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Section 7
<br />Availability of Existing Water Supplies
<br />7.1 Methods and Tools Employed
<br />to Evaluate Surface Water
<br />Supply Availability
<br />The availability of surface water and groundwater
<br />supplies for each basin are summarized in this section.
<br />Physical availability of surface and groundwater
<br />resources must be carefully evaluated against the legal
<br />right to divert, pump, or consume these resources.
<br />Surface water supply availability was estimated at
<br />selected points in each major river basin in Colorado.
<br />Colorado's DSS surface water allocation model,
<br />StateMod, and supporting datasets were the primary
<br />tools used for this analysis when available. StateMod
<br />simulates daily or monthly hydrologic water availability in
<br />a river basin based on a stream's water rights, structures,
<br />and operating rules (http://cdss.state.co.us). For those
<br />basins without StateMod datasets, alternative sources
<br />and studies were used to summarize available water to
<br />the extent possible.
<br />7.1.1 Decision Support Systems
<br />StateMod simulates three types of flow: physically
<br />available, legally available, and naturalized. These terms
<br />are described below. The primary data sources used in
<br />the development of the StateMod input files include
<br />USGS and DWR streamflow measurements, SEO
<br />diversion records, reservoir storage records, basin
<br />studies and reports, and interviews with water
<br />administrators and project owners. Much of the model
<br />input data is stored in HydroBase, the DSS central
<br />database. HydroBase contains historical water rights,
<br />stream gage locations, and real-time and historical
<br />stream flows.
<br />^ Ph~~ic~ll~ Avail~bl~ p~/~ter: The actual or observed
<br />amount of water flowing in the stream. This flow is
<br />measured at a gage or calculated as a function of
<br />historical hydrology less current water uses, and the
<br />effects of storage and conveyance structures. Existing
<br />storage and conveyance capacities are used.
<br />^ L~gally Av~ilabl~ UVat~r: The portion of physically
<br />available flow that is unappropriated, or water that
<br />could be developed without injury to other water rights
<br />or compacts. The water must be first physically
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<br />Statewide Water Supply Initiafive
<br />available, and then the legal restrictions to that water
<br />must be assessed (e.g., downstream calls, compact
<br />requirements, etc.). As with physically available flow,
<br />this calculated flow is a function of historical
<br />hydrology combined with current water use, etc.
<br />Water that is legally available can serve multiple
<br />purposes. For example, water that must be delivered
<br />to a downstream senior right or compact requirement
<br />could provide environmental benefits.
<br />^ Natural9z~d Str~~~fl~v~: The undepleted,
<br />unregulated total water supply that would have been
<br />available absent all human intervention (e.g.,
<br />diversions, storage and releases, return flows, CU).
<br />This calculated flow is the primary input dataset used
<br />for making physically and legally available flow
<br />simulations in StateMod and is often referred to as
<br />"base case." Naturalized flow is also known as
<br />natural, native, or virgin flow.
<br />StateMod runs consist of baseline datasets that were
<br />used to describe water availability in this section.
<br />Irrigation demands that have been included in the DSS
<br />baseline runs described in the individual river basins
<br />reflect 1993 irrigated acreage and crop types for the
<br />Western Slope basins, and 1998 irrigated acreage and
<br />crop types in the Rio Grande Basin. "Current" M&I
<br />demands for all DSS models, except the Rio Grande
<br />Basin, reflect 1996 levels of use, corresponding to the
<br />end-date of the current model study period. In the Rio
<br />Grande Basin, the M&I demand reflects 1998 levels of
<br />use. During the SWSI process, M&I demands for 2000
<br />and 2030 were developed that can be incorporated into
<br />future analyses. While it is important to update M&I
<br />demands for the DSS basins, the incorporation of 2000
<br />water demands will not significantly affect the supply
<br />availability shown in this section. Section 7.4 includes
<br />estimates of 2000 and 2030 depletions and supply that
<br />can be developed under the Colorado River Compact.
<br />Additional information on the DSS models can be found
<br />at: http://cdss.state.co.us/ .
<br />7.1.2 Data Sources
<br />Table 7-1 summarizes the sources of supply data used in
<br />this study to evaluate surface water supply availability.
<br />The Colorado, Gunnison, Yampa, White, Rio Grande,
<br />San Juan, and Dolores Basins have existing DSS
<br />datasets and models. StateMod was therefore used for
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