Best Management Practices for
Flow Alteration

There are numerous site-specific BMPs for Flow Alteration depending on the watershed and the local area you are working in. In general, flow alteration usually means that streams and bayous have been made to flow faster. Flowing faster means that storm water will be released to the watershed faster causing flooding and NPS pollution downstream.

WHY DO WE CARE? BECAUSE WE ALL LIVE DOWNSTREAM!

Here are a few of these BMPs for watershed level and flow restoration:

  • Control water on site in during construction and development – construction and development usually mean that there is a lot of pavement and rooftops built. These are called impermeable surfaces because water doesn’t permeate it or get absorbed, it just moves off of it. Once a watershed has more than about 15 percent of its area in impermeable surfaces, waterbodies start to become more polluted. If water is controlled on site of a development or during construction, some of the pollution can be prevented. Retention ponds are one way to do this. These are ponds (stormwater detention ponds) that collect the water from parking lots and developed areas. For developments (places where subdivisions are built), sometimes a pond is dug, then the soil dug out of the pond is used to build foundations for the houses that are being built. See the page for Best Management Practices for Urban Runoff.

  • Stream bank restoration/replanting stream banks – One of the most direct ways flow is altered is through the removal of vegetation (trees and wetland plants) along stream banks. One way to help restore the watershed is to plant wetland plants (Louisiana irises, buttonbush, etc.) and trees (cypress, water oak, live oak, etc.) along stream banks that have been cleared. Vegetation helps to stabilize stream banks and stop erosion. It also helps to release water into the watershed slowly. Sometimes it is necessary to re-grade the stream banks before planting anything, but this is very expensive.

  • Cut channels in spoil banks – When bayous and waterways are dredged, the soil that is removed from the bottoms is made into spoil-banks. Spoil-banks act like large levees that block water movement between wetlands and bayous. Water moving in and out of the wetlands helps to carry away chemicals naturally produced in the soil that are toxic to the plants. Cutting channels in spoil-banks help to restore some of the natural flow of water.

  • Replant wetlands – Wetlands help to do a number of things. They remove nutrients, metals, sediments, and restore groundwater. In addition, they also release water slowly to streams and bayous after they have purified the water. Wetlands act as a sponge. If you start adding water to a dry sponge it will begin to absorb the water and will begin to release water only after it is saturated. Wetlands are similar. The will hold water during floods up to a certain point, then release the water gradually. Replanting of wetlands helps to restore the natural function of the watershed by reducing the impact of pollutants flowing to bayous and streams and by decreasing the amount of water flowing into streams at once during storms.

  • Replace stream meanders – This is when you go to streams that have been straightened and you put the natural zig-zag pattern back into the stream. It may sound silly but it has become necessary in some areas where all of the stream habitat has been cleared away and the stream has been straightened. Meanders provide more habitat for fish and aquatic insects (fish food) and it slows down the release of water during storms to the watershed.
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