River training and ecological enhancement potential using in-stream structures

The use of in-stream flow training structures for channel stabilization has become increasingly popular due to its potential cost effectiveness and ecological benefits. When properly designed and maintained, these structures help to protect the channel from erosion and lateral migration and may also provide grade control. Additionally, in-stream structures may improve fish and macroinvertebrate habitat and increase hyporheic exchange. However, a large number of these projects fail due to inadequate design guidelines. In this study, various types of in-stream sill and deflector structures are described. A literature review including case studies, journal articles, and standards developed by various agencies suggests design guidelines which are currently available but do not meet the rigorous engineering-based hydraulic design criteria necessary for success. A practitioner opinion survey of personnel from state agencies, federal agencies, and private firms indicates that these structures are being used extensively in at least 76% of the USGS physiographic provinces. In general, respondents indicated that in the areas of cost, performance, maintenance, and environmental enhancement in-stream structures are preferable to the most common alternative: riprap revetment. Information from 39 case studies suggests that successful projects involve multiple structures and are located in rivers with relatively high aspect ratios.