Laserfiche WebLink
Watershed and Lake Response Modeling <br />Watershed Model. As in the case of Langton, the PONDNET was used to estimate runoff- <br />generated phosphorus entering Bennett. For more information on the PONDNET model refer to <br />the Langton Lake section on modeling. Table 4 in Appendix A shows results from the <br />PONDNET model for Bennett Lake. By model estimates, Bennett receives an average annual <br />phosphorus load of about 540 pounds from its watershed. Total phosphorus loading per acre of <br />lake is estimated at about 201bs (more than double the loading per acre for Langton Lake) and <br />reflects much higher inputs than the lake can reasonably be expected to absorb and stay healthy. <br />Phosphorus removal efficiencies for ponds in the Bennett watershed range from 37% to 56 %. <br />Ponds WP -1 and BL -4 serve important roles in treating stormwater that eventually reaches <br />Bennett Lake. Modification to increase the standing water volume of ponds in the watershed <br />may be a cost - effective strategy to enhance the stormwater treatment functions of these ponds <br />and decrease watershed phosphorus loads reaching Bennett Lake. Improvement efforts should <br />focus on those ponds that receive runoff from large drainage areas and whose model estimated <br />removal efficiencies are low (less than 40 -50 %). <br />Lake Response Models: Total phosphorus and water loading rates from PONDNET along with <br />the actual measured growing season mean phosphorus level was used as input to the WiLMS <br />model in order to estimate in -lake phosphorus concentrations (Appendix A, Table 6). For more <br />information on the WiLMS model refer to the Langton section on modeling. The Rechow, 1979 <br />general model provided the best fit for the data with measured mean phosphorus concentration of <br />140 ug /1. <br />In a fashion similar to Langton, hypothetical changes in phosphorus concentrations resulting <br />from percent reduction in phosphorus loadings were calculated. In the case of Bennett Lake, a <br />40% reduction in phosphorus loads would be needed in order to bring in -lake water quality up to <br />Grade C on the Met Council's scale. This is a very large reduction and is likely to be achieved <br />only with significant and expensive infrastructure changes and intensive management activities <br />in the lake itself. <br />City of Roseville 53 <br />Parks Natural Resource Management <br />