RGDSS_Historic_CUreport_20040601

• Title: RGDSS - Rio Grande Historic Crop Consumptive Use Analysis
• Description: The documentation is for the Rio Grande Basin Historic Crop Consumptive Use Analysis, developed during the RGDSS implementation for the period 1950 through 2002. It includes 100 percent of the crop consumptive use in the basin for the period. Documentation consists of the final Historic Crop Consumptive Use Analysis Report and supporting appendices.
• Decision Support - Doc Type: Modeling Dataset Documentation
• Date: 6/1/2004
• DSS Category: Consumptive Use
• DSS: Rio Grande
• Basin: Rio Grande
• Contract/PO #: C153863
• Grant Type: Non-Reimbursable
• Bill Number: HB98-1189, SB99-173
• Prepared By: Leonard Rice Engineering

- Prairie Ditch 65%
- Rio Grande Canal 56%
- San Luis Valley Canal 75%
Although these efficiencies do not necessarily match the efficiencies indicated by the
ditch companies during the user interview process; they fall well within the range of
recommended conveyance efficiencies for the large ditches.
Application efficiencies used by the consultant in their analysis were as follows:
- Farmers Union Canal 50%
- Prairie Ditch 52%
- Rio Grande Canal 61%
- San Luis Valley Canal 63%
Note that these are actual application efficiencies, not maximum efficiencies required
for the consumptive use analysis. However, these application efficiency estimates are
within the range for 1977 when flood irrigation was being replaced with sprinklers.
The 1978 report Water and Related Land Resources -Rio Grande Basin Colorado,
published by the USDA and the CWCB, indicated that "All consumptive use and
irrigation requirement calculations are based on 29 percent efficiency (including
conveyance and farm losses)". This estimate is within the suggested range of system
efficiencies. It is closer to the minimum efficiencies, which is expected because the
extensive changeover to sprinkler systems was still on going through the 1970s.
• The 1987 report "San Luis Valley Confined Aquifer Study", by HRS, indicated a 50
percent efficiency for the Rio Grande Canal. This figure includes conveyance and
application losses. This is close to the recommended maximum overall efficiency for
the Rio Grande Canal, as the majority of the canal is sprinkler irrigated.
Comments and Concerns
Historic water supply-limited consumptive use estimates are relatively sensitive to both
conveyance efficiency and maximum application efficiency. Analyses were simulated to
determine the level of sensitivity for the recent period from 1990 through 1997. When the
input files for the RGDSS historic consumptive use simulation were revised to reflect
conveyance efficiencies 5 percent higher than the efficiencies recommended in this
memorandum (for instance from 80 percent to 85 percent), the resultant water supply-
limited consumptive use from surface water basin-wide increased by 5 percent. When the
conveyance efficiencies were decreased by 5 percent, the consumptive use from surface
water decreased by 6 percent.
Similarly, when the recommended maximum application efficiencies for flood and
sprinkler use were increased to 65 percent and 85 percent respectively, the water supply-
limited consumptive use from surface water increased 6 percent. When the flood and
appendB_cropcu_6-2004.doc B-18 of B-19 12/13/00