Research - Category I: Hydrology, Climatology & Hydraulics

Hydrodynamics of Shallow Water Habitats in the Sacramento-San Joaquin Delta
(Funded 2000-2001)

Principal Investigator: Mark Stacey
Department of Civil and Environmental Engineering
UC Berkeley
(510) 642-6776
mstacey@socrates.berkeley.edu

Executive Summary:
We propose to carry out a combination of field data analysis and numerical modeling to examine the hydrodynamics of shallow tracts of open water in the Sacramento-San Joaquin Delta ("delta lakes"). The Delta is critically important to California water, as it is a source of drinking water for a large fraction of the state's population. At the same time, the Delta also provides water for agricultural uses and a valuable ecosystem which may be irreplaceable. The complexity of the system makes its management difficult, as every alteration which improves its function for one objective has implications in other areas.

In the CALFED process, a great deal of attention is being paid to the protection and renovation of the Delta ecosystem, which was fundamentally altered a century ago as the marshlands of the Delta were "reclaimed" for agricultural use. It is important, therefore, to understand the role that the delta lakes currently play in the Delta ecosystem. Eventually, we expect this area of research to expand into an interdisciplinary study of the shallow water ecosystems, including the transport and dispersion of sediment, contaminants and biota. Any such study, however, must incorporate an understanding of the hydrodynamics of the system which will drive the transport and dispersion of other constituents.

The hydrodynamics of the delta lakes are forced by tides propagating upstream from the San Francisco Estuary, wind and Freshwater flow, but will also be influenced by variations in depth, bottom roughness, and vegetation. All three forcing mechanisms have well-defined timescales associated with them, which defines the timescales over which we will examine the system. These timescales range from ours (tides and wind) to days (freshwater runoff) to weeks (tides, spring-neap cycle) to months (seasonal nature of freshwater runoff). It is important to understand asymmetries in the tidal flows at all of these timescales, as asymmetries can have large impacts on the net transport of scalars, such as sediment.

The study described in this proposal is designed to observe and model the details of the hydrodynamics which govern the physical transport and dispersion of sediment, biota, contaminants and nutrients in three delta lakes: Sherman Lake, Franks Tract, and Mildred Island. This choice of study locations spans a range of conditions: with variations in the strength of the tidal forcing, depth, and level of vegetation. The first phase of the project will involve the analysis of existing data sets which have been collected by the USGS, with a small amount of supplemental data collection. This analysis will be targeted towards identifying temporal asymmetries in the flows at the timescales identified above, as well as spatial variability within the delta lakes which may be influenced by geometry or vegetation.

Following this analysis of the data from Sherman Lake, we will collect some data from the other bodies of water, particularly Mildred Island. The data collection will consist of velocity measurements at the openings to the delta lake to define transport across the interface. Additionally, measurements will be made through the interior of the lake to define circulation for a variety of tidal, freshwater, and wind conditions. The measurements will be made with instrumentation to be provided by the P.I. from a whaler, for which funds are requested. At the same time, we will begin to develop a hydrodynamic model for use in these shallow bodies of water. The model will be an application of the free-surface model, TRIM, which has previously been applied to other parts of the San Francisco Bay-Delta system (Casulli and Cheng 1992).

Support for this project is requested in the form of graduate student support for two years and salary support for the P.I. for 1/2 month each summer. The graduate student will take the lead on the analysis of the data sets and on the application of the hydrodynamic model to the lakes under consideration. Additionally, funds are requested to facilitate some preliminary surveys of the study sites, including the use of a whaler owned by the Department of Geography at UC Berkeley (available at a rate of $50/day).

The goal of the project described here is the development of tools which will provide a foundation for more detailed studies of the dynamics of these shallow water ecosystems. These studies are likely to be interdisciplinary, and we expect to collaborate with other scientists working in the field, including individuals from the USGS. The Delta ecosystem is an important consideration in the management of this critical California water resource. This is an area of great interest to the P.I. and it is expected to be a long-term area of research.