7007 SEAWAY BLVD 2016-01-01 MF Import

2. HYDROLOGY A, Watar dimenslons The hydroperiod fc� Narbeck Swamp and the newly constructed wetland area was calculated using precipitation and evapotranspiration data from the National Weather ' Service for the Everett area in combination with observed streamflow characteristics in the overflow channel. The re�ults of this determination are preserited graphically in Chart 1 on the following page. Since the deeper pond between the exi�ting beaver dam and the leaky berm behaves differently than the shallow ponds downslope of the leaky berm, the graph distinguishes between the two areas. Flood storage capacity is 50,200 cubic feet in 4he winter and 172,000 cubic feet in the summer. Flood storage capacity was calculated for the winter months when there is si.rface flow from Narbeck Swamp, and for the summer months when the only water input is direct precipitation. For the winter months, a baseflow was estimated based on measurements of stream discharge and water depth performed between September 1998 and January 1999. Storage capacity for the summer months was calcuiated on the assumption that all of the area downslope of the leaky berm was dry. The proportion of open water in the new�y created portion of Narbeck Swamp is 42°,6. This was calculated using a statistical sampling method applied to aIl areas within the grading limits of the nroject. Automatic water level monitors were installed to record water depths across the site. These monitors read and record the water level every two hours continuously. Six gauges were installed in open-water portions of the site - one in existing Narbeck Swamp, one in the newly created deep pool, two in the shallow poo� area, one in the overtlow channel, and one at downstream end of the overtlow channel. All automatic gauge locations are shown on the sample point location map (Exhibit 1, in the Map Section at the back of this report). Groundwater levels in the constructed wetland will also be monitored by automatic water level monitors (piezometers). Piezometer locations were coupled with the wetland vege�ation sample plot locations where appropriate, and are thus randomly generated with the exception of piezometer k6 which was coupled with bird census station q3. Piezometer locations are shown on the sample point location map (Exhibit 1 in the Map Section at the back of this report). B. Flow eatterns Major flow pathways were observed throughout the winter. The ieaky berm will be fully activated Sp�ing of 1999 when a binding root mass develops in constructed � 9