S5_11-15-04

• Basin: Statewide
• Title: SWSI Phase 1 Report - Section 5 Projected Water Use
• Date: 11/15/2004
• Author: CWCB
• SWSI - Doc Type: Final Report

Section 5
Projected Water Use
The StateCU model also calculates water supply limited A more detailed description of the StateCU calculation
(WSL) crop CU values associated with each diversion method can be found at http://cdss.state.co.us/.
structure in the basin. These values represent the net CU
of the crops as limited by available water supply and 5.1.2.2 Existing Demands Method:
current irrigation practices, and are calculated as Basins without DSS Models
functions of historical diversions and soil moisture For those basins without developed DSS data sets, the
carryover. Arkansas, South Platte, and North Platte, quantification
and characterization of agricultural uses focused on
It follows that the IWR values can be viewed as a historic diversions, irrigated acreage, and crop type
demand associated with the crop requirements, while the distributions gathered from existing sources and studies.
WSL values represent the actual flow reaching and being
used by the crops (supply). In this way, existing For the Arkansas Basin, agricultural demands were
shortages in agricultural supply can be estimated as: estimated using IWR values acre-feet per acre per year
(AF/Ac/Yr) developed from the State of Colorado's HI
Shortage = IWR- WSL (5.1) Model and irrigated acreages estimated from information
provided by CWCB, DWR, and the USDA Census of
For this project, annual average IWR and WSL values Agriculture.
were aggregated by water district. Existing agricultural
water shortages were then calculated for each water For the South Platte and North Platte Basins, agricultural
district in each basin using Equation 5.1. These results demands were estimated using preliminary estimates of
are presented and discussed in Section 5.3. IWR values and irrigated acres developed during
Table 5-4 summarizes the sources of agricultural preliminary work on the South Platte DSS.
demand information for each basin. For the DSS basins, Summaries of the agricultural demand sources for these
only calendar years 1975 through 2002 were used for the basins are included in Table 5-4.
analysis of agricultural use, even though longer periods
of record are available. Data associated with years prior 5.1.2.3 Future Demands Method
to 1975, because of changes in irrigated acreage and Future (2030) agricultural water requirements were
historical diversions, are not considered to be well-
estimated by basin using annual average requirements
representative of current conditions. on a per acre basis, and projected future irrigated
Table 5-4 Agricultural Demand Information Sources acreage. The current requirements (AFY) are normalized
" • ' ' " ' ` ° to the current irrigated acreages (AF/Ac/Yr) and
~ ~ _ ~ ~ ~_ ~ ~ _ ~ ~ ~ _ ~ ~„~ ~ ~ multiplied by the projected 2030 acreages to arrive at a
~, . future total agricultural requirement (AFY). In other
Arkansas HI Model, 1997-2000 HI Model 1950 - 2000 words,
DWR, USDA
Census of 2030 Ag Irrigation Water Requirement (AFY) _
Agriculture Current Average IWR Requirement (AFIAc1Yr) x
Colorado DSS 2000 DSS 1975 -1990
Dolores/ San DSS 2000 DSS 1975 -1990
Projected Irrigated Lands (Ac) (5.2)
Juan/ San
Miguel
where
Gunnison DSS 2000 DSS 1975 - 2000
North Platte CWCB 2001 Preliminary 1993 - 2002 Current Average Requirement (AFIAc1Yr) _
work on Dss IWRICurrent Irrigated Lands (5.3)
Rio Grande DSS 1998 DSS 1975 -1997
South Platte CWCB 2001 Preliminary 1993 - 2002 2030 WSL CU; incidental losses, livestock watering, and
work on DSS
Yampa/ DSS 2000 DSS 1975 -1990
stock pond evaporation; and gross diversions were
White/ Green estimated using the same approach (Equations 5.2 and
5.3). Projected WSL values represent anticipated crop
CU, assuming the ratio of available supply to irrigated
~
$~ole'ri~ice Wo~e' $upplY Initia~ive
~~
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