WSP03721

• File Number: 8276.300
• Description: Lower Gunnison Basin Unit - Colorado River Basin Salinity Control Project
• State: CO
• Basin: Colorado Mainstem
• Water Division: 4
• Date: 12/1/1989
• Title: Colorado River Water Quality Improvement Program Lower Gunnison Basin Unit North Fork Area Preliminary Findings Report December 1989
• Water Supply Pro - Doc Type: Report/Study

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CHAPTER II

PIAN FORMULATIOO

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A significant problem identified by SCS in the Tongue Creek drainage is
the inefficient use of a limited water supply. The SCS estimates that 30 to
50 percent of the water diverted to earthen ditches is lost to ditch seepage,
while overall on-farm irrigation efficiencies are presently less than
50 percent. Reclamation studies indicate that a seepage rate of more than
2.0 cubic feet per square foot of wetted perimeter per day (ft/day) would be
necessary to produce these 30- to 50-percent seepage rate values. This is
considered very high.

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The irrigation ditches convey water through permeable soils overlying
Mancos Shale. Seepage water contacting the Mancos Shale dissolves salts and
transports it to the stream system. Surface water diverted for irrigation
has a TOS concentration of less than 200 mg/L.

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Salinity concentrations of Tongue Creek return flows, measured by the
SCS, range from 1,300 to 6,500 mg/L. Salt contribution to the Gunnison River
from the Tongue Creek drainage is estimated by the SCS to be more than
45,000 tons annually.

According to SCS studies, approximately 50 percent of the salt
contribution is caused by excess irrigation water applications and that
irrigation management could reduce the salt contribution by 10,000 tons per
year. This reduction is associated with SCS on-farm management practices only
and does not include canal and lateral lining.

Hydrosalinity

Reclamation's study of the Tongue Creek drainage began with an analysis
of water quality grab samples and daily flow measurements at the Tongue Creek
gauging station located near Cory. The data collected between February 1976
and March 1985 showed an average annual flow volume of 38,940 acre-feet and a
salt load of 44,500 tons. A water quality sU1llllary of Tongue Creek at the Cory
gauge is presented in Table 1.

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Month
January
February
March
April
May
June
July
August
September
October
November
December

Table 1
Average TOS values from Reclamation
grab samples at Tongue Creek near Cory
(February 1976 to March 1985)
Number of
s,les

7
9
8
8
10
9
9
9
10
6
7

Average
TDS
1,236
l,200
1,032
752
l,014
941
1,908
1,970
1,583
1,390
1,166
1,240

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