Isleta Diversion Dam Effects of Fishway Length and Width on Flow Hydraulics and Orientation: 2D Hydraulic Modeling

The Isleta Diversion Dam (IDD) spans a reach of the Rio Grande located approximately 10 miles south of Albuquerque, New Mexico. The Middle Rio Grande Conservancy District (MRGCD) built the dam in 1934, while the US Bureau of Reclamation (Reclamation) rehabilitated the dam in 1954. Presently, additional modifications are planned for the dam’s east sluiceway as well as to add fish passage capabilities. While the sluiceway modifications aim to improve sediment management in the irrigation canals to which IDD diverts water, the fish passage modifications target the Rio Grande Silvery Minnow (Hybognathus amarus, hereafter RGSM). This fishway will provide opportunity for upstream dispersive passage of the RGSM during the irrigation season. During periods of high flow that occur during spring runoff, sediment deposition is very likely to occur around the fishway. Sediment transport and deposition alongside and downstream of the fishway is influenced by gate operations. Reclamation’s Sedimentation and River Hydraulics Group two-dimensional numerical model (SRH-2D) was used to evaluate various fishway length and width designs to determine optimum length, width, configuration, and orientation that will equalize sediment deposition and transport along each side of the fish passage structure and identify gate operations that will likely reduce or eliminate the need for mechanical sediment removal. The recommended fishway length, width, configuration, and orientation for future design is presented.