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Everett School District— Bus Facility <br /> March 24, 2006— Storm Drainage Report <br /> Page 6 _ <br /> range parking lot, a portion of the 8CP Street SW right-of-way, and the above <br /> mentioned wetland. <br /> Stormwater exits the type 2 catch basin through an 18" CMP pipe toward the north- <br /> northeast for approximately 200 feet before reaching another type 2 catch basin <br /> structure. The type 2 catch basin structure is located in the driving range field area <br /> approximately 25 feet north of the driving tees. It was not possible to open this <br /> structure during the downstream analysis. Stormwater continues north through an <br /> undermined sized pipe along and under the driving range area for approximately 800 <br /> feet and exits into an open detention pond. It Is currently unknown who owns and is <br /> responsible for maintenance of the detention pond. <br /> The detention pond is located just off the northeast corner of the driving range. Please <br /> see Figure 2 Downstream Flow Path on next page for location of the off site detention <br /> pond. Access to the detention pond is from an access road along the east side of the <br /> driving range. The detention pond clearly had not been maintained and was overgrown <br /> with vegetation. Sediment was built up under the surface of water and the control riser <br /> was not functioning properly. The control riser was rotated approximately 30 degrees <br /> from vertical. Built up sediment covered the bottom orifice of the control riser. The <br /> released stormwater Flows were not constant. Stormwater released from the control <br /> hser outlet In a repetitive manner, i.e. a small amount of water flow would exit every <br /> couple of seconds. <br /> ` Stormwater exiting the control riser was airborne and dropped approximately 3 to 4 feet <br /> before reaching a scoured and eroded channel, most likely from stormwater released in <br /> a repetitive manner. The released stormwater fell onto a steep bank with a slope of <br /> approximately 1 horizontal to 1 vertical. There was no evidence of a rock or rip-rap pad <br /> to reduce the energy of the exiting stormwater. The channel was scoured and eroded <br /> for approximately the first 10 feet and became a more apparent channel with a square <br /> cross-section containing a width and height of approximately 2 feet. This point is <br /> beyond the downstream 1/4 mile and where the downstream analysis was concluded. <br /> f <br />