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Last modified
9/25/2011 10:18:49 AM
Creation date
5/29/2008 12:38:09 PM
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Decision Support Systems
Title
CRDSS Task 1.14-26 - Consumptive Use Model - Irrigation Consumptive Uses and Losses in the San Juan River Basin
Description
This task memorandum formalizes the computation of irrigation consumptive use in the San Juan River basin for water years 1985 to 1990.
Decision Support - Doc Type
Task Memorandum
Date
1/9/1995
DSS Category
Consumptive Use
DSS
Colorado River
Basin
San Juan/Dolores
Contract/PO #
C153658, C153727, C153752
Grant Type
Non-Reimbursable
Bill Number
SB92-87, HB93-1273, SB94-029, HB95-1155, SB96-153, HB97-008
Prepared By
Riverside Technology inc.
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depending on whether the excess rainfall is stored in the soil root zone for later use or lost through <br />deep percolation. <br />A more detailed tabular result is included in Section 4.0. <br />Data Set 2- Alfalfa-Short and Pasture-Short Crops Considered <br />Parts of alfalfa and pasture areas are assigned short. These areas are calculated by using a ratio (area <br />short/total area) that the USBR adopted in the Colorado River System Consumptive Uses and Losses <br />Report, 1981-85 . The ratio is constant for each subarea for each crop (alfalfa, pasture) as shown in <br />Table 3 and is applied to all years. <br />The length of the growing season for alfalfa-short and pasture-short crops is assumed to be equal to <br />the average of the values that are reported in the USBR Colorado River System Consumptive Uses <br />and Losses Report for 1981-85 . Similarly, the specified planting and cutoff dates in the report are <br />averaged in each subarea to obtain equivalent numbers for the 1985-1990 report. Thus, each crop <br />combination is assigned a single planting and cutoff date for all years, though these numbers can be <br />varied in each year. This increases the number of crop-soil combinations to 47. <br />Figure 4 shows the total annual IWR for the whole San Juan River basin computed using the two <br />forms of the SCS Blaney-Criddle evapotranspiration estimation method (SCS Blaney-Criddle with <br />and without enhancements). As expected, the 6-year average annual IWR is lower than the previous <br />data set run, i.e. 170,590 acre-ft (16.0 percent lower) and 211,230 acre-ft (12.8 percent lower) for <br />SCS Blaney-Criddle with and without enhancements, respectively. <br />Figure 5 shows the 6-year average annual consumptive use by subarea. The highest volumetric <br />water use by subarea, by county, and by HU is in Montezuma2 (51,960 and 61,190 acre-ft), La Plata <br />(84,380 and 107,010 acre-ft), and HU14080101 (56,280 and 69,270 acre-ft), respectively. <br />In the USBR Colorado River System Consumptive Uses and Losses Report, 1981-85 , the <br />determination of alfalfa-short and pasture-short areas has become a prerequisite for consumptive use <br />calculation. This is because of the limitation of the XCONS2 program, which does not <br />automatically account for water supply information in the calculation. <br />A more detailed tabular result is included in Section 4.0 <br />3.0 CONCLUSIONS/RECOMMENDATIONS <br />Depending on the level of detail desired, several different data sets can be prepared for estimating <br />IWR in the San Juan River basin. Smaller subareas may be chosen to increase the representativeness <br />of the weather stations. <br />The IWR, as estimated by the SCS Blaney-Criddle method with enhancements, is consistently lower <br />than the estimate of the SCS Blaney-Criddle without enhancements. This is mainly because of the <br />assumption that in the very first year of the estimation, the soil moisture storage is at full capacity. <br />The other factors causing the difference are the winter precipitation contribution to soil moisture <br />storage at the beginning of the growing season, and the difference in the estimate of the effective <br />rainfall. <br />Page 3 <br />A275 03.07.95 1.14-26 Garcia <br />
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