A study of sub-tidal transport in Suisun Bay and the Sacramento -San Joaquin Delta, California.

摘要

Scalar transport and mixing on tidal, tidally-averaged, spring-neap, and month-long timescales in Suisun Bay and the Sacramento-San Joaquin Delta was studied using a numerical modeling approach. TRIM3D (Tidal Residual Intertidal Mudflat Model), a three-dimensional hydrodynamic and scalar transport model developed by Casulli and Cattani (1994) and Gross (1999) was modified, calibrated and verified for this application. The model was used in both two-dimensional depth-averaged and three-dimensional applications.;Comparison of model results with field studies both for salt and dye releases on a tidal timescale showed that the model represents scalar transport well. The model can also calculate X2, a key regulatory parameter that predicts salt intrusion for this system.;The tidally-averaged transport analysis showed that mean flows control water transport, but that mean advective flux does not control scalar transport in the entire Delta. Dispersive flux or mean advective flux can be the primary scalar transport mechanism depending on the location and the amount of inflow to the system.;The interaction of wave transport, tidal stress, friction, and the barotropic pressure gradient are the important forces that cause the filling and emptying of the Delta. In addition, the physical connection between the Sacramento and the San Joaquin by Three Mile Slough keeps the Sacramento and San Joaquin in equilibrium in the Western Delta.;The long-term transport study showed that the location of temporary barriers, gate operations, and flow through the Yolo Bypass all contribute to the circulation patterns and source fractioning of water in the Delta. Source fractions of Sacramento, San Joaquin, agricultural drainage, and Yolo Bypass water in a water column can be predicted at locations throughout the Delta using Delta TRIM3D.;Mixing mechanisms in specific regions of the Delta were also modeled. Using passive scalar (or "numerical dye") releases, mixing in two shallow water habitats within the Delta showed that the location and size of levee breaches, bathymetry, flow in the system, and the influence of tides all control residence time in these systems. The numerical drogue release studies for Three Mile Slough and the confluence region showed that Lagrangian velocities in both regions are a function of the time and the location of the release. Tidal pumping and trapping is an important mixing mechanism in both regions.