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water quality data. VBWD will consider collecting water quality monitoring data on Weber Pond. 4.2.5 Long Lake Water Management Plan 4.25,1 Location and General Description Long Lake is located in Subwatersheds LNG1 and LNG2, in the Cities of Pine Springs and Mahtomedi. The lake has a surface area of approximately 75 acres and a maximum depth of about 35 feet. Long Lake consists of two separate basins connected by large culverts under Highway 36 and the adjacent service road. The north basin (in Subwatershed LNG1) is DNR #82-118P and the south basin (in Subwatershed LNG2) is DNR #82-371W, In addition, the wetland located north of Long Lake Road is connected to Long Lake by two concrete culverts under the roadway. These culverts are 18 and 15 inches in diameter and are set at Elevation 937.7 and 939,7, respectively (Long Lake's controlled outlet elevation is 937.5). The local tributary area of Long Lake is 1,291 acres, which is comprised of Subwatersheds LNG1, LNG2, and LL5 through LL34. In addition to runoff from its local tributary area, the outflows from Silver Lake (466 acres), Mud Lake (271 acres) and Weber Pond (329 acres) enter Long Lake. Therefore, the total tributary area to Long Lake is 2,357 acres. Figure 2-3 shows the tributary area. 4.2.5.2 Drainage Patterns and Stormwater Issues The Mud Lake and Silver Lake outflows join together in a ditch located in the City of { Oakdale, in the northwest quadrant of the I-694 and T.H. 36 interchange; The combined outflow crosses I-694, enters the City of Pine Springs, and discharges at the southwest shore of the north Long Lake basin, The Weber Pond outflow crosses from the City of Mahtomedi 3' to the City of Pine Springs atLincolntown Avenue through a 15-inch diameter culvert; water ditch is currently a 15- to 20-foot deep ravine. According to residents, the ditch carried water for only one to two months out of the year, prior to the start of development in the upstream R watershed in 1992. Pine Springs residents are concerned that increased runoff volume from upstream development will result in further ravine erosion. VBWD does not have data which shows ravine erosion is occurring or that a sediment delta is forming at the outlet of the ravine. Erosion of Long Lake's steep banks was a major problem, which was made more severe by the large fluctuations in water level which the lake experienced prior to construction of the new outlet in 1987. The lake level fluctuations were due to a small outlet under the old Soo Line Railroad embankment (now the DNR Gateway Trail). Long Lake reached Elevation 943.4 in July; 1978. Figure 4-4, prepare by the DNR, presents historical water level data collected by VBWD from 1969 through the present. The OHW of Long Lake is 939.4. As part of VBWD's Project 1007, the 15-inch corrugated metal culvert was replaced with a new outlet and control structure, located approximately 100 feet northeast of the old outlet. Although the control structure causes Long Lake to act as a regulator for upstream inflows, lake level fluctuations were reduced in magnitude. The Long Lake outlet structure controls the water elevation at 937.5 feet. The outlet pipe crosses the DNR trail embankment located on the south side of the south basin. At its upstream end, the outlet pipe is a 60-inch diameter concrete pipe which leads to the outlet control structure located on the north side of the DNR trail. Within the control structure is a 10-inch diameter orifice which restricts the outflow from the lake until the water level reaches Elevation 941.5, at which .point water begins to flow over a weir. Downstream of the control structure, water flows in a 36-inch diameter corrugated steel pipe 23\82\045\SEC4.RPT\KMH 12 DRAFT: June 23, 1994