1710 W MARINE VIEW DR 2024-01-03

. Maximum 3H A V interior side slopes and maximum 2H:1 V exterior slopes. The interior slopes can be increased to a maximum of 2H:1 V if fencing is provided at or above the maximum water surface. . One foot of freeboard between the top of the riser and the crest of the emergency spillway. • Flat bottom. . Minimum 1-foot deep spillway. . Length -to -width ratio between 3:1 and 6:1. Sediment Pond Discharae The outlet for the pond consists of a combination of principal and emergency spillways. These out- lets must pass the peak runoff expected from the contributing drainage area for a 100-year storm. If, due to site conditions and basin geometry, a separate emergency spillway is not feasible, the prin- cipal spillway must pass the entire peak runoff expected from the 100-year storm. However, an attempt to provide a separate emergency spillway should always be made. Base the runoff cal- culations on the site conditions during construction. The flow through the dewatering orifice cannot be utilized when calculating the 100-year storm elevation because of its potential to become clogged; therefore, available spillway storage must begin at the principal spillway riser crest. The principal spillway designed by the procedures described below will result in some reduction in the peak rate of runoff. However, the design will not control the discharge flow rates to the extent required to comply with 1-3.4.7 M R7: Flow Control. The size of the contributing basin, the expected life of the construction project, the anticipated downstream effects, and the anticipated weather con- ditions during construction should be considered to determine the need for additional discharge con- trol. Principal Spillway: Determine the required diameter for the principal spillway (riser pipe). The dia- meter shall be the minimum necessary to pass the peak volumetric flow rate using a 15-minute time step from a Type 1 A, 10-year, 24-hour frequency storm for the developed condition. Use Figure 1I- 3.31: Riser Inflow Curves to determine the riser diameter. To aid in determining sediment depth, one -foot intervals shall be prominently marked on the riser. Emergency Overflow Spillway: Size the emergency overflow spillway for the peak volumetric flow rate using a 10-minute time step from a Type 1 A, 100-year, 24-hour frequency storm for the developed condition. See BMP D.1: Detention Ponds for additional guidance for Emergency Over- flow Spillway design Dewatering Orifice: Size of the dewatering orifice(s) (minimum 1-inch diameter) using a modified version of the discharge equation for a vertical orifice and a basic equation for the area of a circular orifice. Determine the required area of the orifice with the following equation: As(2h)o.a A° 0.6 x 360OT90-5 where Ao = orifice area (square feet) 2019 Stormwater Management Manual for Western Washington Volume 11- Chapter 3 - Page 390