3800 RIVERFRONT BLVD 2025-07-23 - Laserfiche WebLink

1 1 1 1 1 1 1 1 1 i� 1 1 1 1 LJ 1 Design and Installation Specifications Size the pipe to convey the flow. The capacity for temporary drains shall be sufficient to handle the peak volumetric flow rate calculated using a 10-minute time step from a 10- year, 24-hour storm event, assuming a Type 1A rainfall distribution. Alternatively, use 1.6 times the 10-year, 1-hour flow indicated by an approved continuous runoff model. Consult local drainage requirements for sizing permanent pipe slope drains. • Use care in clearing vegetated slopes for installation. • Re-establish cover immediately on areas disturbed by installation. • Use temporary drains on new cut or fill slopes. • Use diversion dikes or swales to collect water at the top of the slope. . Ensure that the entrance area is stable and large enough to direct flow into the pipe. • Piping of water through the berm at the entrance area is a common failure mode. . The entrance shall consist of a standard flared end section for culverts 12 inches and larger with a minimum 6-inch metal toe plate to prevent runoff from under- cutting the pipe inlet. The slope of the entrance shall be at least 3 percent. Sand bags may also be used at pipe entrances as a temporary measure. . The soil around and under the pipe and entrance section shall be thoroughly com- pacted to prevent undercutting. . The flared inlet section shall be securely connected to the slope drain and have watertight connecting bands. • Slope drain sections shall be securely fastened together, fused or have gasketed watertight fittings, and shall be securely anchored into the soil. . Thrust blocks should be installed anytime 90 degree bends are utilized. Depend- ing on size of pipe and flow, these can be constructed with sand bags, straw bales staked in place, "t" posts and wire, or ecology blocks. . Pipe needs to be secured along its full length to prevent movement. This can be done with steel "Y' posts and wire. A post is installed on each side of the pipe and the pipe is wired to them. This should be done every 10-20 feet of pipe length or so, depending on the size of the pipe and quantity of water to divert. . Interceptor dikes shall be used to direct runoff into a slope drain. The height of the dike shall be at least 1 foot higher at all points than the top of the inlet pipe. . The area below the outlet must be stabilized with a riprap apron (see BMP C209: Outlet Protection (p.356), for the appropriate outlet material). . If the pipe slope drain is conveying sediment -laden water, direct all flows into the 2014 Stormwater Management Manual for Western Washington 1 Volume 11 - Chapter 4 - Page 343