| Summary: | The Expanded Small-Scale Physical Model (ESSPM) is a distorted-scale, moveable bed model that will complement numerical and field studies studying management strategies in the lower ~140 miles of the Mississippi River and their effect on flooding, navigation and coastal restoration. It is recognized that relative sea level rise (RSLR), the combination of eustatic sea level rise (ESLR) and subsidence, will have an impact on the hydraulics and sediment transport in the lower River. However, it is physically impossible to replicate subsidence in the ESSPM; thus, future RSLR conditions will be experimentally simulated by raising Gulf of Mexico (GoM) levels commensurate to future RSLR. The purpose of this thesis is to develop 1- and 2-D numerical models to quantitatively compare the hydraulics and sediment transport characteristics at both the ESSPM and prototype scales under future RSLR conditions in two ways: (1) the natural conditions where river bathymetry is subsided and GoM levels are raised independently; and (2) ESSPM conditions where the combined effect is modeled as ESLR.
HEC-RAS 5.0.3 was used to develop 1-D prototype and distorted models, as well as a 2-D prototype model. The 1-D prototype model was first calibrated and validated for 2009 and 2010 Mississippi River conditions. The prototype geometry was replicated at the ESSPM distortion (i.e. the vertical and horizontal axes were scaled 1:400 and 1:6000, respectively). A grid was created from the 1-D cross sections to create the 2-D prototype model. Five future subsidence and ESLR scenarios were simulated for each model under RSLR and model conditions (ESSPM SLR) to compare depth, bed shear stress, and velocity. Differences of depth between RSLR and ESSPM SLR decrease with each station approaching the downstream boundary condition of equal depths with maximum RMSE percentages still below 3%. Velocity and bed shear stress are roughly the same between RSLR and ESSPM SLR and start to deviate at Empire (RM 29.5) and Venice (RM 10.7) with significant differences. ESSPM SLR has a smaller impact on ESSPM model compared to prototype model, and differences in both models increase with each scenario. The 2-D prototype model estimates insignificant differences in all parameters compared to 1-D models.
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