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check dams to prevent further sediment from leaving the site. <br />. The maximum spacing between the dams shall be such that the toe of the <br />upstream dam is at the same elevation as the top of the downstream dam. <br />. Keep the maximum height at 2 feet at the center of the dam. <br />. Keep the center of the check dam at least 12 inches lower than the outer edges at <br />natural ground elevation. <br />. Keep the side slopes of the check dam at 2H:1 V or flatter. <br />. Key the stone into the ditch banks and extend it beyond the abutments a minimum <br />of 18 inches to avoid washouts from overflow around the dam. <br />. Use filter fabric foundation under a rock or sand bag check dam. If a blanket ditch <br />liner is used, filter fabric is not necessary. A piece of organic or synthetic blanket <br />cut to fit will also work for this purpose. <br />. In the case of grass -lined ditches and swales, all check dams and accumulated <br />sediment shall be removed when the grass has matured sufficiently to protect the <br />ditch or swale - unless the slope of the swale is greater than 4 percent. The area <br />beneath the check dams shall be seeded and mulched immediately after dam <br />removal. <br />. Ensure that channel appurtenances, such as culvert entrances below check dams, <br />are not subject to damage or blockage from displaced stones. Figure II-4.2.7 Rock <br />Check Dam (p.354) depicts a typical rock check dam. <br />Maintenance Standards <br />Check dams shall be monitored for performance and sediment accumulation during and <br />after each runoff producing rainfall. Sediment shall be removed when it reaches one half <br />the sump depth. <br />. Anticipate submergence and deposition above the check dam and erosion from <br />high flows around the edges of the dam. <br />. If significant erosion occurs between dams, install a protective riprap liner in that <br />portion of the channel. <br />Approved as Equivalent <br />Ecology has approved products as able to meet the requirements of BMP C207: Check <br />Dams. The products did not pass through the Technology Assessment Protocol — Eco- <br />logy (TAPE) process. Local jurisdictions may choose not to accept this product approved <br />as equivalent, or may require additional testing prior to consideration for local use. The <br />products are available for review on Ecology's website at http://www.ecy.wa.gov- <br />/programs/wq/stormwater/newtech/equivalent.html <br />2014 Stormwater Management Manual for Westem Washington <br />Volume 11 - Chapter 4 - Page 353 <br />