Estuaries, where freshwater meets saltwater, are critical ecological and economic zones. Transportation, commerce, and industry have developed in such zones, but these low-lying areas are vulnerable to flooding due to high tides, storms, and river flow. Sea level rise and climate change are increasing the severity of these weather events, highlighting the need for intervention. Adaptation measures help protect critical estuarine regions and their economic assets, and strategies include structural measures such as levees, flood walls, and floodgates, as well as soft measures such as tidal wetland restoration and living shorelines. New research from Kees Nederhoff, Rohin Saleh, Patrick L. Barnard, and Mark Stacey focuses on the San Francisco Estuary, where historical landfilling and shoreline modifications have increased flood risks by reducing natural flood buffers.
Their study, "Mitigating Flood Risks in Urban Estuaries: Tidal Dynamics, Shoreline Hardening, Nature-Based Solutions, and Floodgates in San Francisco Bay," builds on previous works to better understand the balance between hard and soft adaptation measures for urbanized estuaries across the world. Hard adaptation methods, such as shoreline armoring, have been shown to increase tidal levels and damage the ecosystem, whereas soft solutions have shown promise in reducing flood damage and slowing floodwater. This study emphasizes the need for a balanced approach to adaptation that will address the complex and interlinked drivers of flooding in urban estuaries. Learn more about this research in the Journal of Waterway, Port, Coastal, and Ocean Engineering at https://ascelibrary.org/doi/10.1061/JWPED5.WWENG-2342. The abstract is below.
Abstract
Hydrodynamic models are valuable tools for understanding the primary factors influencing daily and peak water levels and for guiding discussions on potential adaptation strategies for managing flood risk in coastal areas. This analysis uses the Delft3D San Francisco Bay-Delta Community Model to simulate water levels and incorporates the effects of a number of adaptation measures in the urban San Francisco Bay estuary, California. In particular, we examine the influence of shoreline hardening, nature-based solutions, and subregional floodgates on regional water levels. The result shows that under present conditions, tidal amplification is responsible for generating a wide distribution of extreme water levels across San Francisco Bay. Tidal amplification is found to decrease under sea level rise, thereby producing a relative damping effect on extremes. A comparison of different shoreline scenarios demonstrates that hard frontal shorelines result in higher tidal amplification, whereas restored (soft) shorelines lower amplification. The current shoreline configuration has both hard and soft characteristics and results in an intermediate tidal response. In some areas, wetland restoration reduces extreme water levels by as much as 20 cm, whereas hard-shoreline addition elevates them by as much as 10 cm for 1.5 m of sea level rise. Furthermore, local floodgates can significantly reduce high water levels without major adverse effects elsewhere in San Francisco Bay. These findings point toward the justification for a range of adaptive measures across political boundaries, weighing hard and soft options in addressing the mounting danger of sea level rise.
Consider the San Francisco Bay scenario for addressing flooding in your estuary in the ASCE Library: https://ascelibrary.org/doi/10.1061/JWPED5.WWENG-2342.
