Drivers of Morphodynamic Change and Hypoxic Events in Southern California Lagoons

Research > Current Projects > Drivers of Morphodynamic Change and Hypoxic Events in Southern California Lagoons

 

Sarah N Giddings, Assistant Professor, University of California, San Diego, Scripps Institution of Oceanography

Geno Pawlak, Associate Professor, University of California, San Diego, Dept. of Mechanical and Aerospace Engineering

Project Funding: 2016-2018

Project Overview:

Low inflow estuaries, prevalent throughout Southern California, provide extensive ecological and human benefits. The number and total area of these systems have been drastically reduced and those systems that remain are heavily modified by human development. It is unclear if these estuaries can maintain their roles as key contributors to habitat, biodiversity, carbon storage, and coastal protection. The response and resiliency of these systems to elevated water level events are particularly poorly understood. Some work has shown that extreme events have the ability to drastically modify morphology and transition vegetation structure, yet the physics underlying these processes has not been studied in detail. Thus we aim to explore in detail the coupled hydrodynamic-sediment transport mechanisms and their impact on larger scale system morphodynamics and hydrodynamics in urbanized Southern California estuaries in order to inform sustainable development and future adaptation.

Our project objectives are to:

• Assess the impact of wave-current interactions on sediment transport and the morphodynamic responses to extreme events in Southern California LIEs using in-situ and remote observations

• Compare results from two different types of LIEs (marsh vs. embayment)

• Use these observations to make predictions about the response of these estuaries to future conditions including sea level rise and elevated water level events in order to assist managers in planning dredging events and in adopting coastal resiliency programs

We plan to approach these broad objectives by asking the following research questions:

• What is the relative importance of waves, wave-current interactions, and mean currents in driving sediment transport in estuarine mouths?

• How does hydraulic control at an estuarine mouth regulate wave-current interactions and thus sediment transport and hypoxia (through reduced flushing) on tidal and event time scales?

• How will an embayment respond relative to an intertidal marsh-like system?
  
  

Read the summary project proposal

Return to Current Projects

• 2018 Progress Update: 
  
  

  Results assess the impact of extreme storm and wave events in different types of Southern California estuaries. The study has maintained long term measurements of water level, current velocity, stratification, dissolved oxygen, stream flow, waves, and drone footage, and researchers have drafted a paper comparing results from multiple estuaries. Analysis so far suggests that estuaries that have structures (jetties, groins, etc.) tended to remain open and experience less sediment accretion and less exacerbated high water levels than estuaries without structures (which also tend to have more marsh habitat). However, structures enhanced erosion of the adjacent beaches. Analysis also shows that a single storm event lasting 1-2 days can result in large-scale sediment changes and alter lagoon circulation for weeks. Further analysis and collaboration with coastal mangers will occur in the final year of this study and will help managers better predict the response of estuaries to climate change impacts and adopt coastal resiliency programs to reduce damage in the future.

• 2017 Progress Update:
  
  Analysis is underway. Our intensive measurements during the winter 2015-2016 El Niño season clearly document the importance of both wave-current interactions and morphology (sill height) on sediment transport during high water level events. In particular we find that infragravity waves dominate incoming wave energy in the lagoon and are modulated by the water height relative to the sill and the strength of the currents at the mouth. When water levels are above the sill and the tide is flowing into the estuary, infragravity waves can propagate significantly far into the inlet and move sediment. This is an important contribution to the field as it narrows in the physical processes that can drive sediment transport and thus morphodynamic responses in these types of estuaries. The goal of making predictions about the response of these estuaries to future conditions is ongoing.

• Project photos courtesy of Sarah Giddings Lab
  
  Los Peñasquitos Lagoon -