential benefits, a geotechnical determination that should be made
on a site-by-site basis wherever this potential risk arises.
Infiltration feasibility made use of the Central Coast Regional Water Quality Control Board’s
designation of Watershed Management Zones (WMZs), wherein WMZs 1 and 4 identify areas
with suitable geology for infiltration and slopes <10%.
Areas of value for groundwater basin recharge are well -defined by the mapped extent of the San
Luis Obispo groundwater basin, which extends under much of the city.
Existing planned public capital projects (i.e., non -stormwater) and redevelopment plans are
identified through the City’s capital process; those in an early stage of implementation and with a
potential to incorporate a significant additional element of stormwater management have been
included in this ranking p rocess.
Existing flooding problems are widely recognized by City staff and reflected in upcoming project
work; these areas include the downstream -most reach of San Luis Obispo Creek as it leaves the
city. Thus, the entire city area is contributory to this problem (since it lies at the downstream -
most boundary of the city), and so this criterion (although important) does not provide any
useful spatial discrimination or prioritization of prospective project sites.
53
At this stage of project/site ranking, differential “weights” were not assigned to the various criteria. Those
attributes that determine feasibility are assumed to be “all or nothing”—either a site meets all of the
feasibility criteria, or the prospective project type is simply not feasible. For t hose that are judged feasible,
the highest -ranked sites will invariably be those that achieve the highest ranking for every criterion,
regardless of a weighting scheme. Because the likelihood is low that a city such as San Luis Obispo could
implement every top-rated project during the meaningful design lifetime of a plan such as this one (and
so need to discriminate amongst lower -ranked projects), a more detailed scoring/weighting/ranking
system is not applied at this time. However, through the process of p lan implementation such a
refinement could be added in the unlikely event that it was ever judged to be necessary.
5.3 CRITERIA FOR PROJECT SCREENING AND RANKING
5.3.1 Criteria for Regional Capital Improvement Projects (CIPs)
These projects are assumed to collect runoff from a drainage basin or subbasin that extends beyond the
property boundaries. As typically implemented by an individual jurisdiction, they are identified on the
basis of existing stormwater-related problems that have no clear regulatory or programm atic resolution,
and that therefore require the expenditure of public funds to address a known issue. Thus, the
identification or their need and priority is based on existing conditions, under that assumption that
regulations on new development will be sufficient to avoid future problems (but not to rectify existing
ones). Given the multi -benefit focus of SRPs and issues of both instream flow and groundwater supplies,
the fundamental attribute of all potential CIPs in this plan is their ability to infiltrate stormwater to
restore the key watershed processes of infiltration and interflow that have been impacted by urban
development.
Feasibility
1. Parcel ownership (i.e., public)
2. Parcel size (based on the San Mateo SRP, a threshold of 0.25 acres was identified to allow space
for a regional facility)
3. Parcel land use (undeveloped or only lightly developed, e.g. parkland; existing buildings or other
structures were assumed to render a site infeasible for a stormwater facilit y)
4. Infiltration feasibility
5. Parcel slope (<10%)
Ranking criteria (listed by relative importance)
6. Existing known drainage/flooding problems
7. Contributing drainage area runoff/pollutant generation
8. Groundwater basin recharge potential
9. Existing planned projects
10. Public visibility/education
11. Proximity to key habitat reach
12. Opportunities for direct capture/reuse
54
5.3.2 Criteria for Parcel-Scale Low Impact Development (LID) Retrofits
Feasibility
1. Parcel ownership (i.e., public)
2. Parcel size (to discriminate from regional facilities, a maximum size threshold of 0.25 acres was
used)
Ranking criteria (listed by relative importance)
3. Infiltration feasibility
4. Parcel slope (<10%)
5. Public visibility/education
6. Opportunities for direct capture/reuse
7. Parcel impervious area
8. Groundwater basin recharge potential
9. Existing known drainage/flooding problems
10. Proximity to key habitat reach
Almost by definition, virtually any parcel can benefit from some degree of stormwater retrofitting. Thus,
“feasibility” is somewhat arbitrary and is here limited to public parcels that are too small for
consideration of regional facilities. Nonetheless, other jurisdictions have had good success with incentive
programs for installing LID on private properties, and even a large parcel can host parcel -sca le LID
features. These alternatives are not considered further in this SRP, but they are available strategies for
future consideration.
Many of the criteria for regional CIPs also are relevant to parcel -scale retrofits with some minor
modifications. For ex ample, some, but not all, retrofit SCMs are infiltrative and are slope-dependent;
others, such as rain barrels or cisterns , are not. Impervious cover may constrain the types of LID that can
be included on a site, but even high impervious coverage is unlike ly to preclude their implementation
altogether. Thus, these are “ranking criteria” but not fundamental determinants of feasibility.
Parcel-based retrofits are the most direct form of public outreach to residents and businesses in the realm
of stormwater ma nagement, and they are the easiest to redirect high -quality runoff (i.e., roof runoff) back
into secondary uses. However, they are unlikely to be sufficiently widespread to affect “regional”
stormwater issues (i.e., groundwater basin recharge, regional flo oding, or instream dewatering) without
an extensive, long-term program to drive widespread implementation . For these reasons, the overall set
of criteria for identifying prospective LID retrofit sites is nearly equivalent to those for regional CIPs , but
their order of importance differs in part.
5.3.3 Criteria for Parcel-Scale LID for New (Public-Agency) Construction
Feasibility
1. Parcel ownership (i.e., public)
2. Existing planned projects
3. Parcel land use type
55
Ranking criteria (listed by relative importance)
4. Infiltration feasibility
5. Parcel slope (<10%)
6. Public visibility/education
7. Opportunities for direct capture/reuse
8. Parcel impervious area
9. Groundwater basin recharge potential
10. Existing known drainage/flooding problems
11. Proximity to key habitat reach
This project category has similar considerations as for parcel -scale retrofits, but there are greater
opportunities for more extensive, and less costly, alternatives for not -yet -built projects than when
retrofitting SCMs into existing land uses. Potential sites were identified from the city -wide capital
projects list and conversations with City of San Luis Obispo Public Works officials, and a discussion with
facilities planners at CalPoly.
5.3.4 Criteria for Green Streets
Feasibility
1. Road type (neighborhood arterials and less intensely used roadways)
2. Road slope (<10% hillslope gradient)
Ranking criteria (listed by relative weighting)
3. Existing planned projects
4. Public visibility/education/aesthetics
5. Contributing drainage area runoff/pollutant generation
6. Infiltration feasibility
7. Proximity to critical habitat reach
8. Existing known drainage/flooding problems
This project category also shares many of the same considerations as for the others, except that the unit of
consideration is a road segment rather than a parcel. Categories of roads included are the US Census’s
TIGER classifications for generally moderate to low -intensity road use types S1200, S1400, S1730, and
S1780 (secondary road; local neighborhood road, rural road, city street; alley; and parking lot road,
respectively). The San Mateo County SRP made use of a road-segment slope threshold of <5%; to avoid
calculating this for each segment at the stage of initial screening, this criteria was substituted with a
hillslope gradient of the surrounding terrain of no more than 10%.
In general, green streets are most easily implemented during initial construction and provide great
opportunities for public visibility. They are most useful for water quality improvement via infiltration or
filtration, but (unlike other LID application s) reinfiltration to deep groundwater is not a high priority
given the potential water -quality concerns associated with road runoff.
56
5.4 RESULTS OF SCREENING AND RANKING
5.4.1 Results for Regional Capital Improvement Projects (CIPs)
The San Luis Obispo County dat abase lists about 250 separate parcels under public ownership in the
watershed (although a number of these “separate” parcels share the same assessor's parcel number). Of
these, 102 meet the basic feasibility criteria for regional CIPs (i.e., size >0.25 acres, land use other than
low -, medium -, or high-intensity urban, WMZ = 1 or 4). Figure 5 -1 highlights their locations, emphasizing
how few are particularly well -located to provide meaningful treatment of urban runoff before its entry
into the channel network. Table A-1 (see Appendix) lists them by identifying number and Assessor Parcel
Number, together with their attributes for purposes of ranking. The most significant limitation is the
interplay of land cover and key habitat reaches —parcels in proximity to the stream channel where it is
most impaired are, typically, already developed and so are judged infeasible as sites for regional projects.
Of the nominally feasible parcels for regional CIPs listed in Table A-1, only 12 are high in all of the
ran king criteria (recharge, runoff and/or pollutant loading, proximity to key reaches) (Table 5 -1). Many of
the other prospective sites listed on Table A-1 (and displayed on Figure 5-1) are in areas of less intense
land use but, as a consequence, are not high pollutant generators. What remains are the project sites that
would be most highly ranked regardless of the quantitative scoring or weighting method used.
Table 5-1. All pubic parcels >0.25 acres that are highly ranked in all scoring criteria (mapped on Figure 5-2).
Unique
Identifier #
Assessor’s
Parcel Number
Parcel size
(acres)
Overlies
GW basin?
Runoff
class
Pollutant
load class
Near critical
habitat?
1 001-205-014 0.92 yes >0.80 yes
4 003-511-022 0.85 yes >0.80 >0.10 yes
8 002-321-004 1.11 yes >0.80 >0.10 yes
12 002-421-031 0.56 yes >0.80 >0.10 yes
16 003-515-001 3.21 yes >0.80 >0.10 yes
44 053-051-045 48.06 yes >0.80 yes
47 053-131-013 13.95 yes >0.80 yes
49 053-141-012 21.92 yes >0.80 yes
51 053-272-027 1.76 yes >0.80 >0.10 yes
66 001-181-006 0.90 yes >0.80 yes
100 002-423-006 1.35 yes >0.80 >0.10 yes
115 053-152-007 3.25 yes >0.80 yes
57
Figure 5-1. Preliminary screening of public parcels with potential suitability to host a regional stormwater CIP. All
public parcels that meet the feasibility criteria for non-intensive urban land use and flat infiltrative ground (WMZ = 1
or 4) are shown in yellow; all other public parcels not meeting one or more of these criteria are shown in pink.
58
Figure 5-2. Highlighted by red cross-hatching are those parcels displayed on Figure 5-1 meeting the feasibility criteria
that are also >0.25 acres and rate highly in each of the ranking criteria (recharge, runoff and/or pollutant loading,
proximity to key reaches). Only 12 such parcels meet all of these requirements (listed on Table 5-1).
59
5.4.2 Results for Parcel-Scale Low Impact Development (LID) Retrofits
In contrast to the regional CIP sites, only 23 small (<0.25 acres) publicly owned parcels that meet the
feasibility criteria are present in the watershed. Of these, only seven meet even two of the ranking criteria
(turquoise-shaded on Table 5-2 , orange-highlighted on Figure 5 -3 ), suggesting that although modest
benefits may accrue from implementing LID retrofits on small public parcels, this approach is unlikely to
achieve major system -wide benefits.
Table 5-2. The full list of small publically owned parcels in the watershed that meet feasibility criteria for parcel -scale
LID. Turquoise -highlighted parcels rate highly in at least two ranked criteria; only one ranks highly in all four such
criteria. Parcels are mapped on Figure 5-3.
UID APN Parcel size
(acres)
Overlies
GW basin?
Runoff
class
Pollutant
load class
Near crit ical
hab itat ?
2 002-412-003 0.11 yes yes
7 001-235-015 0.22 yes >.80 yes
14 002-401-020 0.09 yes yes
17 003-571-019 0.05 >.80
26 004-741-004 0.20 yes yes
33 004-822-010 0.07
43 053-071-025 0.24
64 001-023-033 0.13 yes yes
65 052-351-043 0.09
76 004-272-049 0.10 yes
88 053-151-038 0.14 yes >.80
91 053-111-062 0.20 yes
102 001-016-003 0.05
103 002-482-012 0.17 yes >.80 >.10 yes
104 004-966-001 0.01
105 004-966-003 0.02
106 004-966-006 0.02
107 004-966-035 0.02
108 004-966-037 0.02
109 004-966-038 0.02
110 004-967-037 0.02
111 004-967-038 0.02
117 053-022-012 0.14
60
Figure 5-3. That part of the watershed with public parcels (yellow) that are too small to host a regional CIP (i.e., that
are <0.25 acres) but meet at least two of the criteria for high ranking (highlighted in orange ; see Table 5-2).
61
5.4.3 Results for Parcel-Scale LID for New (Public-Agency) Construction
Only a modest number of planned pubic -agency projects are at a stage where good advantage can be
taken to incorporate a level of LID that might otherwise not be required by existing Regional Board
requirements for post -construction stormwater management. W ithin the City of San Luis Obispo,
potential projects were identified in consultation with City staff from the Public Works Department . With
their guidance a subset of those on the City’s master CIP list were identified on the basis of their potential
for incorporation of stormwater management features and a sufficiently early stage of implementation to
improve that likelihood that such integration could actually occur. In addition, the South Broad Street
Area Plan was recognized as a promising area for pot ential incorporation of LID into an area slated for
redevelopment; although it is not presumed to be wholly (or even primarily) constructed by public
agencies, its inclusion in this planning document appears appropriate given its early stage of
implementat ion.
Overlapping of these public projects with the identified opportunities for regional or local -scale
stormwater retrofit projects (Table 5-3 and Figure 5 -4) suggests a number of prospects for integration
with anticipated new construction.
Table 5-3. Pr ojects on the City’s current CIP list that meet appear promising for the incorporation of LID features into
their final design, and that are at no more than 20% completion as of early 2017 to reduce the difficulties of late -stage
design changes (with the e xception of #105, which already includes a substantial drainage -related component).
Turquoise -highlighted projects are particularly well-positioned to align with highly ranked sites listed on Tables 5 -1
and 5-2 (regional and parcel-scale retrofits), although virtually all appear to fall within areas well-suited for
incorporating LID into their final design. Projects are mapped on Figure 5-4.
City
CIP # Project Status
% Complete
(as of early
2017)
20 Bldg - Mission Plaza
Restroom - 2019 Estimated Construction Date: 1st Quarter 2019 0
21
Bldg - Police Facility Site
Assessment: 1016 or 1042
Walnut Street, SLO
Study Status: On-call architectural services contracts to
be awarded by end of September 2016.
Budget Status: On Budget. 100% budget remains
Estimated Study Start Date: Phase 1 - Site assessment
study to begin 3rd Quarter 2016. Police department
needs for new facility tabulated.
10
27
Bridge - Prado at
Higuera Replacement
2018
Design Status: Phase 1 (Feasibility Analysis) complete.
Phase 2 (PSR/PR & Environmental) 50% complete. Phase
3 (PS&E) to begin 4th quarter 2016.
Budget Status: On budget for Phase 1 (Feasibility
Analysis) and Phase 2 (PSR/PR).
Estimated Construction Dat e: 2018-19
5
102 Bridge - Santa Fe at Tank
Farm 2018
RFP for design and preliminary investigation services
being prepared for circulation with on-call design firms.
62
City
CIP # Project Status
% Complete
(as of early
2017)
8
Misc - 2016 FS 2 Ext
Driveway Slab
Replacement: 126 or 136
North Chorro Street
Design Status: Information gathering complete. Project
layout complete. Ready to commence slab subgrade
testing after 50% meeting.
Budget Status: On Budget. No design budget spent.
Estimated Construction Date: Start date 3rd Quarter 2017
(July).
20
45
Park - Meadow Park
Pedestrian Bridges
Replacement1
Design Status: 50% Plans & Specs due at the end of the
first quarter 2017.
Budget Status: On budget, 10% of design budget
expended.
Estimated Completion Date: Plans and special
provisions by end of 3rd quarter 2017.
55 Pkg - Palm -Nipomo
Parking Structure
Council authorized moving forward with Environmental
review on 1-19-2016
Project will move into next stage of
design/environmental but will wait for new Parking
Manager to assume project management oversight.
Internal meetings being coordinated in the mean time.
0
1 Sts - California Taft
Roundabout
Design: 0%. RFP for design services sent to On-Call
consultants. Due back August 26, 2016
Budge Sta tus : On budget. 0% used.Estimated
Construction Date: N/A. Funding has only been
allocated for design at this point.
0
105
Sts - Higuera at 50
Higuera Widening: 50
Higuera, from Madonna
to the end of Caltrans
Design completed, permitting and right -of-way
acquisition in process 50
4
SW - 2018 Silt Removal--
8 locations, locations to
be provided
Design Status: Finalized project scope and held scope
meeting. Preparing request for proposals for
environmental consultant.
Budget Status: 100% budget remains
Estimated Construction Starts date: Q3 2018
5
63
City
CIP # Project Status
% Complete
(as of early
2017)
5
SW - Buchon and Santa
Rosa Storm Drainage
Improvements Project
Design Status: 50% PS&E Prepared. Due to cost, other
alternatives are now being evaluated.
Budget Status: On Budget, No Design budget has
currently been spent.
Estimated Construction Date: 3rd quarter 2017
10
1An additional capital project at this location, Meadow Park Stormwater Capture and Use Project (City project # 2017
SC-02), was identified too late for inclusion in the current City -wide CIP list (i.e., this table) but has been proposed
for consideration through the San Luis Obispo County Region Integrated Regional Water Management Program. It
would divert and capture existing high stormwater runoff flows from the Broad Street neighborhood that currently
enter Meadow and San Luis Obispo Creeks, storing it f or later use for park irrigation.
64
Figure 5-4. Map of public CIP projects in the City of San Luis Obispo in an early stage of planning/implementation,
and thus where incorporation of LID features may be both beneficial and feasible. The South Broad Street Planning
Area is outlined in yellow near the center of the map; other projects are labeled with red squares. Nearly all lie on
WMZ #1 (purple background), sugg esting a high feasibility for infiltration -type SCMs ; only a portion of the South
Broad Street area and part of the California -Taft roundabout likely occupies sites with sub -optimal infiltration
characteristics. Identified high -priority regional parcels and parcel-scale sites (from Figures 5-2 and 5-3) are cross-
hatched.
65
CalPoly also has a formal ma s ter planning process for capital projects that may provide opportunities for
more extensive incorporation of LID-based stormwater management approaches than wo uld be required
under the campus’s current NPDES permit. The final administrative draft of the Master Plan has yet to be
released, and so the details of specific projects and locations are not yet available . However, preliminary
discussions suggest that th e following projects (and their associated elements for green infrastructure or
environmental outreach) are likely to be considered or included in preliminary and final designs:
Slack St and Grand Avenue Residential Neighborhood (420 units)
• Riparia n Enhancement
• Bioswales
• Rain Garden
• Education
Brizzolara Creek Enhancement
• Seasonal Creek (re-establish the natural hydrograph) and Wetland Enhancement (wetland creation)
• Bank Repair (habitat protection and improvement)
• Recreation – Pedestrian/Bike Path
• Outdoor Teaching and Learning Amphitheater
• Bioswales
• Education/Signage
Fermentation Sciences Building
• Bioswales
• Rain Garden
• Rainwater Harvesting (pilot p roject)
• Education
5.4.4 Results for Green Streets
As is evident from the distribution of roads and high -runoff-generating areas of the City (Figure 5 -5)
there is a close association between these two features , providing many opportunities to take advantage
of their physical proximity (and, undoubtedly, causal relationship) to one another in managing
stormwater to achieve broader benefits .
66
Figure 5-5. Roads of in the downtown area of the City , stratified by their TIGER designation (most are category
S1400, “Local Neighborhood Road, Rural Road, City Street”) superimposed on the runoff -generating potential of the
subcatchments throughout the city (red = highest, green = lowest). Note the near -perfect correspondence of dense
roads in and around the c ity center with the areas of highest runoff (and pollutant) generation. This area is also
almost entirely in WMZ #1, meaning that gradients are low and infiltration should be largely feasible.
67
Over the watershed as a whole, over 89 miles of suitable -duty r oads (TIGER classes S1200, S1400, S1730,
and S1780) on slopes <10% are present. Those segments that meet all of the highest ranking GIS -based
criteria (i.e., highest category of runoff and pollutant generation, WMZ = 1 or 4, and proximity to key
reaches) are listed by street name in Table A-2 (see Appendix). In aggregate they total about 13 miles of
roadway, suggesting that this approach to multi -benefit stormwater management is likely to be the most
effective, with the broadest opportunities for implementa tion, in the San Luis Obispo Creek watershed.
Although individual roadway segments on this high -priority list could be further ordered by numerical
criteria, opportunistic implementation of LID features in conjunction with other capital project or
roadway maintenance activities is likely to provide the most feasible path for their construction.
5.5 SUMMARY OF RESULTS
Using the guidance provided by the characterization of the watershed (Section 1), the lens of impaired
watershed processes (Section 3), and the i dentification of sites with the highest rating for addressing
those impaired processes through stormwater management (this section ), key locations within the
watershed and a list of potential projects sites within those areas have been identified (Table 5 -4 ). In
combination with the list s of upcoming scheduled CIPs (Table 5-3 ) and prospective green street retrofits
(Table A-2 ), the City has multiple opportunities for opportunistic implementation of multi-benefit
watershed improvement in the years to come.
Table 5-4. Compilation of identified high-ranked large CIP sites (brown shading) and small LID retrofit
opportunities (green shading) on public parcels throughout the City of San Luis Obispo (from Tables 5-1 and
5-2).
Unique
Identifier #
Assessor’s
Parcel Number
Parcel size
(acres)
Overlies
GW basin?
Runoff
class
Pollutant
load class
Near critical
habitat?
1 001-205-014 0.92 yes >0.80
yes
2 002-412-003 0.11 yes
yes
4 003-511-022 0.85 yes >0.80 >0.10 yes
7 001-235-015 0.22 yes >.80
yes
8 002-321-004 1.11 yes >0.80 >0.10 yes
12 002-421-031 0.56 yes >0.80 >0.10 yes
14 002-401-020 0.09 yes
yes
16 003-515-001 3.21 yes >0.80 >0.10 yes
26 004-741-004 0.20 yes
yes
44 053-051-045 48.06 yes >0.80
yes
47 053-131-013 13.95 yes >0.80
yes
49 053-141-012 21.92 yes >0.80
yes
68
Unique
Identifier #
Assessor’s
Parcel Number
Parcel size
(acres)
Overlies
GW basin?
Runoff
class
Pollutant
load class
Near critical
habitat?
51 053-272-027 1.76 yes >0.80 >0.10 yes
64 001-023-033 0.13 yes
yes
66 001-181-006 0.90 yes >0.80
yes
88 053-151-038 0.14 yes >.80
100 002-423-006 1.35 yes >0.80 >0.10 yes
103 002-482-012 0.17 yes >.80 >.10 yes
115 053-152-007 3.25 yes >0.80
yes
Although the focus of this plan has been on the identification of specific parcels with the optimal
combination of ownership, size, and watershed setting to maximize watershed benefits through
stormwater management, this analysis also should inform the development of non -structural measures to
support attainment of the same goals. Because the Central Coast region already follows the same
framework as presented in this SRP for regulating post -construction s tormwater runoff (CCRWQCB
2013), this key non -structural strategy requires no further emphasis in this plan. Existing water -quality
data do not suggest the presence of any critical contaminants for which product substitution is indicated .
Other non -structural SCMs , particularly those relating to site design and impervious cover limitations,
can be informed by the distribution of areas where infiltration is likely most feasible (i.e., WMZs 1 and 4)
and the infiltrated water providing the greatest range of be nefits.
Although not directly tied to the protection and restoration of watershed processes, other types of SCMs
can also provide multiple benefits with respect to the range of water resources. As noted in Section 5.3.2,
rain barrels or cisterns have broa d applicability an d suitability at a parcel scale because they are not
dependent on favorable soil types and can be incorporated into new construction or re trofitted easily. As
long as locations in need of irrigation are located nearby (and, generally, dow nhill), they represent a low -
cost approach both to reducing the potential downstream impacts of stormwater runoff and to lowering
the demand on potable water supplies. Current research and model results suggest that these capture -
and-reuse SCMs may be essential components of any successful restoration of urban watershed
hydrology (e.g., Burns et al. 2012), but they require widespread implementation to show regional
effectiveness.
Large-scale implementation of stormwater capture is more site -dependent, and identifying specific
localities that meet feasibility requirements is not fully amendable to the regional approach taken in the
SRP. However, prior analyses have already identified one such opportunity in Meadow Park. The goal of
the Meadow Park Capture and Use project (City project #2017 SC-02) is to divert existing high
stormwater runoff flows from the Broad Street neighborhood that currently enter Meadow and San Luis
Obispo Creeks into an underground reservoir, subsequently using th e captured stormwater for park
irrigation . The project has the dual benefits of reducing urban stormwater runoff into the creek network
while decreasing use of the City’s water supply , and it is presently moving towards grant application
through the Integr ated Regional Water Management Plan (IRWMP) process (see Section 6).
69
6 PLAN IMPLEMENTATION
6.1 IMPLEMENTATION PLANS, PROGRAMS, AND PROJECTS
6.1.1 City Processes
In general, proposals for Capital Improvement Project s (CIPs) within the City pass through a well -
established process , which begins with a community -led goal-setting process prior to detailed budget ing.
Requests from the community combined with those of various City agencies lead to staff development of
specific proj ects related to those requests. Prospective CIPs are review ed within an established internal
process, and the Budget Review Team (BRT) then determines how much can be afforded and assigns
priorities to the CIP list. Once the CIP list is approved and prioritized by the BRT, it returns to the staff for
implementation.
For the stormwater-related projects in this SRP, a somewhat wider variety of processes are available for
implementation . CIPs on the 2017 list for implementation have already been screened to i dentify potential
incorporation of LID features for little or no substantive cost change. Standalone stormwater projects will
continue to be identified, designed, and run through the CIP /BRT process for consideration. However,
many of these requests will likely be supported by grant funding, rendering their prioritization through
this process on financial grounds moot .
The update of the 2002 Watershed Enhancement Plan for San Luis Obispo Creek (Land Conservancy of
San Luis Obispo County , 2002), currently in progress by the City, provides a further opportunity to
integrate the multiple benefit approach. Instead of solely focusing on fish habitat, barriers , and
enhancement (as in the original 2002 version), th e updated plan will take a holistic approach to watershed
characterization , consolidating all of the existing creek-related projects and programs under one
organizational umbrella within the City . Stormwater run off, pollution, flood control, transients and
public s afety will be the major new elements of this approach, since every one of these concerns have a
significant impact on watershed health.
6.1.2 IRWMP
The San Luis Obispo County Integrated Regional Water Management Plan (IRWMP), led by the San Luis
Obispo County Flood Control and Water Resources Division , is active in this region (home page at
https://www.slocountywater.org/site/Frequent Downloads/Integrated Regional Water Management
Plan/index.htm ). San Luis Obispo County is taking the lead on their portion of the SRP for their
unincorporated areas, and the City (in conjunction with CalPoly) has responsibility for completing this
SRP for the San Luis Obispo Creek watershed. When completed, the San Luis Obispo Creek watershed
SRP will be integrated into the IRWMP planning process. The IRWMP is expected to be a venue for
implementing many of the projects identified in th is SRP, given its position as a regional entity for
planning and funding.
6.1.3 Decision Support Tools
Two efforts are underway to improve decision -making processes and outcomes . The Program
Effectiveness, Assessment and Improvement Plan (PEAIP) is a n ongoing, comprehensive assessment of
the stormwater management program : how it has been implemented, what ha s been learned, what ha s
been changed, and what ha s been updated. This is intended to allow the City to focus on successes and
dedicate more time and resourc es to what has not worked, or to secure more resources to support a
higher level of service in these areas.
70
In conjunction with the PEAIP, the Regional Water Quality Control Board has required all Central Coast
MS4s to complete the “Spatially -based Stormw ater Volume and Pollutant Loading” mapping exercise
(locally referenced as “The 13267 Letter ”). Under this approach, t he City is broken up into 100 -200 acre
catchment areas. In each catchment area, particulate loading volumes and runoff volumes are calcula ted
based on land-use, geology, hydrology, topography, etc. This is a useful planning tool to see where new
developments might be proposed to go and see what changes to the loading and run off would be. This is
also allows a view into where re-development m ight undo some of the impervious surfaces across the
City’s landscape. This SRP is making use of that analysis (2ndNature, 2016; see Figure 4 -4 above) to
identify the highest priority areas for achieving such improvement s through CIP implementation.
6.2 COMMUNITY PARTICIPATION
Implementation of the recommendations contained in the SRP will engage the community at various
stages. This SRP will be approved by the City Council in an open meeting, and so the community will
have an opportunity to comment on t he plan during a review period prior to the Council meeting. The
City’s primary vehicle for authorizing new capital projects, the annual CIP list , engages the community
through the budget process and community goal -setting process that the City offers to t he community for
input. The upcoming revision to the 2002 Watershed Enhancement Plan will also be submitted to the City
Council for approval . After this, plan development will transition into implementation of projects. The
completed SRP and the updated Watershed Enhancement Plan will provide a list of prospective projects
that can be moved into the CIP prioritization process (see Section 6.1.1, above) or developed into
proposals for external grant funding.
Although direct consultation with the community does not normally occur in the pursuit of external
grant opportunities, such efforts are typically done in collaboration with other community -based and
supported groups (particularly Central Coast Salmon Enhancement and the California Conservation
Corps ) which help the City to develop these projects and to gain grant funding.
71
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Reducing Stormwater Discharge Contributions to Water Pollution, National Academies Press,
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coastal California streams. Environmental Management 35: 493 -504.
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WATERSHED, California: report prepared for Utilities Department, City of San Luis Obispo, by Thomas
R. Payne & Associates, Arcata, California, April 6, 2004, 37 pp. plus appendices.
Rehn, A.C., Mazor, R.D., and Ode, P.R. 2015 . The Ca lifornia Stream Condition Index (CSCI): A new
statewide biological scoring tool for assessing the health of freshwater streams. SWAMP Technical
Memorandum SWAMP -TM-2015-0002, September 2015, 13 pp.
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Water Pollution Prevention Program, December 2016, 101 pp. Available at : http://ccag.ca.gov/wp-
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Obispo County master water report. Prepared by Carollo Engineers for San Luis Obispo County Flood
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Stillwater Sciences, Morro Bay, California for Coastal San Luis Resource Conservation District, Morro
Bay, California. Available at: http://www.stillwatersci.com/resources/2014SLOinstreamflows.pdf
[Accessed October 31, 2016].
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Stillwater Sciences. 2015. Percolation Zone Study of Pilot -Study Groundwater Basin s in San Luis Obispo
County, California –amended final technical memorandum. Prepared by Stillwater Sciences, Morro Bay,
California for the Upper Salinas -Las Tablas Resource Conservation District, Templeton, California.
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[Accessed October 31, 2016].
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GeoSyntec Consultants, September 20, 2016 , 157 pp. Available at:
http://www.vcstormwater.org/images/Documents/Final_MSWRP_20160920r dx.pdf [Accessed March 10,
2017].
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for Stormwater Retrofits. Ballash, H., primary author, Department of Commerce Publication Number 006,
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(accessed 12/21/2016).
75
APPENDIX
Table A-1. All pubic parcels >0.25 acres, highlighted on Figure 5-1.
Unique
Identifier #
Assessor’s
Parcel Number
Parcel size
(acres)
Overlies
GW basin?
Runoff
class
Pollutant
load class
Near critical
habitat?
1 001-205-014 0.92 yes >0.80 yes
3 002-412-004 0.47 yes yes
4 003-511-022 0.85 yes >0.80 >0.10 yes
5 052-311-017 7.84
6 053-087-018 9.36 >0.80
8 002-321-004 1.11 yes >0.80 >0.10 yes
9 053-051-067 1.81 yes yes
10 003-562-007 0.85
11 003-543-001 3.06 yes >0.80 >0.10
12 002-421-031 0.56 yes >0.80 >0.10 yes
13 003-555-027 1.39
15 002-401-002 0.58 yes yes
16 003-515-001 3.21 yes >0.80 >0.10 yes
18 002-482-026 1.06 yes yes
19 002-482-025 0.83 yes yes
20 003-711-025 3.44 yes yes
21 003-751-005 1.71 >0.80
22 003-742-004 4.54 yes >0.80
23 004-511-018 4.43 yes yes
24 003-739-031 0.41 yes >0.80
25 004-831-005 9.84 yes
27 004-861-005 41.82
28 004-852-023 1.62 >0.80
29 004-826-042 3.56 yes
30 004-852-024 0.36 >0.80
31 004-826-043 0.51 yes
32 004-982-033 4.62
34 004-853-022 0.74 >0.80
35 004-951-014 2.83 >0.80
36 004-951-018 0.68 >0.80
37 004-251-056 7.56
38 053-212-019 1.43
39 053-051-072 1.08 yes yes
76
Unique
Identifier #
Assessor’s
Parcel Number
Parcel size
(acres)
Overlies
GW basin?
Runoff
class
Pollutant
load class
Near critical
habitat?
40 004-933-005 1.17
41 053-071-023 0.55
42 053-071-004 0.39 >0.80
44 053-051-045 48.06 yes >0.80 yes
45 053-071-005 0.66
46 004-591-010 0.51
47 053-131-013 13.95 yes >0.80 yes
48 004-422-033 1.18 yes
49 053-141-012 21.92 yes >0.80 yes
50 053-304-030 3.19
51 053-272-027 1.76 yes >0.80 >0.10 yes
52 053-410-015 0.31 >0.80
53 053-095-033 2.25
54 053-097-048 0.95
55 053-096-022 1.44
56 053-400-031 0.36
57 053-400-030 1.57
58 053-401-019 0.86
59 052-601-010 127.60
60 052-601-009 4.06
61 004-822-045 3.89
62 052-031-001 9.33 yes
63 001-031-028 10.12 >0.80 yes
66 001-181-006 0.90 yes >0.80 yes
67 004-871-005 310.24 yes
68 004-291-008 51.72 yes
69 004-292-041 8.35 yes
70 004-291-007 8.35 yes
71 004-451-013 29.49 yes
72 004-451-019 8.61 yes
73 004-271-032 1.68 yes
74 053-246-041 3.38 yes
75 004-451-021 15.47 yes
77 053-111-055 2.29 yes
78 004-401-031 11.62 yes
79 004-261-085 3.36 yes
80 053-500-002 0.52
81 053-012-012 0.51 yes
77
Unique
Identifier #
Assessor’s
Parcel Number
Parcel size
(acres)
Overlies
GW basin?
Runoff
class
Pollutant
load class
Near critical
habitat?
82 053-111-052 5.29 yes
83 053-116-036 0.89 yes
84 004-422-035 0.81 yes
85 053-502-002 39.90
86 004-431-009 1.01 yes >0.80
87 004-431-028 5.22 yes >0.80
89 053-152-006 9.12 yes yes
90 053-231-038 23.32
92 004-962-022 1.79
93 053-413-049 3.98
94 067-241-032 314.38 yes
95 053-500-003 367.24
96 002-352-002 64.62 yes yes
97 073-341-017 1.51 yes yes
98 003-686-003 21.99 >0.80
99 053-111-058 26.52 yes
100 002-423-006 1.35 yes >0.80 >0.10 yes
101 004-933-010 51.77
112 053-251-056 0.26 yes
113 003-651-015 1.57 >0.80
114 053-152-008 0.34 yes yes
115 053-152-007 3.25 yes >0.80 yes
116 053-152-009 12.85 yes >0.80
118 Cal Poly 427.01
119 Cal Poly 1.16
120 Cal Poly 103.02
121 Cal Poly 237.94
122 Cal Poly 1701.46 >0.80 yes
123 Cal Poly 328.95 yes yes
124 Cal Poly 34.57 yes
125 Cal Poly 5.50 yes
78
Table A-2. Named road segments in the watershed that meet the feasibility criteria and
rate highest in each of the ranked criteria for green street retrofitting , listed in order of
length of “qualifying” segments.
Street name
Combined lengths of
all highest-rated
segments (ft)
Higuera S St 7925
Rougeot Pl 5468
Marsh St 5417
Pacific Pismo Aly 4794
Monterey St 4402
Boysen Ave 3543
N Santa Rosa St 2795
Osos St 2473
Los Verdes 2473
Palm St 2268
Chorro St 1986
Morro St 1960
Granada Dr 1667
Zaca Ln 1566
Meinecke Ave 1537
Perla Ln 1438
Parker St 1426
Walker St 1406
Linda Ln 1371
Archer St 1337
del Sol Ct 1080
Pepper St 973
Carmel St 971
79
Street name
Combined lengths of
all highest-rated
segments (ft)
Court St 970
Encanto Ln 874
Garden St 828
Beebee St 738
High St 706
Los Palos 633
Empleo St 611
Palmmill Aly 484
Empresa Dr 481
Olive St 442
del Oro Ct 356
Monterey Palm Aly 353
Garden Aly 349
Rose Aly 217
Bonetti Dr 197
Villa Ct 139
Vista Ln 116