Investigating Fluvial Sediment Supply to Coastal Beach-Dune Systems, Humboldt Bay, California

Abstract

Coastal communities around the world are under increasing pressure because of sea level rise, storm surges, coastal flooding, and anthropogenic climate change. Humboldt County, California, experiences the fastest rates of sea level rise in the state, estimated between ~2.53–5.84mm yr-1. Coastal foredunes are frontline defenders of these communities, however, erosion and invasive vegetation threaten their ability to protect inland communities. Rivers are vitally important to beach-dune systems as sediment delivered to the nearshore contributes to accretion and nutrient supply. Three rivers, the Little, Mad, and Eel, are considered, but previous work has established that the Eel River has significantly higher sediment discharge rates (>3x) to the nearshore annually. This project used 73 cross-shore profiles, monitored biannually from 2016-20, extending from the beach to some distance inland of the foredune crest. Volumetric change within the beach-dune system was compared to discharge rates and distance from transects to the nearest river mouth to examine the potential impacts the rivers may have on accretion and erosion rates across the system. Understanding the relationship between sediment input and beach-dune response is crucial to informing coastal communities of potential resiliency-related concerns across the Humboldt Bay region.