Constructed Pools-and-Riffles: Application and Assessment in Illinois.

The diversity of Illinois' streams provides a broad range of conditions, and thus a variety of restoration techniques may be required to adequately compensate for watershed alterations. Resource management agencies and research institutions in the state have collaborated on a variety of applied research initiatives to assess the efficacy of various stream protection and restoration techniques. Constructed pool-and-riffle structures have received significant attention because they tend to address watershed processes (i.e., channel evolution model) and may benefit biotic communities and processes along with physical habitat. Constructed pools-and-riffles have been applied primarily to address geomorphic instability, yet understanding biological responses can provide further rationale for their use and design specifications. In three stream systems around the state, fish were collected pre- and post- installation of structures, using primarily electrofishing techniques (e.g., electric seine & backpack). In general, within the first five years after installation, changes in fish communities have included a shift from high-abundance, small cyprinid-dominated assemblages to low-density Centrarchidae and Catostomidae assemblages. Changes in macro invertebrates at selected sites included increases in filter feeders and sensitive taxa such as the Ephemeroptera, Plecoptera, and Trichoptera (EPT). Ongoing assessments will be critical for understanding long-term influences on stream ecosystem structure and function.