3214 BROADWAY BROADWAY KINECT APARTMENTS 2021-08-11

4111 CITY OF EVERETT STORMWATER MANAGEMENT MANUAL • 1111 r 12. Level spreaders, when installed every so often in grassy swales, keep the flows from concentrating. Materials that can be used include sand bags, lumber, logs, concrete, and pipe. To function properly,the material needs to be installed level and on contour. Maintenance Standards 1. The spreader should be inspected after every runoff event to ensure that it is functioning • correctly. • 2. The contractor should avoid the placement of any material on the structure and should prevent • construction traffic from crossing over the structure. • 3. If the spreader is damaged by construction traffic, it shall be immediately repaired. 3.3.8 BMP C207: Check Dams • Purpose • Construction of small dams across a swale or ditch reduces the velocity of concentrated flow and • dissipates energy at the check dam. • Conditions of Use St 1. Where temporary channels or permanent channels are not yet vegetated, channel lining is infeasible, and velocity checks are required. • 2. Check dams may not be placed in streams unless approved by the WDFW. Check dams may not • be placed in wetlands without approval from a permitting agency. • 3. Check dams shall not be placed below the expected backwater from any salmonid bearing water between October 1 and May 31 to ensure that there is no loss of high flow refuge habitat for • overwintering juvenile salmonids and emergent salmonid fry. • Design and Installation Specifications • 1. Whatever material is used,the dam should form a triangle when viewed from the side. This • prevents undercutting as water flows over the face of the dam rather than falling directly onto the • ditch bottom. • 2. Check dams in association with sumps work more effectively at slowing flow and retaining sediment than just a check dam alone. A deep sump should be provided immediately upstream of • the check dam. it 3. In some cases, if carefully located and designed, check dams can remain as permanent installations with very minor regrading. They may be left as either spillways, in which case • accumulated sediment would be graded and seeded, or as check dams to prevent further sediment from leaving the site. • 4. Check dams can be constructed of either rock or pea-gravel filled bags. Straw bales are not an • allowed construction material. Numerous new products are also available for this purpose. They tend to be reusable, quick and easy to install,effective,and cost efficient. • 5. Check dams should be placed perpendicular to the flow of water. 6. The maximum spacing between the dams shall be such that the toe of the upstream dam is at the • same elevation as the top of the downstream dam. • 7. Keep the maximum height at 2 feet at the center of the dam. • ID • Volume II—Construction Stormwater Pollution Prevention 3-46