Observations of Wave, Current, and Wave-Current Induced Sediment Transport in the Inlet of a Small, Shallow Estuary

The coupling of the hydrodynamics and morphodynamics in a tidal inlet are examined to understand the relative importance of waves, wave-current interactions, and mean currents in sediment transport processes in a low-inflow estuary. This study uses data collected in Los Peñasquitos Lagoon (LPL) in San Diego, CA from Winter 2014 to Winter 2015. LPL is a small, shallow, low-inflow estuary whose mouth is located in the middle of a long, sandy beach in Southern California. Waves and currents drive sand transport from the beach into the mouth of the lagoon where accreting sand forms a sill that intermittently limits or blocks the lagoon’s exchange with the ocean. The sill modulates the water level in the lagoon through hydraulic control and regulates the amount of wave energy able to propagate into the lagoon due to depth-limited breaking. Infragravity period waves (>30 second) propagate furthest into the lagoon. The offshore wave field, the tidal phase, and the sill height influence the waves and currents in the lagoon and thus influence the wave-induced and wave-current induced bed stress. The bed stress dictates the amount of sand that can be transported into the lagoon through suspension and bed load. Acoustic Doppler velocimeters (ADVs), deployed during large wave and surge events, are used to measure the wave orbital velocities, currents, turbulence, and bed shear. Optical backscatter sensors, deployed alongside the ADVs, are used to quantify the suspended sediment fluxes during the extreme events. A time-lapse camera directed at the mouth and bathymetric surveys are used to quantify the net sediment movement in the lagoon.