WSP01644

• File Number: 8170
• Description: Arkansas Basin Water Quality Issues
• State: CO
• Basin: Arkansas
• Date: 3/14/1997
• Author: Bradford Austin
• Title: Report to the Commissioner of Agriculture - Ground Water Monitoring Activities - Arkansas River Valley Alluvial Aquifer 1994-1995
• Water Supply Pro - Doc Type: Report/Study

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of the river are the direct result of recharge from applied irrigation water and precipitation, Prior
to the practice of diverting surface water for irrigation, ground water levels were not high enough
to maintain river flow throughout the year for the length of the river. In some areas the sand and
gravel did not contain any water at all. With the application of surface water for irrigation, water
began percolating into the alluvium beneath the fields and the water table rose, As a result of
consumptive losses, due to evaporation and evapotranspiration, recharged ground water is higher
in dissolved solids than the applied irrigation water, This creates a general increase in dissolved
solids concentration in a down-gradient and down-valley direction within the alluvial aquifer.

A long term water budget of streamflow shows the Arkansas River to be a gaining stream
as a large part of the ground water recharge ultimately seeps into the river, Therefore the trend in
surface water quality is an increase in dissolved solids concentrations in the river in a down-valley
direction,

IRRIGATION PRACTICES

With the exception of dry land wheat and pasture, most crops in the area are irrigated, The
main crops grown in the study area and their irrigated acreage is:

1. Hay
2, Com
3, Sorghum Grain
4, Winter Wheat
5, Vegetables
6, Dry Beans
7, Barley
8, Oats

122,400
54,600
20,300
19,700
8,600
4,200
1,200
1,000

The data for irrigated acreage in the study area by crop were based on 1992 agricultural
statistics data from the Colorado Department of Agriculture.

METEOROLOGY

Based on U.S, Weather Bureau data, the climatic regime of the surrounding area would be
classified as semi-arid, Mean annual precipitation in the area ranges from approximately 11 inches
to 14 inches per year, Over 75 percent of the precipitation occurs during the period of April
through September, Based on published information from the Colorado State Engineer's Office,
the 100 year 24 hour precipitation event is approximately 4,5 inches and the 10 year 24 hour
precipitation event is 3 inches, Normal annual Class A pan evaporation for this area is
approximately 65 inches to 70 inches per year with the majority occurring during the May through
October period, The general prevailing wind direction pattern is from the north and northeast,