Construction of small check dams across a swale or ditch reduces the velocity of concentrated flow and dissipates energy at the check dam. The reduced velocity slows sediment transport and erosion. They may be used where temporary channels or permanent channels are not yet vegetated, channel lining is infeasible, and velocity checks are required. The dam should form a triangle when viewed from the site. This prevents undercutting as water flows over the face of the dam rather than falling directly onto the ditch bottom.
Establishing a Check Dam
Check dams should be faced perpendicular to the flow of water.
Keep the maximum height at 2 feet at the center of the dam.
Keep the center of the check dam at least 12 inches lower than the outer edges.
Keep the side slopes of the check dam at 2:1 or flatter.
Key the stone/sandbag into the ditch banks and extend it beyond the abutments a minimum of 18 inches to avoid washouts from overflow around the dam.
Sand Bag Check Dam (temporary)
Triangular Silt Dike (temporary)
Silt dikes are triangular foam devices wrapped in a geotextile fabric, which extends 2-3 feet beyond the edges of the dike. A typical length is 7 feet, but several may be put end to end. Silt dikes may be used as a check dam for perimeter protection, for temporary soil stockpile protection, for drop inlet protection, or as a temporary interceptor dike.
TDS Also Used For…
Sediment Ponds
Diversion Ditches
Concrete Washout Facilities
Curbing
Water Bars
Level Spreaders
Berms
Rock Check Dam (temporary or permanent)
Limitations
Check dams may not be placed in streams unless approved by the State Department of Fish and Wildlife (WDFW). Check dams may not be placed in wetlands without approval from a permitting agency. Contact the WDFW or Whatcom County Critical Areas staff for further information.
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 over wintering juvenile salmonids and emergent salmonid fry.
Maintenance Requirements
Check dams shall be monitored for performance and sediment accumulation during and after each runoff producing rainfall. Sediment shall be removed when it reaches one-half the sump depth.
Anticipate submergence and deposition above the check dam and erosion from high flows around the edges of the dam.
If significant erosion occurs between dams, install a protective riprap liner in the portion of the channel.
Storm Water Management Manual for Western Washington, BMP Reference (2005):
