Dynamic Solutions

Bay-Delta Sea-Level Rise Model

bd_slrThe USACE Sacramento District tasked DSLLC to develop a hydrodynamic model of San Francisco Bay and the Delta to analyze the effects of sea level rise on water levels and salinity in the Delta. The project included development of low, medium, and high sea level rates of the Pacific Ocean at San Francisco, the development of a subsidence rate for the Delta, and the application of these values for 50 and 100 years in the future to evaluate the potential effects of sea-level rise on natural and managed ecosystems and human systems in the Delta.

The model covers the entire Delta region with the southern boundary defined by the USGS gage located on the San Joaquin River at Vernalis and the northern boundary defined by the USGS gage located on the Sacramento River at Verona and the Yolo Bypass. The western boundary is defined at the Pacific Ocean offshore to the Farallon Islands. Land boundaries were established at the 16 ft contour in order to capture up to that height in sea level rise, as needed in subsequent work. Bathymetric and topographic data were associated to a common datum and combined to create a seamless model grid allowing for progressive inundation at the land-water boundary.

Water levels at the NOAA tide gage at San Francisco, with records dating back to the mid-1800’s, were utilized to determine rates of sea level rise under low, intermediate, and high scenarios. The rates computed were cross-checked with rates reported by the International Panel on Climate Change, California Climate Center, and the California Department of Water Resources. The combination of sea level rise and land subsidence could lead to larger impacts in the Delta. A literature review was performed to ascertain quality subsidence rates for the Delta. An accepted rate for Delta channels does not exist so information from reports on island subsidence and geologic subsidence of the landform were reviewed.

This study provided critical information for USACE planning efforts in the Delta. The changes in water level and salinity forecasted will have enormous impacts both on infrastructure and ecosystem function. Long-term planning efforts require this foresight to design effective strategies for ecosystem restoration, flood damage reduction, and water supply initiatives.

 

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