ECOLOGICAL RESEARCH ASSOCIATES REPORT ON SYNOPTIC SURVEY  OF LAKE WILDWOOD ON 19 MAY AND AUGUST 5, 2005

DR A F T

Introduction  

The purpose of this report is to present management recommendations for the Lake Wildwood Association (Association) aquatic vegetation control, and Lake drawdown and potential sediment removal operations. Water quality parameters from recent synoptic monitoring (ERA, May 19, 2005), routine sampling by Lake Wildwood Association Public Works Department personnel, and other ancillary data are utilized in this analysis. Concerns from Friends of Deer Creek (May, 2005) are addressed either specifically or within the context of the management recommendations.

 Lake Wildwood was constructed in the late 1960’s, and Lake Wildwood dam was closed and the lake first filled in December of 1969. The Lake’s watershed of 54.5 square miles includes Scotts Flat and Deer Creek Reservoirs, which receive water from a greater area than Lake Wildwood’s receiving watershed (Figure 1). The Lake covers approximately 260 acres, with a volume of 4,818 acre feet and a depth of approximately 53 feet from an original maximum of 58.5 feet. Lake Wildwood purchases 200 miners inches of water per year (approx 6.4 mgd) from the Nevada Irrigation District (NID), half of which flows through the Lake to customers downstream. The average annual flow through Lake Wildwood is estimated to be approximately 94,957 acre-feet (Workplan, 2001).

 Sediment deposition to the Lake is high, with approximately 37,000 cubic yards deposited annually. This relatively high deposition is in part due to past gold mining activity which has modified the watershed. This sediment trapping by the Lake has caused the stretch of Deer Creek between the spillway to the confluence of Squirrel Creek to be sediment starved.

Deer Creek baseline flows during the summer are typically not more than 3 cfs as measured by the Nevada Irrigation District (NID) upstream of the WWTP effluent discharge site during the summer months. Year-round flow rates are not normally available at this site. Deer Creek flows are measured at the USGS Smartville gauge at Moody Flat Road, which capture inflow from Squirrel Creek and other feeder streams, as well as the Lake Wildwood WWTP effluent (Figure 1). Based on data from this site, the probability of a natural 280 cfs flow (approximately the peak discharge amount from the fall drawdown operation) is estimated at 15 percent in the month of October. Squirrel Creek dominates the flow of lower Deer Creek to the confluence of the Yuba River during most of the year (Workplan, 2001).

Figure 1. Lake Wildwood Watershed and Study Area.

Fall Drawdown Operations

  The Association undertakes an annual fall drawdown of the Lake in mid-October during which The Lake is lowered 10 feet, in order to remove accumulated sediment from the previous year and to perform maintenance on piers and other infrastructure. The process takes approximately 7 days, which varies slightly from year to year based on changes in ramp-up curves to address turbidity and temperature concerns, explained in more detail below.

  The fall drawdown operation is regulated under the NPDES (National Pollutant Discharge Elimination System) No. CAG995001, Waste Discharge Requirements General Order No. 5-00-175. This “low water quality threat” general permit covers discharges that “do not contain significant quantities of pollutants” and “are either (1) four months or less in duration, or (2) the average dry weather discharge does not exceed 0.25 mgd”.  This permit expired on June 1, 2005 and must be renewed.

  A Notice of Violation (NOV) from the Central Valley Regional Water Quality Control Board was sent to the Association on November 20, 2000 regarding exceedance of settleable solids, turbidity (NTU), and temperature. Another notice on February 14, 2002 was sent, regarding the exceedance of standards for turbidity and dissolved O₂. Differences in data values from sample collected by DFG and those collected by the Association are shown, and we suggest that these are largely due to differences in sample location and timing. Indications are that most sediment originated from the erosive force of surge water which scoured the banks of Deer Creek of accumulated silt, algae, and debris from the previous years wet season. The Workplan for Lake Wildwood Fall Drawdown (Workplan, 2001), formulated in response to the first NOV, presented a set of recommendations. These included improved pre- and post-drawdown monitoring and sampling methodology to establish more complete ambient baseline and drawdown conditions, and refinement in valve opening and discharge blending from different depths to reduce turbidity and temperature. These were further refined in response to the 2002 NOV and implemented during the fall drawdown in 2003 (Lake Wildwood, 2003), when results showed that turbidity was not significant in Deer Creek during the entire drawdown except for the initial flushing of the discharge system.

  The fall drawdown in 2004 further suggests that a gradual drawdown of the Lake via partial opening of the discharge valve over one week results in lower temperature fluctuations and turbidity ( Lake Wildwood, 2004). The Lake discharge of cooler deeper water initially changed the daily water temperature fluctuations of 14 – 17 C ° at the beginning of the drawdown to  a constant 14 C ° at the time. As drawdown of warmer overlaying water continued during peak drawdown the temperature reached 16 C °. Dissolved O2 remained at 8 mg/l or higher throughout the discharge. Turbidity levels exhibited the same characteristics of initial elevated levels due to accumulated debris from the previous season and algal growth on the outlet structures. However, levels were at or below the ranges found in Deer Creek during the wet season.

Synoptic Survey of May 19

On May 19, 2005, Dr. Charles Goldman, Ted Daum, Rene Henery, and Ali Ger of Ecological Research Associates (ERA), Davis, California conducted a water quality survey on Lake Wildwood. Sample sites are shown on the site map (Figure 2). Samples were taken throughout the lake despite almost continual rain and peak inflow from the two major tributaries. The hydrograph (Figure 3) indicates the inflow exceeded 2500 cfs.

Water samples were taken using two Lake Wildwood Association Public Works Department Vessels. Composite water samples were taken from depths of 1 meter and 1 foot above the bottom and analyzed for total phosphate, total dissolved phosphate, and soluble reactive phosphate.

An Eckman sediment sampler was used at selected locations to provide an indication of hydrogen sulfide production from reduced conditions and the extent o internal nutrient during stratified conditions. A YSI sensor was used at selected sites for vertical profiles of temperature, conductivity, and dissolved O² (Figure 2). A bathymetric survey was run on 7 transects using a depth finder (Figure 4).

Figure 2. Lake Wildwood Sampling Sites and Landmarks for ERA sampling on May 19, 2005 and Lake Wildwood Association sampling from May 27 through August 4, 2005.

The survey occurred during an unseasonably heavy late season storm. The flow over the dam was high, as shown on the USGS Deer Creek Smartville gauge hydrograph in Figure 3 with readings from before, during, and after the survey.

Figure 3. Deer Creek Flow and Discharge, May 18 through May 23, encompassing the storm that occurring during the May 19 sampling.

Figure 4. Lake Wildwood Bathymetry Survey, May 19, 2005.

Profiles from near the standpipe (Site 1a) show a dissolved O₂ isocline at 10 feet, similar to the depth found at sites 3 and 4, the other deep water sampling sites at mid-lake (see Figure 2). These low oxygen conditions indicate the high potential for nutrient loading as reduced bottom sediments move from oxidized to reduced states, releasing phosphorus and iron to the overlying water. Temperature also decreased to approximately 10° C at these sites. The profiles indicate more mixing at the shallower sites (8 – 10 ft), particularly at the high-energy inflow sites for Wildwood Creek (Site 2b), and Deer Creek (Site 7). Depth profiles from the 7 transects are shown on Figure 5. 

Oxygen temperatures and conductivity profiles were taken throughout the lake (Figure 5). Despite the heavy inflow weak thermal stratification had begun to develop prior to the storm. At the outflow (Sites 1a and 1b) and midlake stations (Sites 3 and 4) oxygen levels were at zero. As previously noted these conditions provide internal nutrient loading from the phosphorus rich sediments that accumulate on the lake bottom. At both Deer Creek and Wildwood Creek tributary mouths the inflow waters, although phosphorus rich, were well mixed and had high oxygen content.

High conductivity reflected the heavy sediment transport from the upstream watershed. At Site 6 evidence of oxygen loss was evident at 8 feet of depth, but conductivity appeared to be lower. Further towards the stream mouth (Site 7), well mixed conditions existed with uniformly lower conductivity in the well mixed inflowing water (from the rainstorm that was in progress).

Further towards the stream mouth (Site 7), well mixed conditions existed with uniformly lower conductivity in the well mixed inflowing water (from the rainstorm that was in progress).

Figure 5. Oxygen, Temperature, and Conductivity Profile Data from ERA Site Visit, May 19, 2005.

Water chemistry for total phosphate (TP), soluble reactive phosphate (SRP), and total dissolved phosphate (TDS) samples were strongly influenced by the inflowing tributaries (Figure 6). Sampling was done during a peak inflow period with heavy sediment content in the tributaries. Since sediments adsorb phosphate it is not surprising that TP levels were very high at Site 2b (Wildwood Creek inflow site) and Sites 6 and 7 which were Deer Creek inflows. The higher SRP noted at Site 4 may indicate some additional fertilization from greenbelt areas at Vista Point and/or Black Bart Bench greenbelt. Since Deer Creek draws an extensive watershed which includes Nevada City and its wastewater treatment plant, it is not surprising that phosphate levels of the inflowing waters are high. As water moves through the system from the major tributaries to the outflow, it is not surprising that total phosphorus was greatly reduced through sedimentation and nutrient uptake by phytoplankton and higher aquatic plants.

Figure 6. Phosphorus Values for ERA May 19, 2005 Sampling.

Once the lake is in more stable summer conditions, it would be useful to do a second synoptic in order to compare nitrogen and phosphorus levels throughout the lake to pinpoint areas of excessive nutrient loading. We have every reason to expect surface discharge from the lake during winter inflows to be of higher quality than water entering the system. Both sedimentation and nutrient stripping by phytoplankton and higher aquatic plants takes place in Lake Wildwood.   

Lake Wildwood Association Water Quality Sampling

  Results for Lake Wildwood Association routine water quality sampling which took place between May 27 and August 4, 2005 are summarized in Appendices 1 and 2. E coli levels exceeded Basin Plan guidelines in the June 23 sampling at Meadow Park Bridge, and in the June 30 sampling at Deer Creek, Lake Wildwood Creek, and Meadow Park Bridge. This dataset was started eight days after our synoptic and included surface water coliform and E coli bacteria, conductivity, and temperature with several transparency measures.

  In general, E coli levels fell below the 200 mpn/100 ml Basin Plan Water Quality Objective but exceeded this level at Meadow Park Bridge on June 23, June 30, July 14, July 21, and
August 4, 2005. Wildwood and Deer Creeks also exceed the 200 mpn level on June 30. This may be due to animal and some human contamination. Conductivity at Meadow Park Bridge was also high, indicating higher dissolved and particulate water content from other stations. Particular sampling attention should now be directed towards this site in order to detect the most probable source of the bacteria and higher conductivity. Deer Creek inflow on July 14 was within the standard deviation of the 200 mpn standard.

Lake Wildwood WWTP

  The Lake Wildwood Wastewater Treatment Plant (WWTP) outfall is located on Deer Creek downstream approximately 1200 feet downstream from the spillway. Average daily WWTP flows measured from 2000 – 2003 ranged from 0.36 to 1.51 MGD (0.5 to 2.33 cfs), and the average dry weather flow was 0.46 MGD (0.71 cfs) (ECO:LOGIC, 2004). The WWTP effluent is a source of nutrients and organics, and has exceeded California Toxics Rule (CTR) water quality criteria for constituents of concern (as defined by the CTR) including nitrate, pH, copper, silver, and trihalomethanes (THMs). However, no ambient concentrations of these constituents were found in either the Yuba River or Deer Creek ambient samples, indicating that the assimilative and diluting capacity for them exists in these receiving waters.

  The NPDES permit for the Lake Wildwood WWTP also stipulates that the ambient temperature of Deer Creek and downstream waters cannot increase by more than 5 degrees Fahrenheit due to treated effluent from the Lake Wildwood WWTP. Temperature differences exceeding this criterion were observed on at least 10 occasions from January 2001 through December 2002, in weekly measurements taken at locations upstream and downstream of the effluent discharge point. These exceedances were most likely caused by insufficient assimilative capacity in Deer Creek for temperature (ECO:LOGIC, 2004). As part of the new NPDES permit for expansion of the Lake Wildwood WWTP, a detailed habitat assessment of Deer Creek will probably be required by the Regional Water Quality Control Board.

  Friends of Deer Creek Lake Wildwood Monitoring Report

  Major concerns have been expressed by the Friends of Deer Creek during the fall drawdown period (Friends of Deer Creek, 2005). Their major concerns are water temperature and turbidity in Deer Creek. The Friends of Deer Creek are to be congratulated for sampling the creek and reporting on the conditions they observed. The fall drawdown procedure has been refined during the 3 years since the Regional Board’s Notice of Violation was received in 2000. Turbidity and temperature were the major concerns, as well as dissolved oxygen. The last drawdown operation (Lake Wildwood, 2004) maintained a temperature range which was less than the natural fluctuation measured to establish the ambient conditions prior to discharge. Water temperature monitoring at the discharge point weir and at points downstream and in the Yuba mainstream are necessary to evaluate effects for a specific drawdown event; however, averaging water temperatures over a 4 year period can be misleading in the evaluation of temperature exceedance due to the variable nature of ambient temperature in Deer Creek. This can disguise improvements in temperature regulation due to refinements in the discharge release hydrograph between 2001 and 2004.

  Deer Creek has a natural and highly variable seasonal flow regime, and turbidity as well as temperature is extremely variable as well. See Appendices 1 – 2 for our plotting of their temperature and turbidity data from Sites 2 and 4 above and below Nevada City and Sites 6 and 7 above and below Lake Wildwood. Although the initial release in the fall drawdown procedure has caused turbidity to exceed the permit requirements of a 1 NTU increase (where natural turbidity is between 0 and 5 NTUs), the changes are within the natural variability of Deer Creek  (Appendix 3), and refinements in the release timing and amount have reduced the turbidity over the three previous years. The drawdown procedure mimics high-flow storm events which occur with increasing frequency from mid-October through the wet season. The potential for methyl mercury and other contaminant transport via suspended solids, and potential effects on benthic macrofauna community structure and other aquatic organisms (e.g. beaver and possibly river otter) are inherent in this highly variable system.

  Concerns have also been raised regarding the effects of the fall drawdown release flows on Fall-run Steelhead trout and Spring-run Chinook salmon, both found as far as a quarter mile up Deer creek from the confluence of the Yuba River and both federally protected species. The spawning period for both of these species overlaps at the time of the Lake Wildwood release, and salmonids have been observed being drawn up Deer Creek to spawn beyond a safe range, i.e. to inundated areas upstream which potentially dry up upon return to lower flows, so that the eggs dry out before the onset of the wet season. In other similar systems with great hydraulic variability, salmonids have been genetically imprinted not to spawn during the first freshets for this reason. The California Department of Fish and Game is studying the potential for bringing spawning gravel to the lower reaches of Deer Creek near the confluence in order to keep fish from moving beyond the safe range.

Higher Plant Problems and Remedies

  Highly productive lakes like Wildwood inevitably have problems with algae and/or higher aquatic plants. Most modern lake dwellers are forced to deal with either or both of these problems during the warmer months of the year. During a visit by the principle investigator on the 5^th of August a survey of aquatic plant growth was made of the entire lake. Patches of higher plants were beginning to develop where clearer water conditions existed. The boat marina had a healthy bloom of unicellular algae which was sufficient to shade out most of the higher plant growth, illustrating the reality that you can have a fairly green lake without a serious higher plant growth or a clearer lake with emergent plants. Local conditions such as nutrient and sediment inputs tend to dictate which conditions will be present at any given time.

  Aquatic weed harvesting is often essential where boat traffic or swimmers must contend with emergent plant growth. A problem with mowing is of course the dispersion of fragments to take root in new areas. Skimming will reduce but never eliminate this problem associated with mowing.

  Four different higher aquatic plant species were collected during the 5 August 2005 survey. These were identified by an aquatic weed specialist as:

Floating Pond Weed – Potomogeton natans

Watermillfoil – Miriophyllum sp.

Coontail – Cerutophyllum demerum

Najas – Natas guadalupensis

Additional sampling will be required to determine if Eurasian millfoil is the millfoil species present. 

Management Strategy

          First of all it should be reported to the home owners that as artificial lakes of this  type go which are:  1)surrounded by housing development, 2) has a  golf course, 3)  has inflow from a stream receiving effluent from a treatment plant servicing a small town up stream, and 4) has pasture on the watershed, the lake is actually in excellent condition. We have already described the fact that one can have a green, healthy lake with significant phytoplankton or a clearer lake with higher aquatic plant infestation. Under what limnologist call hypereutrophic conditions you can even have solid mats of bluegreen algae shading out the more beneficial forms of algae (green algae and diatoms). Wildwood Lake has a reasonably balanced fertility that is probably slowly edging up toward more eutrophic conditions as nutrients gradually build up in the bottom waters of the lake. For this reason we recommend the following management during the rest of  2005 and the Winter and Spring of 2006.

1)      We recommend that the lake not be dewatered during the Fall of this year. This recommendation is based on the fact that down stream considerations will not be altered by dewatering and time will allow for a more effective lake management plan to be developed  which we envision  combining hypolimnetic discharge with surface runoff blending. This has the advantage of reducing the overall nutrient content of the lake which will slow  the process of eutrophication, raise oxygen content of the deeper water, which in turn will reduce the internal loading of nutrients from the rich sediments collecting on the bottom of the lake.

2)      We recommend that an upstream survey of Deer Creek be made from above Nevada City to Lake Wildwood with attention given to possible improved erosion control in the .watershed.

3)      Sampling of inflow and outflow water to the lake should demonstrate conclusively that water quality is actually improved by the presence of the lake. This should be done during periods when the lake is overflowing into lower Deer Creek.

4)      Alterations in current monitoring of the lake are recommended as follows.

a.      Oxygen profiles at the outflow structure and at the midlake stations 3 and 4 (figure 2 should be done at five foot intervals.

b.      Coliform sampling should be continued with the addition of Millipore paddles With more intensive sampling at the beaches during summer months.

c.      With increasing concern over the possibility of an increase in West Nile Virus in California , we recommend that careful attention be given to any standing water sources which are in anyway isolated from lake wave action. Old tires, cans, treeholes and stagnant water in depressions near shore or where emergent higher plants like cattail isolate small patches of water near shore should be sprayed during the summer months. Particular attention should be given to any dead birds seen in the area. Should they be encountered they should be bagged up and delivered to the local health authorities for analysis for West Nile.

d.      Investigation should be made with the authorities as to the possibility of isolating by curtaining off small patches of higher plants near shore for herbicide application. Sonar could be used for this purpose and it might prove very effective around boat and swimming docks where weed harvesting can only be done by hand.

e.      Lake Wildwood residents can do a lot to protect their extraordinarily valuable lake resource for this and future generations. ERA will in the near future prepare a set of guidelines for “Modern Lake Dwellers” towards this end.

References

ECO:LOGIC. 2004. Nevada County Sanitation District No. 1. Lake Wildwood Wastewater Treatment and disposal facilities Plan. April 2004. Prepared for Nevada County Department of Transportation and Sanitation.

ERA. 2005. Lake monitoring on May 19, 2005.

Friends of Deer Creek. 2005. Lake Wildwood Monitoring Report. Prepared by Friends of Deer Creek, May 2005.

Horne and Goldman.1994. Limnology, 2^nd Edition. McGraw Hill.

Lake Wildwood, 2003. Lake Wildwood Report of Water Quality Parameters During the Fall Drawdown of the Lake, 2003. Prepared for the Lake Wildwood Association, December 1, 2003.

Lake Wildwood, 2004. Lake Wildwood Report of Water Quality Parameters During the Fall Drawdown of the Lake, 2004. Prepared for the Lake Wildwood Association, December 1, 2005.

Workplan. 2001. Workplan for Lake Wildwood Fall Drawdown. Submitted to California Regional Water Quality Control Board, Central Valley Region. January 19, 2001.