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and two garages on the west side of the lake within the 100-year flood plain and an additional four homes lower than Elevation 993.0 (the minimum building elevation for land adjacent to FF Silver Lake): F Drawdown of Silver Lake occurs quickly compared to downstream lakes. This means that the lake does not hold excess stormwater long enough to be of significant value in reducing downstream flooding. Although the lake drains quickly, residents are very sensitive to small changes in lake level. Silver Lake water level data from 1925 to the present is available from Ramsey County. Currently, a volunteer measures the Silver Lake water level every week and submits the data to Ramsey County. Silver Lake's maximum, minimum and average annual water levels for the years 1925 through 1992 are shown on Figure 4-1. VBWD, North St. Paul, Maplewood and Ramsey County are all aware of an intercommunity issue involving a ditch erosion problem upstream of Silver Lake. Located in North St. Paul, the ditch drainage system carries water from a wetland in Maplewood, north of Silver Lake, to the northwest shore of Silver Lake. This ditch is located completely within the limits of one property owner. The ditch is eroding and a sediment delta is forming in Silver Lake at the ditch outfall. The approximately 2-acre wetland in the City of Maplewood lies north of Lake Boulevard/Joy Road (Ramsey County Road 109) and west of Lydia Avenue. As part of a road improvement project in 1990-1991, the City of Maplewood replaced the wetland's outlet pipe under Lake Road. The new pipe was placed at the same elevation, and is approximately the same size as the old outlet pipe. However, the old outlet pipe was partially blocked with sediment, thus creating a floe restriction. The flow restriction was relieved when the new pipe was installed. As a result, the wetland water level dropped and, according to the property owner, more water discharges into the ditch, causing more erosion. 4.2.1.3 VBWD Water Quantity Management Goals As a result of discussions with VBWD and the City of North St. Paul, the City of Maplewood agreed to place a restriction at the upstream end of the outlet pipe from the wetland to help reduce flow rates in the ditch and to raise the water level in the wetland. VBWD has not been able to confirm if the City of Maplewood completed this work. However, reducing the outflow may not be enough to eliminate the erosion problem. Therefore, in 1994 or 1995, VBWD will undertake an erosion monitoring program to determine if ditch erosion is still occurring. The major erosion areas along the ditch will be identified and monitored over a six- to twelve-month period. Cross -sectional survey data will be used to determine the annual sediment yield from the ditch banks. The extent of the sediment delta will also be surveyed at the beginning and end of the monitoring period to determine if additional sediment beyond the ditch erosion, is entering Silver Lake. It is possible that the sediment delta is the result of sediment from sources other than ditch erosion. If the monitoring results indicate that the ditch is still eroding and is the major contributor of sediment to the sediment delta; VBWD will need to institute a project to address the erosion problem. The project would involve either piping the flow from Lake Boulevard to Silver Lake or repairing/restoring the ditch with riprap. Another possible solution which may be investigated involves planting woody plants on the ditch banks to stabilize the banks and prevent erosion. A careful analysis of the ditch hydrology is necessary, and other measures, such as flow deflection, may be needed in conjunction with the vegetation for this method to be successful. 23\82\045\SEC4.RPT\KMH 2 DRAFT: June 23, 1994