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*Check dams are suitable only for a limited drainage area (generally 10 acres or less).
 
*Check dams are suitable only for a limited drainage area (generally 10 acres or less).
 
*Check dams are intended for use in small open channels, not streams or rivers.
 
*Check dams are intended for use in small open channels, not streams or rivers.
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*Hydraulic capacity of the channel can be reduced when check dams are in place.
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*Check dams may create turbulence downstream, causing erosion of the channel banks.
 +
*Ponded water may kill grass in grass-lined channels.
 +
*Check dams may be an obstruction to construction equipment.
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====Permit Applicability====
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Check dams are part of the overall stabilization system for a ditch or channel, and their use is driven by site conditions – specifically, channel slope, length, soil type, and flow velocities. Section IV.B.4 of the 2013 MPCA Construction Stormwater General Permit states that the permittee(s) “must stabilize the normal wetted perimeter of any temporary or permanent drainage ditch or swale that drains water from any portion of the construction site, or diverts water around the site, within 200 lineal feet from the property edge, or from the point of discharge into any surface water. Stabilization of the last 200 lineal feet must be completed within 24 hours after connecting to a surface water or property edge.”
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In addition, the permittee(s) must “complete stabilization of the remaining portions of any temporary or permanent ditches or swales within 14 calendar days after connecting to a surface water or property edge and construction in that portion of the ditch has temporarily or permanently ceased.” Check dams should be used in conjunction with seed, mulch, blankets, mats, and/or other stabilization measures to help meet these requirements.
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====Effectiveness====
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Check dams are moderately effective in trapping sediment, and highly effective in preventing downcutting in a ditch or channel when used with appropriate rolled erosion control products installed over seed. They generally provide relatively fair-to-good removal of coarse and medium-sized sediment from runoff; however, most fine silt and clay particles will pass through the voids on these structures. Their primary benefit lies in preventing erosion prior to seed germination and growth in vegetated ditches and channels. Table 7 summarizes expected performance for an array of typical water quantity and quality target constituents for check dams.
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[[Expected performance for check dams]]

Revision as of 20:46, 24 October 2016

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Check Dams (Ditch Checks, Ditch Dikes)

Definition

Check dams, also called ditch checks, dikes, wattles, etc., are temporary or permanent linear structures placed perpendicular to concentrated flows such as in drainage ditches, channels, and swales to reduce flow velocities and prevent channel down-cutting. Some sediment trapping may occur during low flows. Check dam materials may include rock, fiber logs (e.g., wattles), triangular sediment dikes, sand bags, and other materials or prefabricated systems. Straw/hay bales and silt fences should not be used for check dam applications, as they are not intended for concentrated flow areas.

Purpose and Function

Check dams are not intended as a replacement for proper ditch/channel stabilization (e.g., erosion blanket or turf mat over seed, use of rip-rap, etc.). Check dams help reduce ditch and channel velocities, prevent erosion, and trap small amounts of sediment by intercepting flow along a ditch or channel. The disruption in flow direction and speed creates low velocity areas on the upgradient side of the check dam, causing deposition of heavier sediment particles and resulting in reduced scour potential (i.e., lateral and vertical erosion). Under low-flow conditions, water ponds behind the structure and then slowly drains through, infiltrates, or evaporates. Under high-flow conditions, water flows over and/or through the structure. The main function of a check dam is to decrease velocity, not to collect sediment, although sediment capture and increased infiltration is an added benefit. Check dams are not a suitable substitute for major perimeter sediment trapping measures, and can be easily washed away by high ditch/channel flows if they are not designed or installed properly.

Applicability

Check dams may be used in ditches or channels to reduce erosion and trap sediment. Check dams are relatively inexpensive and easy to install. They are not approved for use in regulated waterbodies (i.e., Waters-of-the-State) without permit coverage from the U.S. Army Corps of Engineers under Section 404 of the Clean Water Act. MPCA water quality certification requirements also apply.

Site Applicability

Check dams are used to regulate flow velocities, reduce scour erosion, and trap small quantities of sediment along higher-risk ditches and channels that have slopes greater than 10 percent and soil types conducive to erosion (i.e., sandy/silty soils). They are appropriate for both temporary and permanent ditches and swales. While most flatter and shorter channels (i.e., slope < 3%, length < 200 feet) generally do not need check dams if they are stabilized immediately after construction (i.e., with sod, or seed and the appropriate rolled erosion control product), longer and steeper ditches can benefit from check dam installations. When evaluating the use of check dams for a particular site, consider the following:

  • When carefully located and constructed, check dams may function as permanent installations.
  • Rock from a temporary check dam can be spread into a ditch and used as a channel lining when the check dam is no longer necessary.
  • Removal may be costly for some types of check dams.
  • Check dams are suitable only for a limited drainage area (generally 10 acres or less).
  • Check dams are intended for use in small open channels, not streams or rivers.
  • Hydraulic capacity of the channel can be reduced when check dams are in place.
  • Check dams may create turbulence downstream, causing erosion of the channel banks.
  • Ponded water may kill grass in grass-lined channels.
  • Check dams may be an obstruction to construction equipment.

Permit Applicability

Check dams are part of the overall stabilization system for a ditch or channel, and their use is driven by site conditions – specifically, channel slope, length, soil type, and flow velocities. Section IV.B.4 of the 2013 MPCA Construction Stormwater General Permit states that the permittee(s) “must stabilize the normal wetted perimeter of any temporary or permanent drainage ditch or swale that drains water from any portion of the construction site, or diverts water around the site, within 200 lineal feet from the property edge, or from the point of discharge into any surface water. Stabilization of the last 200 lineal feet must be completed within 24 hours after connecting to a surface water or property edge.”

In addition, the permittee(s) must “complete stabilization of the remaining portions of any temporary or permanent ditches or swales within 14 calendar days after connecting to a surface water or property edge and construction in that portion of the ditch has temporarily or permanently ceased.” Check dams should be used in conjunction with seed, mulch, blankets, mats, and/or other stabilization measures to help meet these requirements.

Effectiveness

Check dams are moderately effective in trapping sediment, and highly effective in preventing downcutting in a ditch or channel when used with appropriate rolled erosion control products installed over seed. They generally provide relatively fair-to-good removal of coarse and medium-sized sediment from runoff; however, most fine silt and clay particles will pass through the voids on these structures. Their primary benefit lies in preventing erosion prior to seed germination and growth in vegetated ditches and channels. Table 7 summarizes expected performance for an array of typical water quantity and quality target constituents for check dams.

Expected performance for check dams