Hydrodynamics of shallow water habitats in the Sacramento-San Joaquin Delta
Over the past 3 years, we have pursued extensive research into the hydrodynamics of shallow water habitats in the Sacramento-San Joaquin Delta. The goal of these studies was to evaluate the relative importance of the various physical forcing mechanisms and influences, while developing the research tools required to address the dynamics of the systems. This work has led to larger-scale grants from CALFED and collaborations with the U.S. Geological Survey, which has facilitated extensive research into the hydrodynamics of shallow water habitats through a combination of field observations and numerical modeling.
Data from two sites has allowed us to begin the contrast the dynamics of different shallow water habitats in the Delta. The first site, Mildred Island, is influenced by forcing from the tides, wind and diurnal heating and cooling. The Island as a whole is a low energy environment, but the details of transport throughout the system are exceptionally subtle and complicated. To further evaluate the relative importance of each of these forcing mechanisms, an existing numerical model, TRIM-3d, has been applied to Mildred Island. After modification to allow for heating and cooling, the model has reproduced the primary trends in temperature over the timescales of several weeks. Using this model, we have evaluated residence times under various forcing conditions to conclude that wind and diurnal heating and cooling play an important role in determining the flushing of particular subregions within the Island.
The second site, Franks Tract, is dominated by tidal forcing and the interaction of tidal flows with vegetation, which develops on a seasonal timescale. Emphasis to this point has been on data analysis, and we have defined representative mean velocity profiles and surrogates for exchange between the vegetated and unvegetated regions of the flow. It appears that these exchanges are driven by intermittent flow instabilities which are likely to develop along the interface between vegetated and unvegetated regions of the flow.