Semester of Graduation
Master of Science (MS)
Civil and Environmental Engineering
A 2D HEC-RAS model was created to demonstrate applications of hydraulic modeling for informing ecological design. This was done by comparing the hydrologic conditions of a baseline year (2010) to that of the environmental flow prescription from Kozak et al. (2016). The inundation results are relevant to hydraulic connectivity and cypress regeneration.
The hydraulic model was created by assimilating numerous data sources, refining the model with vertical feature (VF) extraction, and calibrating/validating the model. Several topo-bathymetric sources were combined to create the digital elevation model (DEM). Most importantly, this included bathymetry of the backswamp. Polylines of significant VFs in the DEM, such as natural levees, were provided by Dr. Gao. Cell faces of the HEC-RAS mesh (where flow is calculated) were aligned with the VFs. Calibration of a low flow and high flow period was conducted so the model could replicate the hydrodynamics at all times of the year. The model was validated using the 2010 hydrograph.
Different VF and cell mesh sizes were simulated to explore the influence on this model’s performance. The VF and cell mesh sizes were 30 m and 9 m and located in a refinement region. No significant difference in model accuracy or inundation extent was found between the different VF and mesh sizes.
The hydrologic results of 2010 were compared to the prescribed flow results. The area that was inundated in the spring and then experienced 100 or more consecutive dry days in the growing season is assumed to be the most suitable for cypress regeneration. In 2010 that area was 31.0 km2, or 6.7% of the study area. The prescribed flow for an average year increased this to 100.8 km2 (21.9%). If an extreme low flow event were to occur, that would increase the area to 283.8 km2.
Simulation results for 2010 that are similar to Kozak et al. (2016) flow-ecology targets (flows that produce expected ecological services) were extracted. It was found that overbank flooding of the Gulf Intracoastal Waterway occurred during the Overbank Flooding and Backswamp Flooding flow-ecology targets. Widespread overbank flooding did not occur along the Atchafalaya River main channel.
Anderson, Colin, "Using 2D HEC-RAS Modeling with Vertical Feature Extraction to Inform Ecological Design in the Lower Atchafalaya River Basin, Louisiana" (2022). LSU Master's Theses. 5655.