In this regulatory guidance letter, the U.S. ACE determine the removal of obsolete barriers as an “effective approach to restoring river and stream structure, functions, and dynamics.” They agree that barriers can negatively alter a stream’s flow, sediment transport, nutrient cycling process, species composition, and upstream and downstream movement of species. And that the removal of these barriers can substantially reverse those impacts, thus, supporting the U.S. Clean Water Act.
For these reasons, district engineers are given mitigation credits if they remove an obsolete barrier. To receive credits, the U.S. ACE give some examples of factors that are important to consider when starting a mitigation project. If the project can/will contribute to the recovery of endangered or threatened species, recovery of migratory fish species, improvements in habitat and water quality, and the distance to the next barrier then district engineers are eligible to receive credits.
“[T]he number of mitigation credits [given] should be based on increases in ecological functions that will be present or are expected to occur when the compensatory mitigation project achieves its objectives.” In other words, these credits can be redeemed only when the expected results are gained.
Hopefully this guidance letter can help to tear down the one to two million obsolete, small barriers in the U.S.! Every step counts towards a free-flowing earth.