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

1"'1
~
t\

"., ""I
-,
,
~

'~
~~
t,

'1
"'
';.,..-',
,'.-
L

r~

-:.\.

~~:~
"'1
,
,....-

f}!
':."
~4

~]
X>JJ

.(..;')

S('~"

~~~
~ .~
""",.,
...:</1

~~>~
;:: :~
Li

r:~l~
-~
"

r1
ti',
&A

t;)
t;..i
i.,;,
~;:

~:~
~--

CHAPTER II

PIAN FORMULATIOO

Homestretch, Hotchkiss, McDonald, Old Agency, OUray, pinion, Reservation,
Stark-Volkman, and Upper Uncompahgre. The ditches divert water directly from
the Uncompahgre River and, except for the Stark-Volkman Ditch, are above the
uncompahgre Project service area.

winter diversion r}ghts are held by only thfee ditch systems,
MCDonal~ Ditch (lO. 0 ft Is), OUray Ditch (4.0 ft Is), and pinion Ditch
(7.5 ft Is). The Colorado Division of Water Resources indicates that eight
di tches are known to divert winter water, the two not diverting are the
Homestretch and Reservation. winter diversions do not injure senior water
rights and the Division of Water Resources does not administer winter
diversions as is evident by the lack of winter diversion records. Since the
Tri-County Water Conservancy District rural domestic water distribution system
has a major trunkline in this area with excess capacity, the Colona area was
analyzed to determine its potential for cost effective salinity control by
implementing a winter water replacement program.

Hydrosalinity

Reported estimates of the ditch headgate capacities were greater than the
irrigation water right for five ditch systems, less than the irrigation water
right for three ditches, and equal to the irrigation water right for one
ditch. A capacity estimate was not available for the Reservation Ditch.
Because of these discrepancies it was assumed that ditch headgate capacity was
equal to the irrigation water right and a monthly diversion hydrograph was
estimated for each system.

In this analysis, base flow concentration is defined as the TDS
concentration that ground water reaches after all possible chemical reactions
have taken place, or point of equilibrium where forward and reverse reaction
rates are equal. The base flow concentration of 842 mg/L is the average TOS
concentration of 21 privately owned wells sampled once during June 1977 and
five privately owned wells sampled once during August 1971. Reclamation
installed two observation wells within the area which were sampled
periodically over a 3 year period. A plot of the wells' water table elevation
and TOS concentration over the observation period indicated that the TOS
concentration does not vary appreciably over time. This plot indicates that
TOS concentration data from wells sampled once, could be used to characterize
the areawide long-term base flow concentration.

Nine of the ten ditch systems in the Colona area divert water from the
Uncompahgre River above the Uncompahgre Project. Therefore the inflow TDS can
best be defined by the TOS concentration of the Uncompahgre River at the
Colona gauge. Monthly average TOS concentrations for the Uncompahgre River at
Colona are presented in Table 5.

Seepage rates were determined from laboratory permeability tests on l71
samples from 95 auger holes in the Colona area. These tests were conducted
for land classification studies for the Dallas Creek Project. The analysis of
this data indicates a possible range of seepage rates from 0.l7 to 0.32 feet
per day. Monthly wetted areas for each system were determined from a wetted

16

000942