Potential permits required: CWA 404, Threatened & Endangered Species, Floodplain
A constructed riffle is a grade control and habitat structure built by placing river cobble in a stream to create changes in flows that benefit aquatic organisms. Benefits of installing constructed riffles include:
• ‘Structural’ way to ‘drop’ grade in a stream
• Fish and insect habitat
• Added oxygen to the water
Constructed riffles mimic riffles that occur naturally in stream systems. Often, riffles are part of a ‘sequence’ of in-stream structures. Moving downstream, a riffle will be followed by a pool, then a fairly calm section of stream, then another riffle. You will see this sequence both in constructed stream systems and natural streams.
The design and construction of a constructed riffle involves engineering for structural stability and floodplain impacts. It also requires environmental and wetland considerations. All of these impacts mean that permitting will be required for constructed riffles. While these structures mimic natural features, installation into existing streams requires careful planning to ensure they don’t cause unintended negative effects.
When selecting outside resources for your project, be sure to check references. It is always helpful if the consultants and constructors have experience designing and installing similar projects, especially in your area. Once selected, they should be able to discuss design options, construction costs, timeframe and what the construction process will look like. You can also discuss revegetation options for any areas disturbed by the work with the consultants.