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4.2.3.3 VBWD Water Quantity Management Goals Since development is now occurring adjacent to Echo Lake, the additional storage needs to be obtained and the implementation of a project is of high priority. VBWD considered the following two options for obtaining additional storage on Echo Lake: 1. Lower the outlet elevation (normal water level) of Echo Lake by 0.5 feet, to Elevation 995.0, to create additional storage without increasing the 100-year flood level of Echo Lake. In this case, easement acquisition would be unnecessary. Based on the results of a 1992 survey which determined the location of the 995.0 contour in Echo Lake, VBWD decided that the impact of lowering the normal water elevation on the wetland portion of the lake (the southwest side) would be too great. Therefore, this option was rejected. 2. Raise the 100-year flood elevation by restricting the allowable outflow, as stated in the previous VBWD Water Management Plan. Then, additional storage is created by increasing the 100-year flood elevation of Echo Lake to 997.6, approximately one foot above the existing 100-year flood elevation. At the time of development, the Echo Lake Addition developer dedicated drainage easements up to the proposed 100-year flood elevation of 997.6. However, additional easements need to be acquired from the six other Echo Lake shoreline property owners. VBWD believes option 2 is the most feasible option. Based on VBWD's analysis of the watershed, the outlet from Echo Lake is proposed to be a 2-inch diameter orifice at Elevation 995.5 (the existing outlet elevation). Then, the 100-year flood elevation would be 997.6 and the Echo Lake emergency overflow would be the low overflow point near the outlet, at Elevation 997.8. The proposed outlet control structure would be located in a manhole in the same location as the existing outlet pipe. This project is anticipated to be combined with the VBWD will consider monitoring Echo Lake water levels, either using VBWD staff or requesting that the DNR install a gage. 4.2.3.4 Water -Quality and DNR Data Sampling of Echo Lake in 1971, 1972, 1984, and 1991 by the Watershed District and in 1975, 1977, and 1978 by the School District, has shown the lake to have variable, but relatively high phosphorus concentrations and little thermal stratification. Echo Lake currently exhibits relatively poor water quality. Average summer water quality data collected from the lake are presented on Figure 4-3. Data from 1971, 1977 and 1978 are not shown because the sampling occurred in the fall and winter. The 1991 data were compared to criteria used to denote a lake's nutrient "status," and the effects of the nutrients on the general water quality and/or trophic conditions of a water body (HALMS, 1988). Based on a comparison of the lake's nutrient (i.e, total phosphorus) concentration to these criteria, Echo Lake would be assigned a trophic status of hypereutrophic. This means that the lake is extremely rich in nutrients. An evaluation of the effects of the nutrients on the general water quality of the lake (i.e., chlorophyll 4 concentrations and Secchi disc transparency) also results in a hypereutrophic classification. This means that the lake is responding to the nutrient load as expected, and that nuisance algal blooms are a common occurrence. Due to these algal blooms, water transparency is generally poor: 23\82\045\SEC4.RPT\KMH 8 DRAFT:, June 23, 1994