WSP01329

• File Number: 8276.400
• Description: McElmo Creek Unit - Colorado River Salinity Control Program
• State: CO
• Basin: Colorado Mainstem
• Water Division: 7
• Date: 1/1/1981
• Title: McElmo Creek Salinity Control Unit
• Water Supply Pro - Doc Type: Project Overview

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McElmo Creek Salinity Control Unit

McElmo Creek is located in southwestern Colorado and drains approxi-

mately 720 square miles. About 150 square miles is agricultural land

located in the eastern portion of the drainage, around Cortez (see figure

1), The agricultural land contains 28,000 irrigated acres in the

Montezuma Valley Irrigation District, and 3,000 irrigated acres in the

Summit Irrigation District.

McElmo Creek flows through the southern half of the drainage basin

at an average of 32,400 acre-feet annually, McElmo Creek carries about

115,000 tons of salt annually past the Colorado-Utah State line to the

San Juan River, The San Juan River is a tributary to the Colorado River,

McElmo Creek has acquired 85 percent of its salt load by the time it

is past the Mud Creek confluence (see figure 1). Except for spring runoff,

the majority of this water is irrigation return flow, The majority of

water below this point is natural runoff, Some water is diverted below

Mud Creek for irrigation and its return flow re-enters McElmo Creek before

it passes the State line.

Soils in the basin can be divided into three types, The Billings

(gray) soil series, which is alluvial in origin, covers most of the far

eastern and southeastern portion of the drainage basin. The Monticello

(red) so:l series, derived from Dakota Sandstone and aeolian in nature,

covers the north and western portion of the drainage. Between these two

soils is an area of exposed monocline dakota formation which can vary from

sand to adobe clay. Soil tests indicate the irrigated gray soils have the

potential of producing eight times as much salt as the irrigated red soils.

Gray soils can annually produce 9.6 tons of salt per acre-foot of deep-

percolated water (TAF) , whereas red soil only produces 1,2 TAF.

The Montezuma Valley Irrigation (MVI) Company is responsible for

delivering the irrigation water, which is diverted from the Dolores River.

This water contains around 175 milligrams of salt per liter of water (mg/L).

McElmo Creek water leaving the basin contains about 2,600 mg/L. This salt

loading accounts for 12 mg/L of salinity at Imperial Dam, or about 1.5

percent of the total salt in the Colorado River,

There is presently a ground water research program consisting of

125 wells within the basin which are monitored for water table elevation,

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