FLOOD02454

• County: Gunnison
• Community: Uncompahgre Valley
• Basin: Gunnison
• Title: Uncompahgre Valley Reclamation Project - Hydropower - Part 2 - AB Lateral Unit Water Supply Study
• Date: 12/1/1988
• Prepared For: Montrose Partners and Ucompahgre Valley Water Users Association
• Floodplain - Doc Type: Project

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2.2.3 Return flows

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The third major contributor to irrigation supplies is the irrigation
return flow which enters the river from small streams and ditches at
numerous locations along the Uncompahgre River. Return flows are not
monitored by the UVWUA; hence it is difficult to estimate the quantity with
any accuracy. For purposes of this report, the return flow contribution has
been estimated to be a total 20 cfs and is assumed to enter the river at
three locations downstream of the South Canal outfall. This estimate is
based upon discussions with current and past UVWUA General Managers.

Principal tributaries to the river within the study area include
Horsefly Creek from the west, and Dry Cedar and Cedar Creeks from the east.
As with return flows, flows from these streams have not been gauged or
monitored. Flows in these streams are dependent upon snowmelt and storm
runoff during the early spring, and carry irrigation return flows during the
late summer and early fall. Simulated flows for Horsefly Creek (see
Appendix A) were obtained for this study from the Colorado Water Resources
and Power Development Authority (Authority). The Authority is presently
conducting a study of the Upper Gunnison and Uncompahgre Basins which
includes the development of a water budget model of the two basins. The
model was developed by WBLA, Inc. For this report, it has been assumed that
flows from Horsefly would be available to meet irrigation needs in the
Loutzenhizer Canal.

For Dry Cedar Creek, an assumed inflow pattern was adopted. This
pattern was based upon observations by the UVWUA. Because Cedar Creek
discharges into the Uncompahgre River downstream of the Selig Canal, no
inflows were assumed for the existing conditions model.

Table 2.4 summarizes the assumed monthly patterns of return flows and
losses for existing conditions.

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Table 2.4
Assumed return flows (UG1, UG2, UG3 and Dry Cedar)
and demands (SCL, UP1, UP2), in cfs.
Dry
Month UG1 UG2 UG3 Cedar SCL UP1 UP2
Jan 0 0 0 0 8 10 0
Feb 0 0 0 0 8 10 0
Mar 0 0 0 0 8 10 0
Apr 5 5 10 4 38 5 8
May 5 5 10 5 68 23 33
Jun 5 5 10 10 88 28 41
Jul 5 5 10 15 88 30 43
Aug 5 5 10 15 88 30 43
Sep 5 5 10 5 48 15 21
Oct 4 4 8 4 8 0 0
Nov 2 2 4 0 8 10 0 .
Dec 0 0 0 0 8 10 0
Volume 2,180 2,180 4,360 3,529 28,210 10,955 11 , 482
-2.12 -