Development of Design Methods for In-Stream Flow Control Structures

Project summary:

Efforts to stabilize and restore streams and rivers across the nation have grown dramatically in the last fifteen years, with over $1 billion spent every year since 1990. Despite the large investment, it is estimated that at least 50% of stream restoration projects fail. This is due in large part to the fact that complex physical processes govern the interactions of turbulence in the water column with sediments in the stream and the bank. Consequently, stream restoration is today more of an art than a science. This project couples an in-depth review of the current use of in-stream structures with a comprehensive study using physical and numerical models to explore the most promising structures. In addition to performing a comprehensive review of the literature, the combined experience of transportation and natural resource departments is assembled and organized in this project to describe and evaluate existing low-flow structure applications and failure modes. These results support physical investigations at three scales: 1) Small scale (within a three-foot-wide laboratory flume); 2) intermediate scale (within a sinuous channel in the Saint Anthony Falls Laboratory's newly developed Outdoor StreamLab (OSL)); and, 3) field scale. Results obtained within the laboratory and OSL experimental studies are compared to and verified against measurements obtained from existing field installations. Results from these measurements will be extended to a wide range of other stream morphologies using a numerical model, which will provide the breadth of information necessary to develop guidelines for the successful construction of stable in-stream structures in a wide range of streams. These results will be combined into comprehensive quantitative engineering guidelines.