This report describes Southern California Edisons’s (SCE’s) Limnology Study Plan for Lake Isabella. It includes the study objectives and proposed methods for obtaining and reporting the study results.

The Limnology Study Plan for Lake Isabella has two major objectives:

• Determine if Lake Isabella stratifies during the summer months and if its thermal structure affords opportunities to manage reservoir releases to control water temperature conditions in the Kern River below the reservoir. The water temperature conditions largely determine the type of fisheries that the river will support.
• Determine whether reactivating water diversions at the historic Borel intake would adversely affect the limnology (water quality and aquatic biological resources) of Lake Isabella. SCE generally reactivates the old intake when the reservoir water level is too low to divert water at the Auxiliary Dam (elevation below 2,548 feet msl).

The Department of Fish and Game (CDFG) requested that SCE collect data on water temperature profiles in Lake Isabella once a month from June through September to evaluate potential effects of varying lake storage releases on the temperature regime of the Kern River. A water temperature study conducted in 1987 (SCE 1988) showed that the water temperatures in the lower Kern River are strongly affected by temperatures of the water released from Lake Isabella at the Main Dam and the Auxiliary Dam. The Main Dam releases water directly to the Kern River and the Auxiliary Dam releases water to the Borel Canal. The canal conveys water to the Borel Powerhouse, which releases to the Kern River about 7 miles below the reservoir. The CDFG requested that SCE determine the temperature profiles at deep-water locations in the reservoir near the Main Dam and near the Auxiliary Dam. The Sequoia National Forest (SQF) asked that dissolved oxygen (DO) profiles also be determined. The State Water Resources Control Board recommended including May sampling in the study

The SQF and Ron Hyatt, owner of Sierra Sailing, submitted study requests to evaluate effects of diverting water at the old intake on the North Fork of the Kern River. Normally, the Borel Project diverts water at the Auxiliary Dam, but during very low water years water cannot be diverted at the dam and the Project may divert water at the old intake. Because water that is diverted at the Auxiliary Dam has passed through Lake Isabella, it provides some water exchange and circulation in the reservoir. However, water that is diverted at the old intake, which is upstream of the reservoir, bypasses the reservoir. The resulting reduction in water exchange and circulation may exacerbate poor water quality conditions caused by the low lake levels. These conditions would likely include increased water temperatures and reduced concentrations of dissolved oxygen.

The SQF, in their comments on the First Stage Consultation Package, provided the outline of a limnological study plan to investigate the effects of diverting at the old intake. The SQF plan recommended one sampling period before and two sampling periods after reactivating the old intake. The "before" sampling period would be during summer shortly before initiating the diversions, while one of the "after" sampling periods would be during summer and the other "after" period would be during late fall or winter. The SQF plan recommends measuring water temperature and DO profiles, collecting water samples for six water quality parameters, and obtaining plankton tows. The plan states that the study area should include the reservoir near the Main Dam, the Auxiliary Dam and in the North Fork arm.

The principal objectives of the limnology study for Lake Isabella are those presented in the introduction. In addition, the study will document a range of water quality conditions in the reservoir. The study will determine water temperatures and DO concentrations that occur in the main body of Lake Isabella during May through September, generally the warmest months of the year. This information will be used to determine habitat suitability for fish in the deep, open water portion of the lake during the summer and, as noted in the introduction, will be used to evaluate the potential for managing water temperatures in the Kern River below the dam.

The study will also compare water quality conditions and zooplankton populations in the reservoir when the Borel Project is diverting water at the Auxiliary Dam (downstream of the reservoir) and when the Project is diverting water at the old intake (upstream of the reservoir). The comparisons will focus on biologically important water quality parameters, such as water temperature and dissolved oxygen levels, that are specifically addressed in the SWRCB’s Water Quality Control Plan for the Tulare Lake Basin (Basin Plan).

This section describes methods for sampling designed to determine the water quality profiles and thermal stratification of the reservoir.

Water temperature and DO profiles will be obtained once a month from May through September, during the third week of the month. Temperature and DO will be recorded at one-foot depth intervals over the first ten feet from the surface and at 2.5-foot intervals for greater depths. A water-quality meter (Hydrolab DataSonde 4) with a 100-foot probe will be used for the temperature and DO measurements. Specific conductance and pH readings will also be recorded. The meter will be calibrated before each day of sampling and calibrations will be checked at the end of the day.

The water quality profiles will be collected at approximately the same locations that were sampled in October 1987 for SCE’s water temperature study (Flow Science Inc. 1988). One of the stations of the 1987 survey was near the Main Dam and the other was near the Auxiliary Dam. The stations will be set at least 500 meters upstream from the dams to avoid any effects of turbulence from water flowing out of the dam outlets. A global positioning system (GPS) will be used to fix the stations locations. The secchi depth will be recorded and meteorological conditions will be noted at each station.

This section describes methods for sampling designed to evaluate effects on reservoir limnology of diverting at the old intake.

Sampling will be conducted during three times of year: once during the summer shortly before reactivating the old intake, once during the summer about a month after initiating diversions, and once during cool weather while diverting at the intake. Three stations will be sampled during each of the sampling visits. Two of the stations, near the Main Dam and the Auxiliary Dam, are the same as those described above. The third station will be in the North Fork arm of the reservoir, about a mile downstream of the old intake.

Water quality profiles (temperature, DO, pH and specific conductance), water samples for water quality analyses, and plankton tows will be obtained at each sampling station. The water quality profiles will be collected as described in the previous section. The water samples will be collected with a horizontal water bottle from the following three depths: three feet below the surface, three feet above the bottom, and midway between the surface and bottom. However, if the reservoir is thermally stratified, the third sample will instead be collected from the middle of the thermocline. The water samples will be decanted into appropriate containers, placed on ice, and transported to a certified laboratory for analysis of alkalinity, hardness, total dissolved solids, total nitrates and total phosphorous. Appropriate chain of custody protocols will be followed. The secchi depth will be recorded and meteorological conditions will be noted at each station.

Two replicate zooplankton samples will be collected from each station. The samples will be collected with a Wisconsin plankton net towed vertically from near the bottom to the surface. The net has a 5-inch diameter mouth opening and 63-µM mesh netting. The zooplankton samples will be preserved with Lugol’s solution for later enumeration using a dissecting microscope.

A draft technical report of the results will be prepared following completion of the field season. The report will provide graphs showing the water temperature, DO, pH and specific conductance profiles for each station and sampling date and will include tables with the results of the water quality analyses. Water quality results will be compared with the Basin Plan objectives. Tables and graphs with estimates of zooplankton abundances for each station and depth will also be provided. The report will include a discussion of the potential significance of the results for fish and other biological aquatic resources in Lake Isabella and the Kern River.

Most of the fieldwork will be performed during May through September 2001. A final sampling to evaluate effects of diverting at the old intake will be conducted in November or December. The results will be presented at a technical meeting during the first or second quarter of 2002.

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