Using Bathymetric LiDAR and a 2-D Hydraulic Model to Identify Aquatic River Habitat

The Bureau of Reclamation (Reclamation) is currently studying various alternatives to improve salmonid habitat throughout the Yakima Basin in central Washington. In an effort to accomplish this goal, Reclamation is evaluating the effects of modifying flow releases throughout the year and increasing storage in the basin. A two-dimensional (2-D) hydraulic model has been used to identify various habitat types, including off channel habitat, spawning habitat, and pools, riffles, and glides for a wide range of flow rates. Spawning habitat was identified with Froude values between 0.3 and 0.6 using independently collected spawning data. Off-channel habitat is identified as side channels become active at various flow rates. Pool, riffle, and glide habitats are identified by assigning each habitat type a specific range of the Froude number. The results were verified through field investigations of the modeled reaches. The major component of a 2-D hydraulic model is well-defined stream channel geometry. This type of data can be difficult to obtain, particularly for long study reaches. To resolve this issue, water penetrating airborne LiDAR was used to map approximately 153 river kilometers of bathymetry on the Naches and Yakima Rivers. This data was then combined with terrestrial LiDAR to create a complete surface with which to model hydraulics. The ability of airborne LiDAR bathymetry to map shallow water river environments is in early stages of development. The accuracy and precision of those measurements is summarized.