We will advance scientific, engineering, and policy perspectives on how sediment can be managed in coastal lowlands to reduce flood risk, bank instability, and erosion risk. We will evaluate sediment management practices for both average and extreme event conditions by investigating how varying tides, stream flow, and precipitation influence sediment, a fundamental feature of coastal lowlands.

Why We Care
The Southern California coastline is characterized by highly developed upland habitat and less developed rocky cliffs, coastal lowlands, estuaries, and beaches pinned between the developed upland and the Pacific Ocean. This coastal lowland region is less than two meters above current high tide levels and includes over 17,000 square miles of estuarine habitat. This region of the country is culturally and economically dependent on the coastline, and contains estuarine habitats that host numerous threatened or endangered species.

What We Are Doing
We will evaluate sediment management scenarios in lowland watersheds of Southern California by developing models specific to the two largest estuarine systems in the region: the Tijuana River Estuary and the Newport Beach Estuary. These systems represent a sediment rich, natural system, and a sediment poor, urban system, respectively.

The models will link scenarios of sediment management with resultant effects on natural infrastructure (e.g., beaches and wetlands), then assess vulnerability of the region to sea level rise and extreme weather events under the scenario. These tools will enable analysis of (1) flood risk, (2) sediment instability and erosion risk, and (3) habitat distribution afforded by alternative sediment management practices.

We will also develop a framework to improve the characterization of extreme events (flood hazards) associated with multiple drivers, such as a combination of storm tides, streamflow, and precipitation. This important modeling challenge facing coastal areas has yet to be systematically addressed, and is a fundamental issue for analyzing and comparing alternative strategies to avoid the inundation of coastal lowlands.

A management advisory team will codevelop models with the lead scientists to ensure that the resultant tools and information have the greatest potential to explain tradeoffs in sediment management approaches in ways that can guide management and policy decisions for coastal lowlands in Southern California. The outcomes of this project will be to improve knowledge and tools for the innovative management of sediment. Our recommendations for sediment management will support regional policy and practice to ensure coastal lowlands can adapt to rising sea levels.

What We’ve Accomplished
The project advanced models that link scenarios of sediment management with resultant effects on natural infrastructure (e.g., beaches and wetlands), and then assessed the vulnerability of the region to sea level rise and extreme weather events under each scenario. The Newport Bay, the Orange County Department of Public Works coordinates regional National Pollutant Discharge Elimination System stormwater and TMDL compliance efforts on behalf of the County, Orange County Flood Control District, and the cities of Orange County. By identifying Newport Bay as a potentially sediment-deficient environment, municipal staff and regulators are revisiting future sediment management planning strategies, which have historically cost more than $200 million dollars over nearly 4 decades for Newport Bay and San Diego Creek related to the Sediment TMDL. These tools are enabling the analysis of flood risk, including compound flooding, sediment instability and erosion risk, and habitat distribution afforded by alternative sediment management practices and beneficial use of dredged sediment, as well as helping others explore opportunities to finance watershed management projects. This project resulted in 10 peer-reviewed publications.

The project is led by the University of California, Irvine and is funded through the Effects of Sea Level Rise Program. Project partners include the University of California, Irvine; and the Southern California Coastal Water Research Project.