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Mitigation Bank Coverage

Iowa Stream Credits

Stream Mitigation

In recent years, as new information has come to light concerning the immediate, secondary, long-term, and cumulative adverse impacts associated with stream channelizations within our Regulatory District, we have adapted a more rigorous review of stream channelization applications.  Channelizations tend to (among other things) increase sediment loads and turbidity, as well as downstream bed and bank erosion, sedimentation, and flooding; cause upstream down cutting, lower groundwater tables, reduce or adversely impact fish and wildlife habitat, drain wetlands, and warm water.  Channel straightening projects also can threaten bridges (and other infrastructure) upstream and downstream due to the potential for downstream erosion and upstream down cutting as the channel works to re-establish its previous slope.  Projects can significantly reduce the existing channel length, while greatly increasing the channel slope, maximizing the adverse effects described above.  Less damaging (to the aquatic resource) alternatives should be considered.  Those alternatives may include armoring the affected stream banks within the project area with quarry rock or broken concrete riprap to abate further channel movement, the excavation of accumulated sediments from the existing channel (without altering the existing alignment), the cutting back of the channel banks to establish more stabile side-slopes, and the establishment of vegetative buffers along the creek.  Generally, there are minimal concerns over the use of conventional bank stabilization methods, such as the placement of riprap and/or bio-engineering techniques and buffer establishment, and the cleaning out of sediments and debris from the existing channel (provided all excavated material is placed in an upland, non-wetland location).

In general, foot-for-foot stream length replacement will be required as mitigation for stream impacts.  The below stream mitigation methods are tools that can be used to determine necessary stream mitigation.  The Corps of Engineers will make a final determination as to the adequacy of stream mitigation.