2003-08-14_AgendaPacket - Laserfiche WebLink

Home

3.3 Regional Groundwater Elevations and Twin Lake ~egionai groundwater maps show Twin Lake to be approximately at the level of the local water table. Curiously, the normal water elevation. of Twin Lake remains approximately 12 feet below the water Level of neighboring Vadnais Lake, just 500 feet away. The maintenance of this head difference between the Lakes apparently owes to the low permeability of fine glacial drift underlying the higher Vadnais Lake. 3.4 Overflow from Vadnais Lake To evaluate the likelihood of flooding at Twin Lake, the likely flow to the take from neighboring Vadnais Lake must be estimated. Vadnais Lake is the last in the chain of lakes utilized by the Saint Paul Water Utility for conveyance and storage of water for the city's drinking water supply. The SPWU pumps water from Vadnais Lake daily, anal controls flow into Vadnais Lake through regulation of pumping from the Mississippi River into the chain of lakes leading to Vadnais Lake. Because it .is used as a reservoir for the city, the water levels in the lake are closely monitored and controlled. In addition, due to water quality considerations, SPWU officials are reluctant to allow water from Vadnais to flow into Twin Lake. The policy of the SPWU is to maintain the water Ievel of the lake between 882.0'7 and 884.1'7 feet in order to maintain sufficient storage but prevent overflow to Twin Lake; the outlet from Vadnais to Twin Lake is at Elevation 884.6. Flow from Vadnais to Twin Lake is insignificant and occurs rarely, if ever, according to the SPWU. 3.5 The Twin Lake Watershed The immediate watershed for Twin Lake is relatively small, consisting- of approximately 240 acres. The watershed is bounded on the northeast by Vadnais Lake, on the northwest by the outer edge of a trailer park, and on the southwest by Interstate 694 (see Figure 3). A significant portion of the triangle of Land lying south and east of the Burlington Northern Railroad line (just southeast of the lake), and north and west of Centerville Road currently drains to Twin Lake; this portion is also part of the lake's direct watershed. Three sub-watersheds contributing to Twin Lake were identified through this study: the storm- sewered trailer park area north of Twin Lake Boulevazd, the steeply sloped azea surrounding the lake and consisting primarily of undisturbed land or single family homes, and the triangular basin southeast of the railroad tracks. Using the Bazr surveys, the topographic map commissioned. for this study, and 23\621264\TWINLAKE.RPT1I~i 5