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1 S U M M A R Y In-stream flow control structures have been promoted as an alternative to traditional engineering methods employed for protecting rivers and streams against erosion and scour, thus stabilizing them against lateral migration. These structures work in a fundamentally different way that provides a more sustainable solution to the problem of bank erosion. Instead of strengthening the bank to withstand the applied hydrodynamic forces, as rip- rap and similar protection techniques do, they shift the high-velocity thread away from the bank by altering the stream-flow patterns. Furthermore, they typically use less construction material and have the potential for enhancing the availability of stream habitat. Research- ers at St. Anthony Falls Laboratory (SAFL) and Virginia Tech coupled an in-depth review of the current use of in-stream structures with a comprehensive study of five of the most commonly used in-stream structures using physical and numerical experiments. Physical experiments were conducted at two scales, a laboratory-scale straight-channel flume and a field-scale meandering experimental channel. After extensive validation using the physical experimental results, a state-of-the-art coupled hydrodynamic and bed morphodynamic model developed by researchers at SAFL was used to investigate the performance of vari- ous structure configurations under different geomorphic settings. This model, dubbed the Virtual StreamLab (VSL3D), is capable of simulating the complex three-dimensional flows around in-stream structures and their interaction with the streambed. Shallow, low-flow structures can span all (sill structures) or part (single-arm structures) of a stream channel. Single-arm structures (rock vanes, J-hook vanes, and bendway weirs) were evaluated for their ability to provide bank protection, redirect the channel thalweg, and provide scour pool habitat. Sill structures (cross vanes and W-weirs) were evaluated for their ability to provide bank protection, grade control, and scour pool habitat. Failure mechanisms for all structures were evaluated, including structure undermining, rock dis- placement, and flanking (or circumvention behind the structure). Structure configurations were optimized using a systematic approach, first evaluating structure angle, then evaluat- ing spacing and number of structures and location in representative sand and gravel rivers. Results from the review, practitioner survey, field case studies, physical experiments, and numerical investigations were integrated to develop in-stream structure design guidelines. Design Methods for In-Stream Flow Control Structures
