PROJ02106

• Contract/PO #: FS0063FX
• Contractor Name: Groundwater Appropriators of the South Platte
• Contract Type: Miscellaneous
• Water District: 0
• Loan Projects - Doc Type: Feasibility Study

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GASP Ovid Reservoir Feasibility Study

I. Introduction

The Groundwater Appropriators ofthe South Platte River Basin (GASP) have sponsored this
study to address the feasibility of constructing an off stream augmentation reservoir near the
Colorado-Nebraska border. The objective ofthe study was to identify constraints associated
with construction of the reservoir and to analyze the effectiveness ofthe reservoir in achieving
the primary function ofre-regulating the flows in the South Platte River at the Nebraska State
line. Re-regulation of flows in the South Platte River will benefit GASP members by increasing
flows at the State line during the irrigation season and thus augmenting well depletions.

The lower section ofthe South Platte River is defined as the reach of the river from the west
boundary of Washington County to the Colorado-Nebraska State line. This reach of the river is
commonly known as Water District 64. The South Platte River Compact requires the State of
Colorado to administer water rights with adjudicated priority dates junior to June 14, 1897 in
such a way that diversions in Water District 64 do not diminish the flow below 120 cubic feet per
second (cfs) at the State line during the period from April I-October 15.

Although the South Platte River has seen an overall increase in flows due to urbanization,
agricultural practices, transmountain diversions, and groundwater development, the flow at the
State line still drops below the 120 cfs compact threshold. Many times the natural flow in the
river will not meet compact entitlements even with a curtailment of diversions in District 64.
But the possibility for Colorado surface water users in Water District 64 that are junior to June
14, 1897 to have to cease diversions is still a concern of water users.

The South Platte River in Water District 64 is a gaining reach of river. This means that return
flows to the river tend to increase progressively as it moves towards Nebraska. Approximately
300,000 acre-feet per year in excess ofthe compact entitlement flow into Nebraska every year.
However, the majority of these excess flows occur in the winter months due to the lag time for
return flows from irrigated agriculture to enter the river. The proposed reservoir's primary
function will be to provide replacement water for augmentation of its member wells and in doing
so will often times meet Nebraska's compact entitlement. By meeting the flow threshold of the
compact, the potential of GASP members being forced to cease diversions during critical periods
would be reduced.

GASP has previously commissioned a feasibility study for a reservoir site on the north side of
the river approximately 3 miles upstream ofthe Ovid reservoir site and for reservoir sites on the
south side of the river in the same approximate geographic area. Tuttle Applegate, Inc.
completed the study for the north side reservoir in February 1998 and the south side reservoirs'
study was completed in March 1997 by The Sear-Brown Group. Due to environmental issues,
the site on the north side ofthe river near the Town of Sedgwick, had enough unknown factors
with regard to permitting and mitigation that other sites were determined to be better candidates.
The results ofthe south side reservoirs' study indicated that construction of an off-channel
reservoir in the uplands sites chosen for study were not conclusively a good choice for a re-
regulation project. This work is an extension of evaluating reservoir sites on the north side of the
river to determine ifthere are better alternates.

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