HomeMy WebLinkAbout02/19/1991, 4 - LAGUNA LAKE MANAGEMENT SAME .REPORT AS PREVIOUSL' :NT OUT 2/5/91 /6
W�I�Illn�l^'�^'�NIII lu,lll MEETING DATE:
II IIIrIN�lllul
city Or 1 !�� lu,s OB's� ITEM NUMBER:
COUNCIL AGENDA REPORT
FROM: Dave Romero, Public Works Director C
SUBJECT: Laguna Lake Management
CAO RECOMMENDATION:
By motion, direct staff:
a) to proceed with plans and specifications for removal of
material from the delta (Alternative a) . Funding will be
considered in the 1991-93 budget.
b) to expend no further effort in pursuing re-creation of inlet in
the lake arm (Alternative d) ,
c) regarding Council desires concerning long term viability of the
lake.
BACKGROUND:
In 1982, the City Council adopted the Laguna Lake Management Program.
The program called for four immediate actions on the part of the City
and three alternative actions (Exhibit A-1 and A-2) . The immediate
actions called for are as follows:
1. Purchase of a mechanical weed harvester for clearing appropriate
portions of the lake.
2. Periodically remove accumulated sediment from the Prefumo inlet and
delta.
3 . Construct a temporary log dam approximately one foot in height at
the downstream end of the Madonna Road culvert.
4. Establish a monitoring program to document the effects of the
actions listed above and also provide additional data which may help
make future decisions to improve the environmental quality of the
lake.
The alternative actions called for are as follows:
1. Adding treated effluent from the City's sewage treatment plant.
2. Raising the lake level by building a weir at the Madonna Road
culvert.
3. Dredge the central area of the lake and deposit the spoils at a
selected location in Laguna Lake park.
The 1981 Lake Management Program envisioned that the Prefumo arm would
act as a siltation basin to collect most sediment before it reached the
lake. This inlet would be cleaned every few years as needed to
preserve its function, which is the course followed by the City. Some
material would still find its way to the main body of the lake,
creating the need for silt removal at infrequent intervals. The time
has come for this more major program.
����n���i► I'I!Ilip1d ip�,jl city of San Luis OBispo
WNGs COUNCIL AGENDA REPORT
Laguna Lake
Page Two
Implementation Program
Following City adoption of the program, staff took the following
action:
1. Purchase and use of mechanical weed harvester. The weed harvester
was purchased and operated by the City for several years, and the
weed problem was dramatically improved to the point that it has not
been necessary to use the harvester in recent years. The harvester
is still owned by the City and is located at the Corporation Yard.
2 . Removal of sediment from the Prefumo inlet. The arm was cleared of
15,000-20, 000 cubic yards of material in 1977; 13,800 cubic yards of
material in 1983; 4,000 cubic yards of material in 1986; and
6, 600 cubic yards of material in 1990.
In removing this material staff has carefully followed the
directions of the Fish and Game, the Corps of Engineers,
environmental requirements, both as directed by the 1981 EIR
(Exhibit B) , and as determined by the Community Development
Department staff. Note in particular that the 1981 environmental
determination called for willow thickets at the banks of the channel
to be maintained to prevent soil erosion. In addition, willow
thickets in the last few hundred feet of the channel were also to be
maintained in order to provide better sediment retention.
3 . Temporary dam at Madonna Road culvert. Every spring the City
installs boards at the outlet of the culvert under Madonna Road.
This must be done after heavy rains are over so as not to limit the
capacity of the culvert if a big storm should occur, but prior to
the- last rain of the season so as to capture as much spring runoff
as possible. This allows the lake to begin the summer at a higher
level, thus providing some mitigation for evaporation which occurs
during the summer months. Placement of the boards does no good,
however, if the lake does not spill, which has been the case for the
past couple of years.
4. Monitorinq_nrogram. For a six months period in 1979 and 1980, the
City conducted an extensive monitoring program, measuring eight
different characteristics at various water depth over the entire
lake. This was done in anticipation of a State requirement which
called for treated sewer effluent to be discharged to Laguna Lake.
That State requirement and associated funding were later withdrawn.
Although the lake has since dried up, staff believes the basic
characteristics of the lake (such as temperature, turbidity, oxygen
and chemical constituents) will be substantially the same when rains
once again fill the lake to its former level.
l!Ii; city of San lues osIspo
COUNCIL AGENDA REPORT
Laguna Lake.
Page Three
Alternative Actions
1. Adding treated effluent from the City sewage treatment plant. In
1977 preliminary studies were conducted indicating that this was a
feasible project, assuming tertiary treatment of the City's sewage.
In the early 1980's the State requirements and funding were
withdrawn when EPA determined that it would not fund tertiary
treatment, which is a higher level than required by the Federal
government. The local Water Quality Control Board, however, has i
insisted on tertiary treatment, the design of which is now going
forward. The primary concern about discharging to Laguna Lake has
to do with the increase in nutrient loading to the lake. Additional
processes are needed for nutrient removal, thus allowing discharge
to the lake. Utilities Department is recruiting a Wastewater
Reclamation Coordinator who will evaluate alternative reclamation
projects. Use of reclaimed water to augment Laguna Lake will most
likely be one of many options evaluated.
2. Raising the lake level by building a weir upstream of the Madonna
Road culvert. This project would involve construction of what would
appear to be a dam upstream of the Madonna Road culvert, thus
keeping the lake at a higher level without the mechanical action of
placing boards in the culvert. The dam would be located far enough
upstream that the culvert under Madonna Road would act at full
capacity during the floods. This project is currently estimated to
cost roughly $350,000. Negative aspects were that water would be
deeper through the lake for longer periods than the temporary board
installation conducted by the City, thus some wildlife habitat would
be flooded and some private improvements along the lake would have
to be modified. There is also a problem with sediment buildup
behind the dam and a possible problem with erosion due to wave
action on the larger lake. Staff has not pursued this alternative,
since it is relatively expensive and much of the same effect can be
achieved by hand placing boards in the outlet structure every
spring.
3. Dredging of Laguna Lake. This alternative includes several sub-
alternatives, which are the primary subject of this agenda report.
Each of these alternatives will be discussed in some detail.
Dredging Alternatives:
a) Removal of delta at outlet of Prefumo Arm (Exhibit C-a)
This alternative represents a continuation of the sediment removal
projects the City has periodically conducted in the Prefumo Arm.
/-.3
city of San Luis o81Spo
COUNCIL AGENDA REPORT
Laguna Lake
Page Four
The project would remove as much material as is practical using
earthmoving equipment. This can only be conducted when the lake is
very low, thus it might not be practical if there are sufficient
rains to fill the lake this winter. Material would be trucked off-
site, possibly to a nearby ranch. Maximum material which might be
removed by this method 25,000 cubic yards. Cost $130,000.
b) Lowering of bottom of main portion of lake by an average of 5 feet j
(Exhibit C-b1
This earth removal might be accomplished by suction dredge, or
possibly by standard earthmoving equipment (if the lake level is low i
and the water table can be additionally lowered with well tips) .
Material removed would be deposited on approximately 25 acres of
City owned property northwest of the developed portion of Laguna
Lake Park (Exhibit D) . Material to be removed 500,000 cubic yards.
Cost $2,700,000.
c) Lower of bottom of all water area of lake to elevation 106 or an
average of 5 feet (Exhibit C-c) .
This is a larger version of b) and is the one recommended in the
Lake Management Plan. Material to be removed 700,000 cubic yards.
Cost $3,700, 000.
d) Lower Prefumo Inlet and remove all trees so as to recreate the lake
arm condition envisioned with the original development
(Exhibit C-d) .
This alternative might be done in conjunction with Alternate b) or
c) . Material would be hauled away. There might well be problems
with Fish and Game, the Corps of Engineers or environmental concerns
with this alternative. Material to be removed 50,000 cubic yards.
Cost $280, 0008 if a dry working condition can be achieved. If wet
conditions must be dealt with, costs might triple, together with
substantial mess in trying to haul wet material from the site.
There are a number of intermediate alternatives which could be
considered; that is, different depth of earth removal and different
areas. As a general rule it will cost approximately $500,000 for each
foot of lake dredging. The figures shown are contract estimates. It
might be possible for the City to purchase a dredge, hire several
employees and conduct dredging, drying and earth spreading operations
for a number of years.
f-JAI
i�ll!'I city of San tuts OBISpo
COUNCIL AGENDA REPORT
Laguna Lake
Page Five
General Discussion
The dredging alternatives imply pumping of the slurry to a series of
holding ponds on undeveloped park property (Exhibit D) , from which
water could filter back to the lake and evaporate, leaving the silt to
dry. Controlling flow to these ponds, managing them and eventually
spreading the dried material on the park property will require a major
effort and expense. The level of the park in this area could be raised
as much as 10 feet upon completion of the project.
Permits
Any of the alternatives are subject to review and permit approval by
the following agencies:
California Fish and Game, State Water Resources Control Board,
Federal Fish and Wildlife and the U.S. Corps of Engineers. Fish and
Game and Fish and Wildlife are looking to protect fish life, bird
life and other wildlife. The Water Resources Board is looking to
see that waters are not polluted, and the Corps of Engineers is
looking to preserve wetlands. Any City project which conflicts with
these primary interests might be denied or severely restricted. It
currently takes 6-8 months to process a permit application for even
a simple project with the Corps of Engineers. Permits will not even I
be considered until a project is in a final stage of design.
Approval conditions may be costly or onerous and the permit might be
denied.
Environmental Determination
Most of the alternatives were discussed in the 1981 EIR, however a
recent rather extensive study by the Community Development Department
has determined that alternatives b, c, and d will require a focused
EIR. This may cost $70,000 and will probably require at least a year.
The EIR will have to be largely completed prior to start of detailed
design.
FISCAL IMPACTS
All cost figures are based on very preliminary information, however,
they should be in order of magnitude and relative to each other for the
various alternatives.
Zone 9 makes available funds for minor creek contract maintenance
projects such as periodic silt removal. A request has been made of
Zone 9 for $50, 000 for silt removal at the delta.
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i°ilill�,14lll!Ili1°"1iijl�Ifli city of San LUIS OBISpo
�' COUNCIL AGENDA REPORT
Laguna Lake
Page Six
Staff is aware that there have been grants available from various State
and Federal agencies for lake restoration. These include the EPA Clean
Lake Program, a Department of Agriculture Clean Water Program, a State
Department of Parks and Recreation "Land and Water Conservation Fund",
a State Urban Open Space and Recreation Program, and Wildlife
Conservation Board Bond Act funds. Staff has not investigated these
sources of funds, however use of grant funds is always subject to
detailed submittals, requiring significant time as the City competes
with other communities for the limited funds. Grant programs, if the
City is successful, often take a number of years to process and
administer. Funds available within grant programs have been greatly
reduced within recent years.
Lake dredging could also be funded by an assessment district.
Assessment districts are costly and cumbersome with several public
hearings required. A primary decision to be made would be: "Who
benefits and by how much by the dredging of the lake?" The abutting
property owners benefit more than those living further away. Park
users will benefit; how can they be assessed?
Lake dredging could be funded from the General Fund. No funds are
budgeted at this time for additional dredging at Laguna Lake. Because
of current pressures on the fund, major lake projects would have to be
phased over several years.
STAFF RECOMMENDATION
Staff feels that removal of material from the delta (Alternative a) is
of primary importance and is a continuation and an extension of the
existing maintenance program. Staff is currently preparing plans and
has submitted a funding request to Zone 9. City will need supplemental
funds of approximately $80,000.
Staff does not recommend re-creation of the inlet condition envisioned
by the original developer (Alternative d) . This would involve removal
of many trees along the inlet banks, contrary to the Management Plan,
the EIR, and the wishes of Fish and Game, and the Corps of Engineers.
Staff also anticipates some opposition from the neighborhood. Most
important however would be the virtual impossibility of retaining water
depth in this inlet without development of expensive silt retention
facilities upstream of the city in Prefumo Canyon. Acquisition and
development of this facility would be quite complicated and time
consuming.
Dredging of material from the main body of Laguna Lake must be done
some time or the lake will eventually become a marsh, then eventually a
meadow. The primary question facing the Council is whether now is the
appropriate time to move ahead with the program.
MEETING DATE:
city of San LUIS OBispo
COUNCIL AGENDA REPORT REM NUMBER:
Laguna Lake
Page Seven
Staff believes that the long range viability of the lake must be
addressed soon. Because of the difficulty in financing such major
costs as are implied by dredging, staff does not feel this program can
or should be funded solely from the General Fund. It is possible that
all sources, i.e. user fees, assessment district, grant and general
funds, will be needed. This would be an appropriate topic of
discussion for the Laguna Lake Park Committee to review.
Council should indicate whether it favors dredging only the main body
of the lake (Alternative b) or dredging the entire water area of the
lake (Alternative c) .
Attachments: Exhibits a-d
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I I. SUMMARY
A. PROJECT DESCRIPTION
The proposed Laguna Lake Management Program consists of three phases
that would result in the following City actions:
1. Purchase of a mechanical weed harvester for clearing appropriate
portions of the lake.
2. Periodically remove accumulated sediment from the Prefumo inlet and
delta.
3. Construct a temporary log dam approximately one foot in height at
the downstream end of the Madonna Road culvert.
4. Establish a monitoring program to document the effects of the actions
listed above and also provide additional data which may help make
future decisions to improve the environmental quality of the lake.
In addition, three principal alternative actions, considered as part of the
Management Program, would be pursued by the City. These "future
alternatives" are as follows.
1. Adding treated effluent from the City's sewage treatment plant.
2. Raising the lake level by building a weir at the Madonna Road cul-
vert.
3. Dredge the central area of the lake and deposit the spoils at a
selected location in Laguna Lake park.
B. ENVIRONMENTAL IMPACTS AND MITIGATION
Environmental impacts that would result from project implementation and
available mitigation measures are summarized as follows:
1. Water Quality
a. Proposed Actions
Weed Harvester
This would prevent the buildup of rotting material and unwanted nutrients
in the lake. No adverse impacts on water quality are expected.
�-9
L :,.*'pSEFUMD INLET
The primary importance of the Prefumo Inlet is in its capacity as a major storm
runoff channel and a sediment catchment basin. Other uses listed below are
secondary and of much lower importance.
Appropriate Uses
Sediment Retention
Flood Control
Riparian Wildlife Habitat
Education
Passive Recreation
Physical Condition and Management Requirements
Sediment Retention and Flood Control : The inlet channel should be developed
and maintained so as to adequately carry flood waters and capture sediment
material before it reaches the lake. Sediment must be removed on a periodic
basis and the channel bottom maintained at an elevation of 116 to 117 feet MSL.
Convenient access into the channel for heavy excavating machinery will be
:: .required. Sites for disposal of excavation material will have to be located on
jtF an as-needed basis.
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'willow thickets at the banks of the channel should be maintained to preve7here
;j.:bank erosion. Willow thickets within the channel bottom should be remove
except in the last few hundred feet of the channel mouth. Willow thicket
Will help to slow water velocity i•n the upper reach of the inlet and thus aid
ik_1n the sediment retention function. However, if the entire inlet is returned
:r to its original design, all willow thickets on the bottom must be removed.
";.'Wildlife, Education and Recreation: Sediment retention and removal must be
conducted so as to minimize impacts to wildlife. Excavation should be done
such that a channel for trout migration is maintained. Willow thickets,
especially at the northern end of the inlet and along the inlet banks should be
retai ned.
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SAN LUIS OBISPO, CA
MEETING AGENDA
DATE ITEM#
Bear City Council:
Rs owners of property adjacent to the Prefumo Inlet we are very
supportiue of re-creating the lake arm. Reestablishing the lake in this
area will increase the habit value, reduce the fire hazard, increase
safety, and ensure the long-term viability of Laguna
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Thank you for your consideration in this matter. O*cvc-mmd Q CDD DUL
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RECEIVED
�! ea FEB 19 1991
SAN LUIS OBISPO. CA
Dear City Council:
Rs owners of property adjacent to the Prefumo Inlet we are very
supportive of re-creating the lake arm. Reestablishing the lake in this
area will increase the habit value, reduce the fire hazard, increase
safety, and ensure the long-term viability of Laguna Lake.
Thank you for your consideration in this matter.
Name Rddress
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Dear City Council:
Rs owners of property adjacent to the Prefumo Inlet we are uery
supportiue of re-creating the lake arm. Reestablishing the lake in this
area will increase the habit ualue, reduce the fire hazard, increase
safety, and ensure the long-term viability of Laguna Lake.
Thank you for your consideration in this matter.
Name Rddress
vjzu
SLD CA 3y a
nit
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Erg 1 1991
OITY COUNCIL
sAN LUIS OBISPO.C6