Lake May Holds Almost as Much Muck as Water

On November 16 and 17, 2005, field personnel from Environmental Research & Design worked their way around Lake May in Winter Haven and stopped at 167 separate locations. At each one they took two measurements, and each site was fixed by longitude and latitude with a portable GPS device.

The first measurement was the water depth. They lowered a 20 cm diameter Secchi disk on a graduated line until it met resistance from the surficial sediment layer, and recorded the depth on the line. Through the central portions of the lake that came to approximately 8-10 ft.

Then they put a 1.5-inch diameter graduated aluminum pole over the side and forced it down into the sediments until it reached firm bottom material, typically sand or clay. That is the depth to the firm lake bottom. The difference between the two numbers is the depth of unconsolidated sediment — the muck.

Through most of Lake May that difference runs approximately 6-10 ft. In one isolated pocket along the northwest side, next to the inflow from Lake Howard, the muck extends as deep as 18 ft. In the residential canals along the west side of the lake it is thinner, approximately 1-4 ft.

Added up, the organic sediments sitting above the firm bottom of Lake May come to approximately 302.4 ac-ft, or 487,872 cubic yards. Table 2-1 of the study puts the lake itself at a surface area of 50.54 ac and a volume of 316.0 ac-ft, measured at a water surface elevation of 131.79 ft. Approximately 50% of the lake bottom carries organic muck 7 ft deep or more. Spread evenly across the entire lake bottom, the muck would be approximately 5.98 ft deep.

Nobody had measured it before. The most recent bathymetry available for Lake May was a study conducted by USGS during March 1977, and it provided water depths only; it did not attempt to quantify existing muck accumulations.

Over the preceding decade, alum stormwater treatment systems, wetland treatment systems and wet detention ponds had been constructed to control nonpoint source inputs entering the Winter Haven Chain-of-Lakes. Environmental Research & Design framed the problem those projects left open: continued nutrient release from the accumulated sediments may negate the water quality improvements the projects could otherwise achieve. The study set out to determine whether all or portions of the accumulated organic sediments in Lakes May, Shipp and Lulu must be removed to achieve the desired water quality in them.

The study also estimated what would be left if the muck came out. With the organic muck removed, Lake May would become a relatively deep lake, extending to depths of approximately 18-19 ft in central portions.