WSP11780

• File Number: 8443.400
• Description: Narrows Unit - Reports
• State: CO
• Basin: South Platte
• Water Division: 1
• Date: 5/1/1973
• Author: US DoI BoR
• Title: Narrows Unit Definite Plan Report
• Water Supply Pro - Doc Type: Definite Plan Report

#l r.. ,.. l)
1 L,' JG

Reimbursability of Costs

Reimbursable and nonreimbursable allocations have been redetermined
and the comparison with the 1969 Reevaluation Statement is shown in
Table 6.

Repayment

Irrigation

The previous analyses of the irrigation water supply for the
Narrows Unit indicated that there would be an average annual transporta-
tion loss of 38 percent between Narrows Darn and the farm headgate.
The "Point Flow" hydrology study showed the South Platte River between
Narrows Dam and the Colorado State line to be a gaining stream on an
average monthly basis. These results were supported by a study of
the gains and losses in the South Platte River made by the U. S.
Geological Survey. Therefore it was assumed that there would be no
river losses and the 38 percent losses would occur in the irrigation
distribution system.

As a part of their contract negotiations with the water users,
the Lower South Platte Water Conservancy District (LSPWCD) employed
a consultant to determine if losses would occur between Narrows Dam
and the downstream delivery points. The consultant concluded that
average annual river losses of between 10 and 12 percent would occur.

Subsequently, discussions were held with members of the Colorado
State Engineers Office and the LSPWCD. The State Engineer is responsible
for the administration of water rights and the delivery of water and
therefore has had many years of experience in the operation of the
involved stretches of the South Platte River. Based on that experience,
it was suggested that for planning purposes, average annual river losses
of one-half percent per mile be assigned from Narrows Dam to Balzac
and 1 percent per mile to delivery points below Balzac. The application
of these loss figures would result in average annual river losses of
about 20 percent.

In consideration of the discussions with members of the State
Engineer's Office and of the finding of the LSPWCD consultant's report,
it has been concluded that river losses will be assessed to storage
water released from Narrows Dam. However, it has been assumed that the
regime of the South Platte River with the Narrows Unit in operation
would be different than it has been historically. There will be sub-
stantially greater volumes of water in the river, particularly during
the irrigation season, than has occurred during the past. In addition,
future management practices should be adopted that will reduce losses.
Therefore, it has been agreed that the assignment of average annual river
losses of 15 percent would be appropriate for determining the payment

19