We took advantage of the extreme water level conditions present during the 2015-2016 El Niño (large water levels and waves) to investigate the response of low-inflow estuarine lagoons to extreme events. This work was supported by a 2015 USC Sea Grant funded project with PIs Giddings and Pawlak: Low Inflow Estuarine Response to Extreme Events: El Niño as an Indicator of Future Conditions in Urban Southern California EstuariesFormer graduate student Madeleine Harvey collected the measurements and used this work as the basis of her PhD dissertation. Specifically, we examined the physical response to extreme water levels (tides, waves) and runoff as these provide windows into future climate conditions. Extreme water level events in these estuaries can significantly impact the morphology, i.e., the shape of the lagoon, by moving large amounts of sediment and thus moving channels and banks, and even altering the height of the bed. Lagoon mouths can completely close, disconnecting them from the ocean, in response to import of sand from the beach and growth of a sill at the estuary mouth. When lagoons shut off from the ocean, circulation drastically changes and slows. This can lead to prolonged periods of hypoxia, or low oxygen conditions. This feedback between hydrodynamics (circulation) and morphology (shape) forms the basis of the processes we are continuing to try to better understand. Please see the USC Sea Grant site for a project summary.

A California Sea Grant Rapid Response project led by Dr. Eric Stein at SCCWRP allowed us to extend this analysis to compare across a wider range of estuaries: Hydrologic and Geomorphic Changes to Southern California Estuaries and Lagoons during Episodic Events Associated with the 2015-2016 El Niño: Insight to Potential Future Response to Sea Level Rise.

A 2020 paper in Estuaries & Coasts by Dr. Maddie Harvey summarizes the “Effects of Elevated Sea Levels and Waves on Southern California Estuaries During the 2015–2016 El Niño.” Important results of this paper highlight the different response of intermittently closed estuaries relative to perennially open estuaries. Intermittently closed estuaries experienced enhanced higher-high water levels during large wave events, and tides were truncated during low tide due to a sill at the estuary mouth. The overall number and length of closures were increased during the 2015–2016 El Niño relative to a typical year.

A 2018 paper in Journal of Geophysical Research – Earth Surface by Dr. Adam Young summarizes the Southern California Coastal Response to the 2015–2016 El Niño, highlighting the different responses of estuaries, beaches, and cliffs. Although some areas experienced significant change, the potential for coastal erosion and damage in Southern California was reduced compared to the 1997–1998 El Niño, because of low rainfall, a northerly swell approach sheltering the region, and relatively limited total high-water levels. In particular the low rainfall was important for minimal cliff retreat but enhanced estuarine response.