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

Recommendations -Conveyance Efficiencies
As shown in Table 1, conveyance losses for the large ditch systems during the first month
of irrigation range from 30 to 60 percent, with an average near 40 percent. The
conveyance losses later in the irrigation season range from 20 to 35 percent, with an
average near 30 percent. The growing season in the San Luis Valley generally extends
for about five months, from mid April through mid September. Therefore, the first
month of irrigation is approximately 20 percent of the entire irrigation season.
StateCU currently uses one annual conveyance efficiency estimate for each ditch system.
For the six ditch systems shown in Table 1 with estimated losses for both the first month
of irrigation and subsequent months, the annual conveyance loss was estimated by the
following equation:
Annual Loss (%) _ (0.20 * % First Month Loss) + (0.80 * % After First Month Loss)
Conveyance Efficiency (%) = 100 -Annual Loss (%)
Estimated first month losses for the Empire Canal were not available. The Empire Canal
second month losses were similar to the Prairie and Excelsior ditches, therefore, a
conveyance efficiency of 75 percent is recommended. Table 2 shows the recommended
conveyance efficiencies for the large Water District 20 ditch systems.
Table 2
Recommended Conve ance Efficiencies for Lar a Water District 20 Ditches
Ditch S stem Conve ance Efficiencies
Rio Grande 65
Farmers Union 62
San Luis Valle 63
Prairie 78
Excelsior 78
Em ire 75
Monte Vista 68
As noted above, methodologies that require detailed information regarding wetted
perimeter and flow velocities are not appropriate for use in the RGDSS basin-wide
analysis because this information is generally not known. The data-centered approach
used for the historic crop consumptive use analysis requires information to be developed
or estimated basin-wide using available data from GIS coverages or Hydrobase.
Information regarding conveyance efficiency is only available for the larger ditches in the
basin, therefore, a method is required to estimate conveyance efficiency for shorter,
smaller capacity ditches. The MRCS has developed conveyance efficiency curves that
can be used to estimate ditch efficiency based on soil type and canal loss -information
that is available or can be developed from GIS coverages for the Rio Grande basin for
ditches less than one mile in length. These curves are appropriate for use when more
detailed information on wetted perimeter and flow rate is not available. Figure 9 shows
appendB_cropcu_6-2004.doc B-11 of B-19 12/13/00