WSPC01844

• File Number: 8283.200
• Description: Colorado River Basin-Colorado River Computer Models-Colorado River Decision Support System-Ray
• State: CO
• Water Division: 5
• Date: 7/13/1994
• Title: Consumptive Use Modeling-Task 1.14b-Consumptive Use Prototype Development-Phase Iia
• Water Supply Pro - Doc Type: Report/Study

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.Task 1.14(b) - Consumptive Use Prototype Development

be constructed, but the user will have the option of changing the baseline scenarios to
construct alternative scenarios.
Once an area and a period of time is selected, the CU model will use a data
management interface (DM]) to retrieve information regarding the area being considered,
for the time frame selected, and the modeling variables needed for the computations. The
D M] will access the various databases and return the data needed for modeling; such as,
crop type, planting dates, livestock amounts and type, municipal areas, population density,
reservoir characteristics, temperature maximum and minimums, etc. These data and
corresponding attributes will be passed back to the CU mode] and an estimated
consumptive use amount will be calculated. ?

2.1.1 Agricultural Consumptive Use .J 'V
Although there are many categories for C?!1S11mp.tiY'~ use, the agricultural category is
probably the most important, this is because 64 to t!91lercent of consumptive use on
upper basin tributaries of the Colorado river is agricultural (according to the U.S.
Bureau of Reclamation Consumptive Uses and Losses Report for 1981-1985).
Agricultural consumptive use is comprised of the irrigated acreage, livestock, and
stock pond categories.

2.1.2 Evapotranspiration Calculation Methods
Agricultural consumptive use is primarily water use by evapotranspiration.
Evapotranspiration is the amount of water used by vegetation growth and evaporation
from adjacent soil or plant foliage. Evapotranspiration is critical to determining the
amount of irrigation water that crops can be expected to consume. j~d <
Evapotranspiration rates are expressed in terms of a length per unit time (LIT){n
metric millimeters are used for length, and in english inches are used for small time
periods and feet for large time periods. To calculate a volume of water used (L31T), the
evapotranspiration rate can be multiplied by an area (L 2l. The consumptive use value
can be expressed daily, monthly or yearly and must reflect the characteristics of the
crop type grown in the area. These characteristics are based on crop curves or crop
coefficients that take into account individual characteristics such as days to maximum
cover, dates of harvest, and water needs. 6t- "':,\( - (i9J~ ~
There will be three methodologies ~al USBR BC, Modified USBR procedIJ~;'
and the Penman Monteith) whici@ be used to calculate the evapotranspirationlThe
methodologies will all be written in FORTRAN and have been obtained from the
following sources:
. The original USBR was obtained from the XCONS2 FOIITRAN program that the
USBR developed. This program has been documented and modified to make it
more structured. This model is being modified to include the CRDSS changes to the
USBR procedures as well as additional routines are being added for calculating
other consumptive uses.
. The reference crop equation (Penman Monteith) is based on s*e routines that
were developed by W.W.Wheeler.
The most important data for estimating evapotranspiration are climate, water supply,
and plant growth characteristics.

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7/13/94 - Draft of Task Memorandum

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IDS Group, CSU