WSP07957

• File Number: 8276.100
• Description: Grand Valley Unit-Colorado River Basin Salinity Control Project
• State: CO
• Basin: Colorado Mainstem
• Water Division: 5
• Date: 1/21/1983
• Title: Grand Valley Salt Pickup Calculations - Draft Report
• Water Supply Pro - Doc Type: Report/Study

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CHAPTER II

GRAND VALLEY RIVER BUDGET

a base, land usage was updated for each year of the study. Table 2

summarizes the cropping patterns and land utilization for 1969 and 1980.

Based on city water records, the 1969 land utilization was adjusted for

municipal changes for the years prior to 1969.

Table 3 presents the average of the consumptive use values used in the

model. All the values are presented in inches to facilitate their use in the

model, even though it is not normal to present some of the u,ses in this

manner (i.e., industrial). To determine the consumptive use" the values in

Table 3 are multiplied by the acreages from Table 2.

The calculation of consumptive use for the agricultural. lands consists

of using a modified Jensen-Haise method. The modification to the method

consists of using crop curves that are a function of the su" of the Jensen-

Haise potential evapotranspiration (ETP) since the plant date. This method

was developed by the Irrigation Management Service group in the USBR E&R

Center. The Jensen coefficients were developed specifically for the Grand

Valley using neutron probe data, comparing to lysimeter studies, and USBR

weather station data. Crop curves were also modified for the valley.

Consumptive use (ET) calculated by this method compares very well to

lysimeter data and to the Penman Method. The calculations ,:onsist of

generating ETP for the year, then daily ET for each crop, summing to get ET

by crop by month.

Since the data necessary for the Jensen-Haise method was only available

for the period 1972-1980, a different method was used to estimate the

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