Available at: https://digitalcommons.calpoly.edu/theses/3161
Date of Award
9-2025
Degree Name
MS in Civil and Environmental Engineering
Department/Program
Civil and Environmental Engineering
College
College of Agriculture, Food, and Environmental Sciences
Advisor
Stefan Talke
Advisor Department
Civil and Environmental Engineering
Advisor College
College of Engineering
Abstract
This thesis examines how tidal backwater effects and riparian restoration influence flooding in the Chorro Creek watershed, a major tributary to the Morro Bay Estuary on California’s Central Coast. Restoration efforts, including levee removal, floodplain reconnection, and revegetation have attempted to improve ecological function and reduce sediment transport. However, recent flood events suggest that these changes may also affect local hydraulics in ways not fully anticipated, particularly under the influence of tides and sea level rise. To analyze these dynamics, a two-dimensional HEC-RAS model was developed using LiDAR terrain, historical imagery, and field data collected from pressure and ultrasonic gauges. The model was calibrated with limited observed storms and verified against separate events, then applied to simulate a range of fluvial and tidal stages under present and future sea levels. A statistical analysis of observed peak stage heights was conducted to evaluate flood behavior during compound events. Comparing model results from the different scenarios indicate that the increased channel roughness resulting from restoration resulted in larger simulated water levels during high-creek flow events. Measured tidal backwater effects extend beyond the limits assumed in existing flood maps and significantly alter water levels near key infrastructure such as South Bay Boulevard and State Park Road. Under projected sea level conditions, even moderate storms may produce flooding in previously unaffected areas, especially if they occur in combination with high tidal conditions. This study highlights the importance of integrating tidal dynamics and restoration impacts into hydraulic modeling and floodplain management. It underscores the need for updated design standards, more accurate flood mapping, and adaptive planning strategies in tidally influenced watersheds. By linking hydrodynamic simulation with ecological restoration and tide stage effects, the research offers a framework for managing flood risk and environmental resilience in coastal systems.