The URL can be used to link to this page

Home My WebLink About02/05/1991, 7 - LAGUNA LAKE MANAGEMENT I��III��I��III MEETING DATE: �I�� ink► C1 o San tuITEM N ts OBISp0 U y R: 1991 COUNCIL AGENDA REPORT TEM NUMBER: FROM: Dave Romero, Public Works Director ��XlC 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. 7/ ��►►i�Villllll��luP1u�gl�lll city of San Luis OBIspo 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 . Monitoring program. 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. y i ! -A ��i,,�►bhilililllillll11° ��il city of San tuts OBISpo V6% COUNCIL AGENDA REPORT Laguna Lake Page Three I 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 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 j 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: i 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. 7- Il�l�i�►►�fu►Illilll{I1° �IIIIIU city of San Luis OBISpo 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 (Exhibit C-b) This earth removal might be accomplished by suction dredge, or possibly by standard earthmoving equipment (if the lake level is low 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. I 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. I d) Lower Prefumo Inlet and remove all trees so as to recreate the lake arm condition envisioned with the original development (Exhibit C-d) . i 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 $280,000, 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. I ��IdiIIiIIIIII�� IIIIIII city of San tuts OBISpo IiiN 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. t Permits Any of the alternatives are subject to review and permit approval by the following agencies: i 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 j 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 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. I 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 i 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. 7-S ��iii�iin►►►�►IIIIIIIIP1°"°'��IU city of San Luis OBlspo COUNCIL AGENDA REPORT Laguna Lake Page Six Staff is aware that there have been grants available from various State i 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. I 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: ��►�►III�IIIIIIII�° llUlll city of san tuts OBISpo ITEM NUMBER: COUNCIL AGENDA REPORT 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 I I lglkmgmt/dfr#26 77 'I Lu 1d e� IM ta CM pm T ep Qf e0 _ ■=zz LUI=O 20 100 0.1 LLJ Cm Cc 10 � o 14� 4Jcu itis c '� ItsS Wcu � N Of N T ' / C J N v OJ 4r— WI=0 of i I 14 1 LU' » ' '• ,_;,-� 111 ,J( .i•� ;,'l moi/ H�c c� ; Wim +, 4-3 m 4j to el - / zlvr .I �. / �, - it j• l I. SUMMARY A. PROJECT DESCRIPTION The proposed Laguna Lake Management Program consists of three phases that would result in the following City actions: f41. 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. . 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. I 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. i 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 I . This would prevent the buildup of rotting material and unwanted nutrients in the lake. No adverse impacts on water quality are expected. � 9 1 � x�, � Io,f •�I - z � �. RE UMO INLET N'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 .7.'.-secondary and of much lower importance. Appropriate Uses Sediment Retention Flood Control Riparian Wildlife Habitat Education Passive Recreation Physical Condition and Management Requirements ediment 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 n as-needed basis. illow thickets at the banks of the channel should be maintained to prevent bank erosion. Willow thickets within the channel bottom should be removed prevent except in the last few hundred feet of the channel mouth. Willow thickets here d Mill help to slow water velocity i-n the upper reach of the inlet and thus aid n the sediment retention function. However, if the entire inlet is returned to its original design, all willow thickets on the bottom must be removed. ildlife, Education and Recreation: Sediment retention and removal must be conducted so as to minimize impacts to wildlife. Excavation should be done Uch 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 etained. 37 ( W YZI 10 Go cc , i. ' z figure 12 ,, 81 E )4 zfa i f C d _ Xm CW AlK ZA X/lLU to co cc i or Cw � r V , CO �J figure 811 R UP , I'l/ Y/� qy • r / I z fj'a-8 L' �,\ < f12 igure a' - - �; b t C • �� X . l� ... .. , //� �/ �/ '•, � / //!�/�`. pry., i •``\ \_ .T. _ h ' �',i,i/ J � � �l,��.��/ // '� ; Y ^1 %� � _ �/'may -• ,ISE ;ice��a ��'; � •�� `; .s�l�'�� - ��7? `` � i V W 61, CO ca / ✓ t7 TQ�ljj � CO L=/fr' cv - V etJ figure 1 w ex_ _ - ��.,/;�/ lig• _ i_ / ��Q//%/,�/ //`:' `•.V\�`!\ "�P, ".,�` '\ �\ 17\yam 2 ;•, =ter. � 2 , Lm POP/ Lm \ 1Q � i l J n 9 � x bg co n I 2 o m figure 9 70 EX ��13 _s- % 4 February 1991 W To: The ynora HQle Mayor and City Council Froms Dorothea Sible 1215 Mariner' s Cove San Luis Obispo, CA 93405 --- ' 543-6105 It is with considerable relief of my long standing concerns that you have at last under consideration some mitigating measures in regard to the deplorable deterioration of one of this city's greater assets --Laguna Lake. Having lived on and been a keen observer of the lake, It's function, uses and ecology for the past 25 years I feel qualified to address this subject. In consideration of your schedules, and my own, only a few points will be addressed herein. I urge you to authoriz* implementation of Alternative a, Exhibit C-a, Item 7-Agenda of 2/5/91. Staff is well aware , and I have maps and pictures illustrating, this area was:•open lake, essential to inlet drainage. No silt removal has ever been conducted in this area. One clearing of willows and brush was executed by CMC crews. I have personally spent many hours and over $29000. on removal of dead fallen willows, etc, from city property which have impinged upon my property. The time frame is of considerable importance. Nine months delay puts the project in the next normal rainy season. Most of this delta has been above standing water for many months (years. ) No fish, frogs, crayfish, bittern, green and blue heron remain. The dense covering of willows, reeds, rushes, sedges, grasses and and coyote bush present the next logical site for a voldtile fire such as has occured onthe park side of the lake. In this instance there are homes in line of the prevailing wind. This is a constant concern as many people frequent this delta area. I feel compelled to urge immediate clearance of this heavy vegita- tion. I also feel compelled to have my insurance carrier document the hazard. Sincerely, J RECEIVE ® FEB S MCI CITY eLEFK SAN LUIS OBISPO,CA MEER AGM DATE 7---V ME 1210 Oceanaire Dr.. San Luis Obispo, CA 93405 Phone: (805) 541-2319 February 4, 1991 To: The San Luis Obispo City Council Subject: Removal of Silt from the Laguna Lake Basin 1 urge the City Council to take whatever steps are necessary to remove the accumulated silt from the Laguna Lake basin and associated inlets. The lake bed is currently so shallow that it can hold only a small amount of water. This makes its effective area very dependent on the rain- fall, so much so that our current drought has resulted in much of it having dried up; only the ducks find the island in the middle attractivel Making the lake basin deeper would make it more effective as a reservoir since its effective area would then not drop so rapidly during periods of drought such as we are now experiencing. It would then be enjoyable to visitors to the park more of the time and would serve the needs of wildlife in the area more effectively. Since our house on Oceanaire backs up on the Prefuma Inlet to the lake it would be to our advantage if the inlet was sufficiently deep to make it a permanent part of the lake. However, the general community would benefit too; in wetter years the shallow inlet by Los Osos Valley Road has been foul ... a perfect breeding grounds for mosquitoes. Hopefully the recent dredging has reduced the chances of this happening again, but making it a permanent part of the lake would take care of the problem forever. It would also increase the possibilities for those who go boating on the lake. I hope the Council will consider that the restoration of the lake and its surrounding areas is a feasible and desirable undertaking for San Luis Obispo. Sidney Bertram, Ph.D., Retired Electronics Engineer COP�aT'O: Do O'CMDR 1 P� ❑ PQV.MX �o RECEIVED M�oma O Poucec FL oMC MT.TEAM ° OWN& FEB 5 1991 CJMADEILE CITY COUNCIL LUIS OBISPO,CA