BOARD00123

• Board Meeting Date: 1/27/2004
• Description: WSP Section - Statewide Water Supply Initiative ‎(SWSI)‎ Status Update
• Board Meetings - Doc Type: Memo

COM

DRAFT SWSt Methodology for Estimating .,
Available Water Supply

, .,

The Colorado, GWU1ison, Yampa, White, and San Juan/Dolores Basins have existing
CDSS datasets and models. For these basins, the StateMod water resources planning
model and supporting datasets will be used to estimate physically and legally
available water. The datasets for the Rio Grande are still being revised, but it is
expected that they will be available to use as part of this task.

.

For those basins without developed CDSS datasets-Arkansas, South Platte, and
North Platte-information for physically and legally available flows will be gathered
from existing sources and studies.

While the physical availability of water can be evaluated using historic observations,
the legal availability of water is only a portion of the observed flows and will in
general be determined by using some type of model or analysis tool that accounts for
the Prior Appropriation Doctrine and operational policies in effect in the basin. In
those basins with CDSS datasets, the StateMod data will be used to estimate available
flows. In addition, the CDSS datasets contain naturalized flows, or baseflows, for the
basin.

River flows could be evaluated at selected locations with the appropriate water
supply summary. These locations will be established as the project evolves. It is
anticipated that up to five key locations will be identified within each basin, based
upon such factors as hydrologic delineations, basin administration practices, location
of future water demands, and superior conditional decrees.

.

Methodology for Basins with Existing CDSS Datasets

CDSS datasets and StateMod models have been developed for the Colorado,
Gunnison, Yampa, White, San Juan/Dolores, and Rio Grande River Basins. The
StateMod model represents the hydrological, structural, and administrative feature of
the river basin. Model datasets contain all necessary time-series data and information
to simulate the allocation and distribution of water according to the Prior
Appropriation Doctrine. Direct flow, instream flow, storage and operational rights,
and permitted well rights are simulated as a function of water availability, priority,
decreed amount, demand, structure capacity, and location.

The current CDSS modeling system focuses on datasets in the following
configurations:

1. Historical Dataset ("H"). Simulate historical events. This case is used to estimate
naturalized flows and to calibrate physical parameters of the models (e.g., by
adjusting delay tables for diversion return flows and verifying the estimated
streamflow time series). The historical diversions are used as demands. For
reservoirs in the historical dataset, the end of month content is set to zero for the
time before the reservoir existed, effectively eliminating the reservoir from the
model during that period. Water rights can also be turned on and off during the
modeling period. The results from this dataset are mainly used to validate and

.

2

S:\TASK 8 & 9 SUPPLY AND DEMANDlSWSIWATERSUPPL YMETHODOLOGY_l-tj.Q4,DOC