The San Francisco Bay Delta Model

The Bay Delta Model

Bathymetry

The bathymetry was derived from historic measured data. These are available here.

Structure operations

The Delta includes a number of operational structures which may be operated in the Bay-Delta model as well. These include (reference to operation data between brackets):

Calibration

Hydrodynamic calibration

Hydrodynamic calibration was carried out for 3 month high river flow conditions (December 16, 1999 until March 16, 2000) and a 3 month period of low river flow conditions (July 16, 2001 until October 16, 2001). All presented data is with respect to NAVD88 (vertical datum), UTM 10 (horizontal datum) and GMT (time reference).

Boundary conditions

Hourly measured water levels at Point Reyes (tidesandcurrents.noaa.gov/) were used as seaward boundary condition. Landward boundary conditions for the Sacramento River were obtained from daily measured river flow data at Freeport (FPT) and for the San Joaquin River near Vernalis (VNS) (cdec.water.ca.gov/). The inflow from the Yolo Bypass was approximated by (Derived after curve fitting data relationship between Qyolo and Qrsac. )

Measured data for the Bay area were derived from tidesandcurrents.noaa.gov/, for part of the Delta from the California Data Exchange Centre cdec.water.ca.gov/ and for station with numbers from direct contact with the Department of Water Resources (DWR).

Calibration was carried out by systematically varying the value of the Manning's coefficient for different sub-areas of the Bay-Delta system. The calibration data analysis includes (local and time varying) influence of air pressure and wind in the definition of the boundary condition as well as in the calibration data inside the modeling domain. These may account for (part of) the error between measurements and modeling results. Also, the NAVD88 reference is not known for all measurement stations, although tidal water fluctuations may be modeled properly. To circumvent these distortions a better method to assess the model performance is to focus on water level amplitude and phasing of the different tidal constituents. Boundary conditions, calibration data and model results are thus decomposed by Fourier transformation into tidal components which are then compared. The following table gives the results of this analysis for 34 tidal constituents at Golden Gate (GGT) for high river flow conditions. By far, the main tidal constituents at (GGT) are O1, K1, N2, M2 and S2, with M2 being the largest. The model represents their values quite well. The difference in amplitude is 1.3 % for M2, up to 14% for O1, but the phasing shows a maximum of only 3% (O1)).

Calibration results in figures

The following tables give calibration results for the high and low river flow conditions (NaN means that measured data were not fully available during the modeled time period). The largest (extreme) deviations are explained by the fact that the measured water levels did not have a known reference to NAVD88. 

Visualization of the figures