9
Refinement of Carriage Water Routine
Work continued by Delta Modeling staff to refine the carriage water routine
used in DWRSIM's Minimum Delta Outflow (MDO) submodel. To date, a modeling
approach superior to the current routine has not been developed. This chapter
summarizes work that has been conducted over the past year to develop a refined
model.
Statistical Analysis of Data
While under contract with DWR, R. Shumway and R. Azari of the University of
California at Davis used time series analysis techniques to analyze historic
flow and electrical conductivity data collected at several Delta locations (R.H.
Shumway Consulting 1993) . The consultants examined various approaches to
selecting transformations and filters for linearizing flow concentration
dynamics. Using 14day moving averages, sampled weekly, they developed a linear
transfer function model for predicting log proportional changes in concentration
from past log proportional changes in concentrations and flows. It was noted
that model uncertainty increases rapidly as the length of the forecast window
increases. Therefore, the consultants concluded that the model is most
applicable for making one or twoweek forecasts for given increases in flow or
exports.
Transition Matrix Model Proposal
G. Bogle, a consultant for Water Engineering and Modeling, submitted a
proposal to develop a simplified Delta hydrodynamic/water quality model to
replace MDO (Water Engineering 1993). The key idea behind the use of the
"transition matrix" model (TRANSAL) as a carriage water routine is
that it offers the advantages of a more sophisticated numerical model (e.g.
accuracy) along with much greater computational speed. Computational speed can
be attained by saving and reusing simulation results from DWRDSM in matrix form.
Because matrix development and TRANSAL calibration depends on a numerical Delta
model, Delta Modeling staff determined that further consideration of this
approach should be postponed until the FourPoint Model is operational.
CCWD's Antecedent Outflow Model
Delta Modeling staff have studied the Antecedent Outflow (G) model developed
by Contra Costa Water District (Denton 1993). This modeling approach is
being used by staff to develop salinityoutflow relationships for several
western Delta stations. The G model was applied to the analysis of EPA's
proposed X2 standards (DWR 1994). It was observed to be quite sensitive
to the weighting scheme selected to estimate model parameters. A project is
currently being undertaken to compare the abilities of the G model and MDO in
predicting salinity and required outflow to meet salinity standards at Rock
Slough.
TwoStraw Analysis
Delta Modeling staff undertook a study to develop a modified form of MDO
while maintaining the basic net flow/Delta pool logic intact (DWR 1993).
The main modification was to set western Delta salinity equal to Jersey Point
salinity according to a salinityoutflow relationships developed by E. Winkler (DWR
1985). Possible extensions to this modeling approach might be to (1)
incorporate the G model to predict Jersey Point salinity and (2) modify the MDO
logic to incorporate tidal mixing and exchange (Denton and Hunt 1986).
References
Denton, R.A. (1993). "Accounting for Antecedent
Conditions in Seawater Intrusion Modeling  Applications for the San Francisco
BayDelta." Hydraulic Engineering 93, Vol. 1 pp. 448453.
Proceedings of ASCE National Conference on Hydraulic Engineering, San Francisco.
Denton, R.A. and Hunt, J.R. (1986). Currents in San
Francisco Bay: Final Report. Hydraulic and Coastal Engineering, University
of California, Berkeley, March. UCB/HEL86/01.
DWR (1985). Preliminary Development of a Statistical
Approach to Salinity Modeling in the Western SacramentoSan Joaquin Delta and
Suisun Bay. Technical Information Record 1463CD04.
DWR (1993). Developing ExportOutflow Relationships with
"TwoStraw" Approach. internal memorandum from P. Hutton to F.
Chung, July 7.
DWR (1994). CCWD's Antecedent Outflow Model: Sensitivity
to Weighting Scheme. internal memorandum from P. Hutton to F. Chung, January
24.
Shumway, R.H. Consulting (1993). Statistical Analysis of
Historic Delta Water Quality Data. submitted to DWR Delta Modeling Section,
December 19, Contract No. B59259.
Water Engineering & Modeling (1993). Draft Proposal
for Development of a Transition Matrix Delta Water Quality Model TRANSAL.
submitted to DWR Delta Modeling Section, May 13.
Author: Paul Hutton
Back to Delta Modeling Section 1994 Annual Report Table of Contents
Last revised: 20011115
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