Terraced/Natural Channel Design
Potential permits required: CWA 404, Threatened & Endangered Species, NHPA, Floodplain
OUTSIDE HELP:
A terraced/natural channel design creates terraces, or benches, between the stream and higher areas such as uplands. This opens the channel, reducing velocities by allowing flood flows to spread out. They provide:
• Channel stability
• Decreased velocity
• Riparian habitat
• Bank stability
Terraced/natural channel designs do not make sense in every situation. There are certainly areas where space is limited and you will not be able to create a series of terraced benches between the stream and more usable spaces where you may have a building. However, there are also many situations where a terraced/natural channel design is possible and will have a lot of beneficial effects.
By creating these terraced riparian benches, you can create benefits for the floodplain, the stream’s flows, the vegetation and the wildlife in the area. The lower benches are meant to flood regularly, providing water to valuable riparian plants. The higher benches should flood less regularly and will have plants that can survive with less watering.
Allowing flood waters to spread out across these benches reduces the speed of the flood flows, also reducing damage flows do to downstream properties.
Re-shaping your streambanks into a terraced design requires careful engineering and planning to figure out the correct elevations for the benches, as well as the correct plant species for each bench. It also requires engineering to calculate the impacts to the floodplain and floodway. The actual construction will involve working in the stream and will require permits as a result.
Example of a Typical Terraced/Natural Channel Design
Before hiring outside help, consider if your property has enough space to create terraces along your streambanks. These terraces can vary greatly in width and they can be on one or both sides of the stream. Looking at nearby streambanks that have terraced benches will help you form an idea of hat could be built on your property.