Development of a flow dependent inundation model for evaluating gar (Lepisosteiformes) habitat suitability in the lower Guadalupe River, USA (#226)
This study used a high-resolution, hydrodynamic flood model to develop spatially-explicit flood inundation maps of the lower Guadalupe River that were used to assess habitat and resource availability for a variety of flood dependent species including the alligator gar (Atractosteus spatula). To accomplish the flood inundation modeling we used the USACE 1D HEC-RAS/HEC-GeoRAS model and the 2D hydrodynamic TUFLOW model. The HEC-RAS model was used to estimate the static, 1D flood inundation extents and depths. TUFLOW was used to model flood inundation extents and depths, but was especially useful because of its ability to simulate wetting and drying processes that occur during and after the flood event. Because of constraints with 2D model run-times, we first modeled the entire study area using HEC-RAS, and then used TUFLOW to model a subset of river-floodplain segments identified as having higher habitat suitability. Developing both models required four primary inputs: digital elevation data, discharge and stage data, flow resistance parameters, and boundary conditions that relate the terrain and flow data. The Digital Terrain Model (DTM) of the river and floodplain were developed from LiDAR derived DEMS and additional elevation data. Hydrologic inputs included discharge and stage data. Flow resistance factors were derived from Manning’s n coefficients, and model boundary conditions were determined from DTM and stage-discharge rating curves. Supplementary hydrologic and geomorphic data for model calibration, verification, and validation were collected in the field. Model results were compared to historical cohort strength estimated from otoliths and population monitoring of gar.