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2.3 Past Analyses. _ Twin Lake has been included in several past hydrologic studies. In the Hvdrolo is Anal sY is Of Lakes and Open Space in Ramsey County (1975, Barr), overflow drainage from the Vadnais Lake system is projected to flow into Twin Lake during severe rainstorms. This study described the outlet control elevation for Twin Lake as being 874 feet MSL, and the lowest home's elevation as being at 876 feet. At such Time as the upstream watershed should be completely converted to urban-style Land use, the 197 study projected a need for Twin Lake to be able to discharge 63 cfs in order for it not to exceed a projected maximum allowable elevation of 875 feet. The report also recommended lowering ~ the outflow control elevation to 871 feet. The Phalen Chain of Lakes Surface Water Management Plan (1988, Barr) describes Twin Lake's position within the County Ditch 16 system. A detailed study of the lake's hydrology was not included, but the report states that the lake will overflow to County Ditch 16 during very large storms or snowmelt periods at an outflow rate of 63 cfs, based on the 1975 study. Since the city of Vadnais Heights lies just to the north of Twin Lake, the lake is affected by water management plans for that municipality. The Surface Water Management Plan for the City of Vadnais Heights, developed by Short, Elliott & Hendrickson Engineering Company.(SEH) in 1989 shows Twin Lake receiving overflow drainage from both the east and west portions of Vadnais Lake. Barr was not able to verify an existing connection between the Twin Lake watershed and west Vadnais Lake during this study. The SEH report asserts that a maximum of approximately 10 cfs will flow from Twin Lake during the 100-year high-water event (assuming a high normal level, discussed below). 2.4 Water Quality Considerations Twin Lake currently demonstrates water quality conditions that are good for a metropolitan lake. This water quality owes largely to the regional topography and local geology which isolates the lake hydrologically from nearby water bodies and watersheds. It currently receives runoff only from its own watershed, which is small relative to the lake's volume. In addition, much of the lake's watershed remains in its natural_ state, so that degradation of the Lake due to human activities has remained minimal. The lake's present loading rate of pollutants and fertilizers is relatively low. 23162\264\TWINLAKE.RPT\I~h~i 3