HomeMy WebLinkAbout10/00/1990, AGENDA AGENDA PACKETS FOR ADJOURNED MEETINGS_
FOP. I?ONTH OF OCTOBER 1990
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G�tiY cry. at o sAn -luis oBispo
Cn EO? f O COUNCIL HEARING ROOM 6 CITY HALL • 990 PALM STREET • SAN LUIS OBISPO
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AGENDA
ADJOURNED MEETING OF THE CITY COUNCIL
TUESDAY, OCTOBER 30, 1990 7:00 P3vL
CALL TO ORDER: Mayor Ron Dunin C
ROLL CALL: Vice-Mayor Jerry Reiss, Councilmembers Peg Pinard, Penny
Rappa, Bill Roalman and Mayor Ron Dunn
PUBLIC COMMENT
(Not to exceed 15 minutes)
Immediately prior to scheduled items, members of the public may address the City Council
on items that DO NOT appear on the printed agenda. Please observe the time limit of 0
three minutes. A speaker slip (available in the Foyer) must be filed with the City Clerk
prior to the beginning of the meeting.
As a general rule, action will not be taken on issues not listed on the agenda. Staff will
generally be asked to follow-up on such items. The Council is interested in hearing from
the public regarding issues or concerns of the community and welcomes your input.
None Received
1. FLOOD MANAGEMENT UPDATE (ROMERO/592 - 1 HR.) F,
Consideration of the Flood Management Report Update and Policy Revision.
RECOMMENDATION: By motion, receive staff report and set a public hearing
to receive testimony regarding Flood Policy and basic approaches to be followed for
flood protection.
ROMERO" FINAL ACTION.• Staff directed to set a public hearing to receive testimony regarding
VOGES"" Flood Policy and provide a supplemental report to respond to Councilman Roalmmn'sTi
request to determine the number of structures that are vulnerable to flooding and identify
the costs associated with flood proofing them. E
Page 1 of 2
Council Agenda October 34 1990
2. PRELIMINARY SEISMIC EVALUATION (ROMERO/462 1 HR.)
Consideration of the Preliminary Seismic Evaluation of City-owned Buildings.
RECOMMENDATION: By motion, 1) receive the report and direct staff to
implement the non-structural repairs through individual department budgets,2)direct
the City Administrative Officer to establish a staff committee to prioritize
recommendations for budget, and 3) implementation of a program for structural
repair of the buildings.
ROMERO* FINAL ACTION 1) Received the report; 2) directed staff to implement the non-
structural repairs through individual departmental budgets, and 3) directed the City
Administrative Officer to establish a staff committee to prioritize recommendations for
budget and implementation of a program for structural repair of the buildings.
COMMUNICATIONS
(Not to exceed 15 minutes)
During the balance of this meeting, any Councilmember or the City Administrative Officer
may informally update the Council of written or oral communications and ask for comment
and/or discussion. State law provides that Council take action only on such matters which
have been noticed at least three days in advance of the meeting unless special circumstances
are found to exist. Formal action or approval is not preferred and such items should be
continued to the next Regular meeting.
Vice Mayor Reiss expressed disappointment in a Council Colleague using the editorial page to
express an opinion regarding a recent a City action.
A. ADJOURN TO CLOSED SESSION TUESDAY, NOVEMBER 6, 1990 AT 4:00 P.M.
Page 2 of 2
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AGENDA �� r` "151
ADJOURNED MEETING OF THE CITY COUNCIL
TUESDAY, OCTOBER 309, 1990 7:00 14
Pam's Agenda
6:00 - 7:00 P.M. CLOSED SESSION to discuss real prop Distribution List
Development, Inc. I. Unpaid Subscriptions: -
(All mtgs.unless o/w noted)
(A light dinner will be available for Councilmembers and nee AIA President
ARC (reg.mtgs:in box)
NASI President
MBIA (in box)
CALL TO ORDER: Mayor Ron Dunin Chamber of Commerce(in box)
—housing Authority(in box)
ROLL CALL: Vice-Mayor Jerry Reiss, Councils=KG0Y //_KanE (until 3/31/91)
Rappa, Bill Roalman and Mayor j -KCPR
KDDB
-KEYT
PUBLIC COMMENT -KJDJ(until 10/30/90)
(Not to exceed 15 minutes) —�Y-/ /'Pac.BelLRt.of_Way
--KVEC
Immediately prior to scheduled items,members of the public n League of Women voters
on items that DO NOT appear on the printed agenda. Plea; Iibra-ryfr-eg7 mtgs:f--cont-desk)
three minutes. A speaker slip (available in the Foyer) must 1 -Mustang Daily •
prior to the beginning of the meeting. �Pac.Gas & Elec.Co.(-reg.mt-gs:)
-- . anning omm. in DD-box}
As a general rule, action will not be taken on issues not liste -Telegram-Tribune
generally be asked to follow-up on such items. The Council y UNOCAL Land & Development Co.*
(*Envelopes provided)
the public regarding issues or concerns of the community andcomcb YUUI LUFUL.
1. FLOOD MANAGEMENT UPDATE (ROMERO/592 - 1 HR.)
Consideration of the Flood Management Report Update and Policy Revision.
RECOMMENDATION: By motion, receive staff report and set a public hearing
• to receive testimony regarding Flood Policy and basic approaches to be followed for
flood protection.
Tic OF CALIFORNIA )
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/o%3�9d Signature I
Council Agenda October A 1990
2. PRELIMINARY SEISMIC EVALUATION (ROMERO/462 - 1 HR.)
Consideration of the Preliminary Seismic Evaluation of City-owned Buildings.
RECOMMENDATION: By motion, 1) receive the report and direct staff to
implement the non-structural repairs through individual department budgets,2)direct
the City Administrative Officer to establish a staff committee to prioritize
recommendations for budget, and 3) implementation of a program for structural
repair of the buildings.
COMMUNICATIONS
(Not to exceed 15 minutes)
During the balance of this meeting, any Councilmember or the City Administrative Officer
may informally update the Council of written or oral communications and ask for comment
and/or discussion. State law provides that Council take action only on such matters which
have been noticed at least three days in advance of the meeting unless special circumstances
are found to exist. Formal action or approval is not preferred and such items should be
continued to the next Regular meeting.
A. ADJOURN TO WEDNESDAY, NOVEMBER 7, 1990 AT 7:00 P.M.
Page 2 of 2
MEOW DATE:
city rSd1 LUIS OB1Sp0 October so
, X990j �
INNaMe COUNCIL AGENDA REPORT
FROM: David Romero, Public Works Director
SUBJECT: Flood Management Report Update and Policy Revision
CAO RECOMMENDATION:
By motion, receive staff report and set a public
hearing to receive testimony regarding Flood Policy and
basic approaches to be followed for flood protection
INTRODUCTION
In 1983 the City prepared two booklets, a Flood Management Report
and a Flood Management Policy. On June 21, 1983 the City Council
made certain environmental findings and adopted The Flood
Management Policy, Standards and an Action Plan (pink book) .
Since 1983 many of the projects designated by the Action Plan
have been completed, others are in various stages of design,
still others have been delayed for various reasons. In the
intervening years the City philosophy regarding floods and flood
protection has altered somewhat, and staff has been directed to
restudy the basic approaches to flood protection with the aim of
eventually adopting a new Flood Protection Policy and Action
Plan.
PURPOSE
The purpose of this report is to provide an update of waterway
improvement work conducted since 1983, and to initiate a dialogue
which will lead to adoption of a new action plan to protect
against flood damage. This is to be done while keeping in mind a
primary goal of preserving the natural beauty and character of
the creek system.
SUMMARY COMPARISON
Key to a decision to change the approach to flood protection is a
clear understanding of the 1983 approach as compared to the
approach recommended in this report.
Several studies have shown that after the City has done all
that it can in creek management, the city will still flood
in major storms. The 1983 approach called for widening of
most of the major creeks to handle flows anticipated in
design storms. The approach recommended in this report
calls for a combination of partial retention upstream of the
city and a smaller creek widening below the confluence, with
no widening of San Luis Creek above the confluence.
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►�GiIIIIIi�Pp ����U city of San tuts ogIspo
AWrZo COUNCIL AGENDA REPORT
Flood Update
Page Two
BACKGROUND
In the 1983 Flood Management Report certain background
information was presented, some of which is summarized and
updated as follows:
a) The major creek system includes San Luis Obispo Creek,
Old Garden Creek, Stenner Creek and Prefumo Creek, with
many smaller tributaries, most of which are unnamed.
b) The major creek system contains a total of 12..6 miles
within the city limits.
c) Approximately 92% of the creeks within the community
are privately owned, approximately 8% are publicly
owned. Approximately 50% of the privately owned creeks
are within drainage easements, due in large measure to
the City efforts in recent years to acquire easements.
d) The total drainage basin at the downstream city limits
is 42.6 square miles of which 9.5 square miles lies
within the city limits. The 100 year floodplain
within the city is 1.5 square miles (0.4 square miles
of which are within Laguna Lake) .
e) The largest floods of recent history occurred in 1969
($1,628,000 damage) and in 1973 (around $4,000,000
damage) .
ACTIONS SINCE 1983
In 1983 the City Council adopted a flood management policy,
standards and an action plan. In adopting these the City Council
attempted to achieve a balance between a) full flood protection,
resulting in major alteration to the creek environment, and b)
minimal flood protection, with preservation of existing creek
amenities.
The flood design criteria recommended by staff and adopted by the
Council was based on the existing 40 year storm capacity of the
culverts crossing 101 into and out of Cuesta Park and the 40 year
storm capacity of the undercity culvert. By using these
structures as a design basis, the City could achieve a relatively
cost effective level of protection for downtown. Minor creeks
were to be designed on a 10-25 year storm basis, Old Garden Creek
on a 25 year storm basis, San Luis Creek above the confluence on
a 40 year storm basis, and Stenner Creek, Prefumo Creek and San
Luis Creek below the confluence on a 50 year storm basis.
' 4 -
city of san lues oBispo
jSMaMe COUNCIL AGENDA REPORT
Flood Update
Page Three
In order to achieve a balanced capacity on each of the creeks,
staff submitted a prioritized list of restricted capacity (tight
spots) on each of the creek systems. Since 1983, the City has
carried out an aggressive program to correct these tight spots.
Of the 26 tight spots listed, 17 have been corrected, 5 are in
some stage of design, and 4 have had no action.
Seventeen street drainage improvement projects were listed. Of
these 14 have been completed, 1 is ongoing annually and 2 have
had no action.
Five minor waterway modifications were listed. Of these 3 have
been completed, 1 is ongoing annually and 1 has been corrected by
improvements installed in a nearby subdivision.
Nine major waterway modifications were listed. None has been
completed, though a number of right-of-way easements have been
acquired and one project (San Luis Creek---Bianchi Lane bridge to
downstream of South Street) has been designed. A second project
(San Luis Creek, sewer plant to Prado Road) will be completed as
part of a subdivision now in process of obtaining approvals.
Improvements completed on San Luis Obispo Creek to relieve tight
spots have resulted in increased capacity at 9 locations as shown
on Exhibit A .
The major uncompleted work remaining from the 1983 report relates
to enlarging San Luis Obispo Creek to a 50 year capacity between
the sewer plant and the confluence, and enlarging San Luis Creek
to a 40 year, and Stenner Creek to a 50 year, capacity from the
confluence to Nipomo Street.
RECENT STUDY (Exhibit B - Summary of Report)
In October 1987 the City Council requested a City study of the
efficacy of upstream detention of flood waters, thus providing a
more cost effective solution to flood protection and resulting in
lesser damage to the creek environment. The City hired James
Schaaf, president of Schaaf & Wheeler, to conduct the study.
Mr. Schaaf studied 7 alternative sites on San Luis Obispo Creek,
3 alternative sites on Stenner Creek, various dam heights at each
of these locations and various combinations of alternatives, a
total of 31 possibilities overall. Mr. Schaaf studied detention
dams (with a hole in the bottom, thus allowing some water to pass
through) , modification of culverts and flood diversion dams
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�� �►IIII(1�►� ►����I city of San tins osrspo
COUNCIL AGENDA REPORT
Flood Update
Page Four
leading to off-channel storage. Of all the alternatives, none
had a positive benefit-cost ratio*. The best alternative was a
56' high dam somewhat upstream of U.S. 101 above Cuesta Park, at
a site previously reviewed by the Corps of Engineers. This
facility had a benefit-cost ratio of 0.80. This design would
allow a 40 year storm to pass and would require that the entire
downstream creek system be brought up to that capacity and more
as one goes further downstream. This closely approximates the
policy adopted in 1983.
Schaaf's closing statement in the conclusion portion .of the
report is as follows:
With no immediate prospect of providing some flood
protection by utilizing upstream detention, the City
will have to concentrate its flood control efforts on
improving channel capacities through the populous area to
minimize the flooding problem and encouraging both the flood
proofing of individual structures and the individual
purchase of adequate amounts of federal flood insurance.
Schaaf's basic approach to the study was to construct a detention
dam large enough to retain a 100 year storm while releasing a
limited flow (25-50 year) through the dam and into the city creek
system.
ALTERNATIVE APPROACH
One of the primary reasons for the study was to determine whether
some upstream detention would allow the City to minimize creek
widening within the community. With this goal in mind, staff has
conducted considerable additional analysis, with a slightly
modified approach, to see whether some alternative might better
meet the goal and at the same time be cost effective. Staff's
approach was to construct a dam designed for minor storms to pass
through without restriction, to partially restrict the flow for
intermediate and major storms, but to be overtopped by major
storms. This design results in a lower dam, but more
importantly, provides some level of downstream protection for all
significant storms. Preliminary calculations indicate a good
*A positive benefit-cost ratio indicates that benefits to be
derived from the project are greater than the cost of doing the
project.
�IN11�i; IlfB���►i ����jl city of san tuts oBispo
niis COUNCIL AGENDA REPORT
Flood Update
Page Five
possibility of obtaining a favorable benefit/cost ratio for the
dam (Exhibit C) . Construction of such a dam would not eliminate
the need for creek widening in San Luis Creek, particularly below
the confluence. However required widening would be minimized,
reducing acquisition and construction cost and environmental
damage.
DISCUSSION
All of the dam alternatives require property acquisition, flood
easement acquisition, an environmental impact study and funding
of a fairly large capital project so it can be constructed at one
time. All call for some fairly large magnitude of flow passing
on through the city creek system.
Of all the dam alternatives, the staff approach (a dam with a
small, perhaps 8 ' diameter, opening in the bottom) is most cost
effective (B/C ratio 0.95) . The dam would restrict flows
entering the city on San Luis Creek and the opening would be
sized so as to meet the capacity of the existing creek through
the downtown. Except for tight spots, San Luis Creek through
town could remain in its current natural state.
Below the confluence, where unrestricted flows from Stenner Creek
and Old Garden Creek join San Luis Creek, the dam will restrict
flows by approximately 23%. The remainder flow, while
substantially reduced, can only be carried within the creeks
below the confluence if the creeks are widened. Although the
width of widening would be reduced by the dam, virtually all
portions of the creek would require widening. Since most of this
area of the community is not densely developed, it appears
practical that this portion of the creek could be widened without
excessive cost or excessive environmental damage.
This has led staff to the conclusion that the most feasible means
of providing flood protection for the community involves 3
concurrent programs a) development of a detention dam on San Luis
Creek above the city, b) elimination of tight spots in each
waterway so as to achieve a balanced hydraulic capacity on each
creek, and c) widening of San Luis Creek from the confluence to
the southerly city limits. These conclusions were presented to
the Zone 9 board at the December 28, 1989 meeting and unanimously
concurred with.
� �►i►�iIIII��I��n ►9�IIIi city of San tins OBISpo
ONGe COUNCIL AGENDA REPORT
Flood Update
Page Six
FLOOD MANAGEMENT POLICY
In 1983, the Council adopted a Flood Management Policy (Exhibit
D) . Because the policy is so basic to updating the entire
report, staff requests that the Council review, modify it as
desired and adopt or readopt a policy. Staff concurs with the
current policy with the minor amendments shown.
ADDITIONAL DISCUSSION
In recent years, the citizens and the Council have expressed a
desire to develop a trail system along the creeks and for
development of additional parks and open space. Development of a
dam above the city would necessitate acquisition of property for
the construction of the dam and flood area.. It would also be
highly desirable to acquire the remainder property between the
dam and the culvert leading under 101 (site of old reservoir and
training facility) . Because flooding of all of this property
would be rare and only for short time intervals, all parcels
could be developed to whatever recreational purpose was desired
by the city. This is an especially beautiful riparian area.
With a widened San Luis Creek between the confluence and the
southerly city limits, it would be quite feasible to incorporate
a trail system into the facility.
Both flood control measures therefore, could and should serve a
dual purpose for the community, and the existing riparian habitat
could largely be preserved.
FISCAL IMPACT
Property acquisition and improvements are estimated at $2.2
million for the upstream detention dam. Tight spot improvement
for San Luis Obispo and other major creeks is estimated to cost
$0.5 million. Property acquisition below the confluence is
estimated to cost $4.2 million if it must be purchased, though
most of it may be exacted as properties develop. Creek widening
below the confluence is estimated to cost $8.5 million, though
much of it may be required as property develops. All figures are
exclusive of costs to develop trails, recreational facilities, or
environmental mitigation.
���� ►I�IIIIIfI�p �N)il city of San lues OBISPO
COUNCIL AGENDA REPORT
Flood Update
Page Seven
ALTERNATIVES
A) Do Nothing Alternative
The city could determine that since none of the flood control
projects are cost-beneficial, the city should not use taxpayers
funds for improvements.
Advantages
The city would save millions of dollars in direct expense
and untold staff hours. Creeks below the confluence would
remain at their current width.
Disadvantages
Without some positive improvement to the creek system,
substantial rains will result in major flooding of downtown
and lower Higuera, similar to that which occurred in 1969
and 1973. The benefit-cost formula does not take into
account human suffering, risk to life, or major
inconvenience when the city is incapacitated by, and
recovers from, a heavy storm.
City would lose an excellent opportunity to develop a creek trail
system, and recreation facilities at the dam site.
B) The 1983 Plan Alternative
The City could determine that the current approach to .flood
protection should be followed. Current approach calls for no
upstream dam but widening of all creeks to sufficient capacity to
handle the design storm.
Advantages
Major one-time capital cost of acquiring property and
constructing the dam can be avoided.
Disadvantages
Most of San Luis Obispo Creek through the city would have to
be widened (or if not widened, lined) to accommodate design
flows. Because of additional creek widening compared to the
upstream detention dam approach, property acquisition
problems are compounded and total costs are greater.
���»h►�►Illlf�p� �► �j1 city of San 1Uis OBIspo
M"Mi COUNCIL AGENDA REPORT
Flood Update
Page Eight
C. The Upstream Detention Dam, together with minimal widening on
major creeks. Alternative (staff recommendation)
Advantages
1) The upstream detention dam recommended by staff provides
the most cost-effective solution of all the alternatives
studies.
2) Riparian habitat upstream of the city would be purchased
and developed for park purposes.
3) San Luis Creek upstream of the confluence would not have
to be widened, thus preserving existing habitat.
4) San Luis Creek downstream of the confluence would be
widened by a lessor amount than under the current plan, thus
minimizing damage to the riparian habitat and costs.
5) A trail system can be developed in conjunction with
widening below the confluence.
6) Citizens within the community will be protected when all
improvements are completed.
7) If desired, the upstream detention dam can be managed so
as to retain some water at the end of the rainy season which
can then be released during the summer to enhance the creek
habitat.
Disadvantages
1) Acquisition of property and development of the dam will
require a lump sum expenditure of $2.2 million, which may
create funding problems.
2) Widening of San Luis Creek below the confluence will
still be required.
3) Construction of the dam and widening below the
confluence will create environmental damage which will
require some time to completely mitigate.
4) There is always some risk of dam failure, though the dam
would be empty or would retain only a small amount of water
most of the time.
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� � uuili(II'�Ip ►���pl city Of San LUIS OBISPO
Wi% COUNCIL AGENDA REPORT
Flood Update
Page Nine
RECOMMENDATION
Staff feels that the pain and suffering and the risk to life and
property during flooding of downtown is a dominant consideration,
of much greater importance than a judgement based only -on a
benefit-cost ratio. Staff feels that the best answer lies in the
recommended program, which after it is carried out over a number
of years, and completed, will result in a high level of flood
protection for the city. If the program is conducted sensitively
the natural creek environment will be protected, and the city can
develop a trail system along much of the creek and a major
recreation facility at the dam site.
Specifically, staff requests the following Council action.
A. Reaffirm Flood Management Policy
B. Direct staff to pursue flood control studies and
reports with the following as basic approaches:
1) Development of a detention dam upstream of the city
on San Luis Creek following staff concept of
restricting all flows greater than a 10 year storm.
2) Eliminate tight spots in each of the City's
waterways, so as to achieve a balanced design which
will handle design flows.
3) Widen San Luis Creek from the confluence to the
southerly city limits to handle design flows. This
widening will be accomplished as opportunities present
themselves, based on an adopted creek widening plan
line and creek widening policy. Most of the
acquisition and widening would be conducted as
properties are developed.
4) Incorporate in all waterway improvements, where
feasible, trails, retention of riparian habitat and
other amenities to create an attractive environment.
Because of the major implications of this action, staff
recommends that the matter be set for public hearing.
Attachments: A) Tight Spot Creek Improvements B) Summary-Schaaf
C) Staff Study of Upstream Detention Alternatives
D) Flood Management Policy
NOTE: Copy of the Flood Management Policy (pink book) is
available in the Council reading file.
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SUMMARY — se e7
One strategy for reducing flood damages in San Luis Obispo is to create one
or more upstream detention facilities. The theory behind these facilities_
is that they would hold back. the peak portions of flood flows and release
them slowly enough to reduce or prevent downstream flood damage.
These detention facilities could be one of two types. The first would be a
dry dam. This would essentially be an embankment made of compacted earth
with an outlet structure in the bottom which would allow a limited amount of
flow to pass. The dry dam would also have a concrete spillway so that in
the event of an extremely large flood the dam would not be overtopped. This
type of detention facility would look similar to the U.S. 101 culverts on
San Luis Obispo Creek near Cuesta Park. In most cases the embankments would
be higher than the approximately 35-foot high embankments and the outlet
works smaller than the 19-foot by 15.25-foot arched culvert under each U.S.
101 crossing. There is very little if any permanent pool behind these
culverts under U.S. 101. This would be similar for the dry dam detention
facilities.
The second type of detention facility would be a diversion with off-channel
storage. This type of facility would consist of a diversion structure on
the creek, a transmission facility usually consisting of a pipe line or an
open channel and a dam which forms a reservoir not on the main stem of the
creek but on a smaller branch. This type of facility would be similar to
the diversion structure, pipe line, -open channel, dam and reservoir on
Stenner Creek operated by Cal Poly as a water supply facility. However,
because so much water has to be stored to reduce downstream flooding, the
dams considered in this investigation would be significantly higher than Cal
Poly's and the pipe line and the open channel would need to be capable of
handling a much larger capacity of flow than the existing pipe and channel.
A number of different sites above the City were selected for consideration
of upstream detention of flood flows. On Stenner Creek. three different
alternatives were considered. These consisted of a dry dam in the narrow
canyon upstream of the railroad crossing, and two diversions with off-chan-
nel storage. On San Luis Obispo Creek eight different alternatives were
considered. .These consisted of six one-facility alternatives, one three-
facility alternative and one four-facility alternative. A two-facility
alternative was not feasible-.
The six one-facility alternatives consisted of a dry dam located immediate-
ly upstream of the U.S. 101 crossing which is just upstream of Cuesta Park,
a modification to the existing culvert under U.S. 101, a dry dam located at
the Corps of Engineers' site considered in the 1987 feasibility study, and
three diversions with off-channel storage. Two of the diversions were for
high flows only. The shorter of these two diversions had to convey water
diverted from San Luis Obispo Creek 5,000 feet to a reservoir formed behind
a dam built near the mouth of the canyon just to the north of Reservoir
Canyon. The longer diversion had to convey water diverted from San Luis
Obispo Creek a distance of 8,000 feet to reach the reservoir. The longer
diversion had a steeper slope than the shorter diversion. The low flow
diversion was 5,000 feet long.
Schaaf 6 Wheeler
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The three-facility alternative consisted of a dry dam on San Luis Obispo
O Creek just upstream of the Reseivoir Canyon Road crossing, a dry dam in the
canyon just to the north of Reservoir Canyon and a larger dam on Reservoir
Canyon. The four-facility alternative consisted of the same three dry dams
as for the three-facility alternative with the addition of a dry dam on San
Luis Obispo Creek along the. Old Cuesta Grade Road. The three-facility and
the four-facility alternatives were investigated to determine if there was
any merit to considering smaller but more numerous dams as a flood damage
reduction strategy.
The principal method used to evaluate the alternatives was a benefit to
cost ratio. In this method, if this ratio of benefits to costs is greater
than or equal to one, then the benefits of constructing the alternative
outweigh the costs. Conversely, if the ratio of benefits to costs is less
than one, the'costs outweigh the benefits.
Benefits considered were flood damages prevented. These were updated from
the 1977 Master Flodd Control and Drainage Plan even though some structures
in the flood plain have been flood proofed since the 1977 report. No new
flood damages were considered as all new construction must meet City stand-
ands requiring that structures be built so as to be free from flood damage.
Water supply benefits were also considered, particularly for the diversion
alternatives. The benefits for the high flow diversions proved to be quite
low principally because the diversions did not operate until the flow in the
main creek reached a particular threshold value like the 50-year or the 40-
year peak flow. Thus there would not be too many times that such a facility
would be expected to be used and not too much water supply would be expected
G. on the average. The low flow diversion alternative would provide much more
significant benefits. however, these were not sufficient to make the total
project achieve a benefit to cost ratio greater than one.
While the benefit to cost ratio is one important consideration in the
analysis of alternatives, it is also important to consider other aspects
such as financing. Detention facilities generally require a large, initial
outlay of money to design and construct the facility as opposed to some
channel enhancement works which may be constructed incrementally as funding
allows. Thus detention projects which have more benefits than costs may be
more difficult to fund than projects which can be implemented over a period
of time.
The results of the benefit to cost ratio analysis indicated that the best
alternative was the dry dam at the Corps' site. This alternative would
limit the flows downstream of Cuesta Park to a rate approximately equal to
the capacity of the under-city culvert. The benefit to cost ratio, however,
was only 0.80 indicating that the costs would outweigh the benefits. The
costs included construction costs, right-of-way costs, and operations and
maintenance costs but did not included any costs for environmental mitiga-
tion.
Even with this dry dam in place, there would still be potential flooding
along San Luis Obispo Creek downstream of the Stenner Creek confluence. For
Oexample, given this dry dam with a release rate which matched the capacity
of the undercity culvert, the 100-year peak discharge downstream of the
Stenner Creek confluence would be reduced from 13,700 cfs to 12,200 cfs.
Schaaf Wheeler ii I 'Q
I i �
Therefore, significant channel work would still be required to provide even
a 50=year level of protection in this reach of San Luis Obispo Creek. Also -
some improvements upstream of Stenner Creek would still be needed to elimi-
nate the remaining bottlenecks -and very low capacity sections.
When considering the one-facility versus three-facility and four-facility
combinations, the costs went -up as the number of facilities increased.
Placing dams higher up in the. watershed meant that the height of the dam had
to increase in order to achieve a given level of storage and thus the facil-
ity became quite costly.
Of all the flood damage mitigation plans over the years, the alternatives
with the highest benefit to cost ratios always includedsome upstream
detention facility. However, none of the previous studies found a project
with a ratio greater than or equal to 1.0.
Given the low benefit to cost ratio, there does not appear to be an
immediate prospect -of providing flood protection by usinyipstream detentiori.
The City can still pursue a reduction in flood damages fhougb increasing
channel capacities through the City, by encouraging flood proofing of exist-
ing structures, and by conforming to the guidelines of the National Flood
Insurance Program.
The concept of an upstream detention facility could be reconsidered if the
City found another substantial benefit which could be obtained at the dry
dam or in the reservoir area such as a large recreational use which could
withstand periodic inundation. In particular, if the City purchased large
amounts of land particularly in the Alternative 2 pool area for other �.
purposes, it might be appropriate to reconsider the concept of a dry dam at
that site.
Schaaf & Wheeler iii
B - 3
oMEMORANDUM
PUBLIC WORKS DEPARTMENT
ENGINEERING DIVISION
Date August 22,1990
To David F. Romero, Director of Public Works
From Wayne Peterson, City Engineer
Subject Alternative Up-stream Detention Systems
Two alternate scenarios to Jim Schaaf's proposals for
upstream detention have been explored by staff.
First, is to detain all creek flows above the City and to
provide a controlled release that results reduces flows in San Luis
Creek to the confluence so there is no flooding during a 40 year
storm or smaller storm. Storms that are larger than the 40 year
design standard would cause increasing flows and downstream
flooding would occur. The apparent result would be similar to that
which would have resulted if the creeks channel had been improved
to handle a 40 year storm all the way to the confluence. An added
advantage of the upstream retention over- the creek improvement is
that the creek below the confluence will also see somewhat less
O water .in all storms and will require less widening to handle a 50
year design storm.
The dam structure would be designed to provide a .continual
release through a pipe at a high rate so that when the storm ends
the level of water would rapidly drop leaving no water stored
behind the dam. The weir overflow of the dam would should be broad
so that when the 40 year flood is exceeded little additional water
is stored behind the dam. This reduces the height of the dam and
the cost. Some reduction in flood flow below the dam is still
achieved because the dam must store some water above the crest of
the spillway for the spillway to work.
This concept would require no manual control at the dam. In
the case of storms exceeding a 100 year event there would be little
benefit.
Technical Information
The release rateup to a 40 year design storm would be
throttled to appear to the downstream area as a 10 year storm and
all of the creek to the confluence would contain the water. A 100
year event would be equal to a 50 year storm at the confluence.
A second scenario that has been suggested is to build the dam
with a very small release system at the bottom of the dam and a
larger release systems higher up on the face of the dam. This dam
would not release all the water stored immediately after a storm.
C It would store enough water so as to be able to release it
2 �
throughout the summer. This system might help recharge downstream J
water tables during the summer. (While the storm retention would
be in the magnitude of 900 to 1000 acre feet, this retention for
later release would be in the magnitude of 400-500 acre feet in
order to provide a continuous 1 cfs flow in the creek during the
summer and early fall. ) This dam would have a very small pipe
releasing water from the bottom of the reservoir area, a larger
pipe similar to the first scenario releasing water from a higher
level during and after storms and a very wide spillway as in the
first scenario releasing flood flows for large storms.
Location of Dams
1) Two different retention sites were considered for the two
scenarios. The first site is on San Luis Obispo Creek directly
above the City's police shooting range. This is a site that the
Corps of Engineers considered in their analysis as did the Nolte
Report.
The dam for scenario one would be about 60 feet high and have.
a spill way at 48 feet. An 8 foot diameter pipe would be the low
flow outlet. The following chart indicates the depth of water in
the dam for each storm and the flow in the creek at the confluence
with Stenner Creek.
Size Depth of Q in SLO cK Q in SED CK
of Storm Water in Dam Above Conf1. below Confluence
25 year storm 38 ft. 2082 cfs. 4796 cfs.
40 year storm 45 ft. 2541 cfs. 6366 cfs.
50 year storm 51 ft. 2831 cfs. 7461 cfs.
100 year storm 55 ft. 5550 cfs. 10464 cfs.
Storage behind the two 101 culverts is almost nothing for all but
the 100 year flows. A 60 foot high dam will prevent overtopping
by a standard project flood.
2� An alternate to the dam on the main thread of San Luis Obispo
Creek is two dams on the tributary called Reservoir Canyon and the
adjacent branch entering from the east of Reservoir Canyon.
Reservoir Canyon is very narrow and has little capacity. For this
alternative to work most of the flow from Reservoir Canyon needs
to be diverted into the adjacent creek or the dam in Reservoir
Canyon needs to be exceptionally high. This diversion must be at
a high flow. The following chart shows the advantages of these
retention with two different release rates. As can be seen, even
with the lowest release -rate the flows in San Luis Obispo Creek at
the confluence are higher than the flows resulting from the main
stream retention dam.
O3
100 cfs release 400 cfs release
Cuesta Confl. Cuesta Confl.
cfs. cfs. cfs. cfs.
10 YEAR 854 1145
25 YEAR 1617 2160
40 YEAR 2261 3021 2458 3380
50 YEAR 2722 3637
100 YEAR 3873 5079 4129 5377
Storage for 400 cfs release at 100 years is 900 ac-ft and 427 ac-
ft at 40 years. Storage for 100 cfs release at 100 years is 1113
ac-f t. The height of each dam for the lower release rate is 5o
feet in Reservoir Canyon and 56 feet in the East Fork of Reservoir
Canyon Creek.
Attached are two maps showing the proposed dams and the areas
that would be flooded as a result of their construction.
Dam Size to Provide 1 cfs summer release.
In order to provide the additional storage necessary to allow
for summer releases or for water supply the dams shown would need
to be about 10 to 15 feet higher than those for just flood
O protection. In addition their may be more stringent construction
requirements for dams which store water throughout the year as
compared to those that are only holding water a short time. This
is an area which has not been investigated.
An alternate way to provide for the summer release program
would be a managed gate on dam proposed in scenario one. This dam
would be the same size but would have a gate across the outlet pipe.
which would allow the release rate to be lowered or stopped. In
this way the dam could be made to store water year round. Most
really large dams operate this way. The operator would need to be
aware. of weather conditions and lower the water prior to any storm
that may generate flows requiring retention.
BENEFITS
DUE TO
PREVENTION OF FLOOD DAMAGES
Location: Upper San Luis Obispo Creek
Location Rate Costs Benefits B/C
SITE 8 ft. pipe $2.2 Million $2.1 Million 0.95
ON MAIN
STREAM
RESERVOIR 100 CFS. 3.8 Million 2.0 Million 0.53
CANYON
400 CFS. 3.0 Million 2.0 Million 0.53
- 1
4
The additional cost to provide added storage to allow a summer
release of 1 cfs was also investigated. The estimated additional
cost due to the higher dams at either site is $1 Million.
Cost figures are calculated using information in Schaaf Is
report. Benefits are calculated in the same manner as they were
in Jim's report also. Jim's report of cost and benefit analysis
is based upon methods used by the Corp of Engineers and does not
include costs of ecological requirements or the emotional impact
on people of a flood. Additional geological studies should also
be of the various sites.
Advantages and disadvantages of these two scenarios
Scenario One-Only Flood Retention and floodwater reduction
Advantages
1. Smaller lower cost facility.
2. Less water stored during a large flood.
3 . Less area inundated and for a shorter period of time.
4. Maybe simpler dam construction.
5. No standing water to manage during the summer.
6. Entire flood plain of dam can be used for recreation
when not being used for flood control.
Disadvantages O
1. Possible problems with water rights claims.
Scenario Two-Flood Retention and summer release.
Advantages
1. A water feature that could be worked into a recreation
area.
2. Potential water recharge for downstream basins.
3. May gain more support since it will provide benefit
every year and not just during floods.
Disadvantages
1. More costly and complicated alternative with either
operating system.
2. Possible problems with water rights claims.
3 . A managed outlet may be less costly due to a lower dam
structure and a smaller flooded area but would require
staff management and decisions as to the size of the
pool to maintain during various times of the year in
order to maintain a safe facility..
e- - 41
O
5
4. Concern for safety of downstream persons due to a
permanent upstream retention of water.
Recommendation:
Engineering Staff recommends that first scenario be further
explored with the option of gating the outlet pipe to maintain a
minimal pool for possible summer release. Staff does not recommend
that.the dam size be enlarged for the simpler operation due to the
extraordinary extra cost.
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SECTION II. Flood Management Policy.
A. In April 1983 a comprehensive flood management report was
prepared by staff and presented to the Council. This report
included valuable background information and provided a framework
for the City's flood management policy and program.
B. Policy Objectives. It shall be the policy of the City
that waterways and adjacent lands be generally managed to:
1. Maintain the creeks in a natural state to the max'
emtentasale;
2. Prevent the loss of lifettit3ti3e pr+azy.„da; ±e
from flooding; and
a . Hininise damage tram flooding.
Cres'k aiterat"�.ur� s'ba13: � �..3se �t1�o��si�;. ,a ..�n z�stoze
oaused 'by tie �nt��itiz�x� s�� tie �xe+e°� �:r�x �3..x�rx ��"lr�wM err
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s� :t`hout alte�rixxg t �>�zeek�.,_�ar �a��h�,,.c+ +exw!�sa be
4 . Projects designed to alter a creek shall consider solutions
which result in as natural a creek corridor as is possible.
C. Storm Design Capacities. Pending focused environmental
evaluations, the following storm design capacities are adopted to
contain the creeks within their banks (with WN”
freeboard) ;
1. San Luis Creek - 40-year storm to confluence; 50-year
storm below confluence;
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2. Old Garden Creek - 25-year storm;
f�Jl 3. Stenner Creek - 50-year storm;
4. Prefumo Creek - 50-year storm; and
5. Other Minor Waterways - 10 to 25-year storm dependent on
watershed area.
D. Development in Creek Area. New development in waterway
areas shall not be permitted to encroach in any manner which
would diminish or otherwise constrict the specified storm design
capacity of the waterway in that area '`" oipvs
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ccxtxary toile abv sted$ icGes. New development projects
in waterway areas, including governmental projects, shall be
required to participate equitably in waterways "p
to attain the storm design capacity of the waterway
at the project location.
E. City Waterway Program Emphasis, The City shall
undertake, on a planned basis and subject to funding, integrated
structural and non-structural waterway alteration programs which
shall include:
1. Annual, environmentally-sensitive creek maintenance;
2. Removal, from the creeks, of obstacles which inhibit
natural flow; and
3. Enlargement of creek channels, to attain specified storm
design capacity standards, only when no other alternative
is found to be feasible.
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The City shall actively seek to obtain easements and/or
ownership for 'l3:C; creek access, maintenance and construction
whenever possible and appropriate.
Joint creek improvement projects
aa3yj` shall be encouraged by the City when related to
proposed development in areas adjacent to waterways.
Th e•L L 1 1 develop
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0 - 3
MEEnNG DATE:
�►► ►�Ilflpp q��U city of San lues OBISpo "Oct. 0. 1990
COUNCIL AGENDA REPORT
FROM:
David F. Romero, Public Works Director
Wayne A. Peterson, City Engineer
SUBJECT:
Preliminary Seismic Evaluation of City-Owned Buildings
RECOMMENDATION:
Staff recommends that Council, by motion: 1) Receive the report,
2) direct staff to implement the non-structural repairs through
individual department budgets, and 3) direct the City Administrative
Officer to establish a staff committee to prioritize recommendations
for budget and implementation of a program for structural repair of
the buildings.
BACKGROUND:
This past spring a management meeting was held to discuss the need to
evaluate the ability of City-owned buildings to survive an earthquake.
The Public Works Department was requested to seek a professional
consulting firm with excellent qualifications to review the principal
City-owned buildings and to make recommendations regarding their
condition and need for repair.
Following the Purchasing Manual procedures, H.J. Degenkolb Associates,
Engineers was hired to conduct the review. The consultant will be at
the October 30th meeting and will make a brief presentation on each
building and will answer questions.
Results of Report Summar►-
Twenty-nine city-owned buildings have been reviewed, both for
structural and non-structural earthquake related problems that may
cause injury, loss of life, or loss of use of the facility. Thirteen
of the buildings provide essential services--one is rated a high risk
to life safety (955 Morro Street) , two are rated a moderate risk to
life safety (fire station #f2 and city hall) , and one is rated a low
risk to life safety (fire station #3) . The remaining buildings are
rated minimal or conditionally-minimal risk.
The remaining 16 buildings provide non-essential services. These
buildings are occupied. One (the County Museum) is given a high risk
to life safety, three (Recreation Center, Recreation Administration
Building, and Black Adobe) are given a moderate risk to life safety,
and three (the Art Center, Senior Citizens Center and Jack House) are
given a low risk to life safety.
The report also rates essential services buildings as to the extent of
damage that may be sustained from an earthquake by estimating the
number of days following an earthquake before they could be reoccupied.
The results range from greater than 90 days for 955 Morro Street, City
city of San Luis OBISPO
WOrme COUNCIL AGENDA REPORT
Stesmtc Evaluation
Meeting of October 30, 1990
Page Two.
Hall and Fire Stations 12 & 13, to less than two weeks for fire station
#4, the Water Treatment Plant and Corporation Yard. Estimates for
remedial strengthening of the buildings were made for those buildings
that were considered life threatening.
NOTE: Fire Station #1 was not included within this evaluation, since
previous studies had already determined its unsafe condition, and the
decision has already been made to abandon the station.
Cost Impact:
The cost for non-structural work has not been estimated. The costs
should be small and the types of repairs should become a standard, a
way of life, i.e. , water heaters should be strapped to a wall, file
cabinets should be fastened together or to walls, hanging lights should
be cross-braced.
The estimated cost for structural repairs is $1.3 million. The real
cost may be more or less, based upon complete engineering and contract
costs. Some of the structural work may be avoided by abandoning the
building. Early completion of the City Hall annex will mean 955 Morro
Street can be demolished, saving over $300,000. All remodel projects
should consider and include appropriate repairs as a part of the
project.
Direction:
Staff and consultant recognize that the problems itemized in the report
are at two different levels. The easiest problems to address can be
handled by staff with generally limited impact on budget. These
problems relate to non-structural improvements and corrections within
the buildings, such as modifications to office furniture, attachments
and connections to water and space heaters, and attaching restraints to
hanging ceilings, lights and other similar types of fixtures. These
modifications are of such a minor nature that they can be absorbed
within departmental budgets. Staff recommends that. Council direct
individual departments to address these Problems within their budcets.
The more complex level of problems to be addressed relate to the
structures themselves. Depending on the building type, significance
and priority, these problems may be addressed by hiring a structural
engineer to design a repair system or to further investigate the
problem for a more in depth evaluation than what has been done by this
consultant.
����� ►�illlll�i� ►���U city of San tuts OBISPO
COUNCIL AGENDA REPORT
eismic a ua ion
Meeting of October 30, 1990
Page Three.
Inasmuch as the structural repair of the buildings will be expensive,
will involve prioritization between departments, and a certain amount
of expertise, staff recommends these be considered by a city-wide staff
committee and the repairs scheduled within a non-devartmental part of
The budget.
RECOMMENDATION:
Staff recommends that. Council, by motion: 1) Receive the report, 2)
direct staff to implement the non-structural repairs through individual
department budgets, and 3) direct the City Administrative Officer to
establish a staff committee to prioritize recommendations for budget
and implementation of a program for structural repair of the buildings.
Report from Degenkolb is available
in the Council office for review
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