- Lake Forest Association (LFA) - Caretakers of Eastwood Lake in Chapel Hill, NC.
Our Late Summer/Labor Day, 2016, water samples were taken Wednesday, August 31, 2016 between 10:45 and 11:15 AM. This is our fourth, last regularly scheduled water test this year.
#1 Dock 4 cfu
#2 Cedar Fork Creek 4 cfu
#3 Booker Creek 4 cfu
Caution level is individual reading above 400 cfu, or average above 200 cfu.
Lake water temperature ranged from 87-89F(31-31.8C). The SECCI clarity reading was 14 inches, not very clear. The rain gauge was dry. The lake level was 3” below the lowest step on the spillway. We were slightly below full for our July 4 test, then we had steady rainfall for all of July, followed by nothing measurable in August.
The CFU readings continue to be very good! If we have a warm September and lake use remains steady, we may run one more test this year.
We are having a mild late season algae bloom. This has not happened for a number of years, but it has happened before. It is not a serious problem. The water in the still areas is less pleasant than it is in the main areas of the lake where there is regular swimming, boating, and birds and fish keeping the water moving. The water samples were mostly clear without much suspended debris or any significant color. Swimmers in the lake at the time of my sampling indicated the “thermocline” (area of cool water below the surface) was very noticeable beyond the far dock. This means we are still getting good inflow from the several springs in the bottom of the lake located in the main bay, to the left of a line from the swimming beach to the gazebo on the far shore. Although there was only seepage going over the dam, there is good outflow below the dam, water continues to move through the lake.
It seems like the near dock has permanently moved about 25-30 yards left of its previous location. Our main water sample location is just beyond that former dock location. That site is both the deepest point in the lake, and the location of the confluence of the two surface streams that “make” Eastwood Lake. These are Cedar Fork Creek (across the lake to the right from the beach) and Booker Creek (far to the left end, beyond the delineated wetland (swamp) and external forebay near the intersection of North and South Lakeshore Drives. We take three samples (normally), one at the “old” dock location, and one closer to each tributary source. The reasoning for this is: If we ever get a high reading at the main (dock) location, the other samples will help us determine where the contamination is coming from. In the past we also have conducted upstream tests in the tributaries, but this has not been necessary since the lake was refilled after the last restoration in 2003.
What we test for does not “grow” in the water, so it will always be going to a lower reading unless there is fresh contamination. Sewage and animal waste runoff from the ground are the primary sources for the Fecal Coliform that we test. Our watershed is about 4 square miles, mostly to the North and West of the lake. As development occurs, our watershed area does not change, but water runs faster and farther as the ground becomes more impervious due to pavement and buildings. Unimproved ground acts as a filter. The slower the water runs, both contamination and erosion have a chance to “settle out” before reaching our lake. The forebays at both inlets are designed to slow the water before it reaches the main part of the lake.
Eastwood Lake was created in the 1930s by the CCC. There are no natural permanent lakes in this area. Normally any lake that would occur after a big storm would “silt in” (eutrophication) in a few years because of our soil types. After Lake Forest development began, Eastwood Lake was drained and “dredged” about three times at 20-30 year intervals, each time hoping for a “permanent fix”. This was never a welcome event or expense. By the middle 1990s we knew more about soil and lakes, and realized that we would always need to maintain the lake, no one-time fix would work. We worked with the UNC Geology department and an engineer to come up with a solution that is essentially similar to what was done with Jordan Lake. We now have forebays to slow the water coming in to the lake, acting as silt-catchers. We also have “standpipes” near the dam which will allow the lake to be lowered partially to one of two levels without fully draining it and killing fish in order to work on retaining walls and remove any silt that is accumulating near the shore. All of this increases the time interval between when the lake needs to be fully drained to remove accumulated silt.
When we last restored the lake, the engineer estimated it would take 2-2.5 inches of rain in our watershed to fill the lake. We had a drought that summer, then got 2.5 inches in September. That half-filled the lake. The ground was parched from the drought. After first rain saturated the ground, 1.3 inches of rain finished filling the lake about 2 weeks later.
In terms of the annual cycle of algae blooms, these are also normal cycles. The human contribution to this is mostly fertilizer runoff. Anyone who lives near the lake should use a “lake margin” fertilizer which has less phosphorous that other types. Phosphates are held in the soil, so the only time they are really needed is when new soil is added (or old soil is removed). Whenever anyone near the lake fertilizes, it needs to be applied lightly and “watered in”, never before an expected rain storm. Phosphates stimulate algae. If you use a lawn maintenance service, discuss this with them. If there are questions, have them contact NCSU or Orange County Ag. Extension, http://www.soil.ncsu.edu/programs/waterquality/
There is also helpful information on this website: http://lakeforestassociation.org/taking-care-of-our-lake/
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