Laserfiche WebLink
Broadway Everett Expansion Storm Drainage Report <br /> November 16, 2022 <br /> V=27 x 0.036 x (1/2) =0.486 ft/s <br /> Tc= 333/(60 x 0.486) = 11.42 min <br /> i= 3.69/11.420.156= 0.95 in/hr <br /> Q = (0.90) * (0.95 in/hr) * (0.577 ac) = 0.49 cfs <br /> The 2-year flow of the site is 0.49 cfs and the resulting surface area (SA) of the sediment trap is <br /> 1,019 sf. The sediment trap shall be lined with a minimum 20 mil PVC liner per the geotechnical <br /> engineer recommendation. <br /> SA= (2080 sf/cfs) * (0.49 cfs) - 1,019 sf <br /> The principal spillway for the sediment trap is sized using guidance from BMP 241 Sediment Pond <br /> and Figure II-3.31: Riser Inflow Curves from the DOE manual. The 10-year peak volumetric flow <br /> rate, Q, is 0.75 cfs, but a more conservative 1 cfs is used. The head, H, is 3.5 ft. <br /> Using the equation Q = 9.739*D*H3/2 from Figure II-3.31, the riser diameter, D, was calculated to <br /> be 0.016 ft, or 0.19 in. The sediment trap will have an outlet spillway with a 1 ft depth and 6 ft <br /> width, meeting the minimum dimensions on Figure II-3.27 from BMP 240. With the proposed <br /> spillway dimensions, the minimum calculated requirements are met and exceeded. <br /> 4. Install Sediment Controls <br /> Perimeter protection will be provided in the form of silt fence (BMP C233) and straw wattles (BMP <br /> C235). A sediment trap (BMP C240)will also be implemented to contain runoff in the construction <br /> area. <br /> 5. Stabilize Soils <br /> Exposed soils will be limited to the building foundation, utility trenching and pavement restoration. <br /> Landscaped surfaces will be given topsoil per BMP C125, and other exposed soils will be mitigated <br /> with plastic covering per BMP C123 as necessary. The entire site will apply dust control per BMP <br /> C140 during dry weather periods. <br /> 6. Protect Slopes <br /> N/A—All cut and fill slopes will be designed, constructed, and protected in a manner that minimizes <br /> erosion. <br /> 7. Protect Drain Inlets <br /> All catch basins on-site that are outside of the proposed building footprint will be protected with <br /> Storm Drain Inlet Protection per BMP C220 for the duration of the project. <br /> Page 10 <br />