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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The location of the Peterson Ditch, and the fact that the ditch would be able to provide a gravity
supply, make it ideal for a water supply source for the proposed reservoir. Although the Peterson
Ditch is an efficient and cost effective source for filling the reservoir, certain limitations are
associated with using the Peterson Ditch to deliver water to the reservoir. The diversions
through the Peterson Ditch will primarily occur during the winter months when sub-freezing
temperatures are highly possible. Freezing temperatures could prevent diversions due to icing
and the possibility of ice jams. The timing of diversions may help eliminate this problem. There
is a fairly lengthy time period during the winter months when the flows in the river are high
enough to support this re-regulation project. It appears there is sufficient time in moderate
temperatures to divert a full supply to the reservoir. These are operational issues that would have
to be considered as the project moves forward.

c. Water Deliveries to the South Platte River

The reservoir would release water to the South Platte River through an existing flood control
drainage channel for the town of Ovid. The release structure for the reservoir will be sized with
a maximum capacity between 50 - 60 cfs. In preliminary modeling, an outlet capacity of 50 - 60
was capable of meeting the augmentation needs of GASP in this reach of the river. The flood
control drainageway will need to be evaluated as to the rehabilitation and improvements ofthe
structure required in order for the drainageway to efficiently convey the releases from the
reservoir to the South Platte River. The flood control channel being considered for inclusion in
the project was a part ofthe SCS Sedgwick Sand Draw reservoir project that was constructed to
provide flood protection to the area. This channel has not had any regularly scheduled
maintenance over the years. The proposed reservoir project includes rehabilitation work on the
existing channel as well as future continuing maintenance of the channel. This feature will
provide an added benefit to the local community.

D. Water Supply

The water supply for an off channel reservoir would be dependent on either a junior water right
for diverting water or the transfer of a senior right. Flows in the South Platte River significantly
increase during the winter months due to return flows entering the river. There is generally no
call on the river during the winter months, which would allow a junior diversion to the reservoir
to operate. This would provide the prime opportunity for diverting water to the reservoir.

The historic gage flows in the river at Julesberg have exceeded the 120 cfs threshold during the
April 1 st to October 15th compact time period. This would indicate that a reservoir could divert
some water during this time period as well and store it for reregulation when the flow in the river
drops below 120 cfs at the state line. This would allow the reservoir the ability to fill and refill
in one season when conditions were right.

The results of this study conclusively shows that the winter flows in this reach of the river are
adequate to fill a reservoir of this size the majority ofthe time. Flow records for the South Platte
River were analyzed for a 30-year historic study period (1966-1996). One can assume from
historic records that any other diversions that occurred during the winter months would be
reflected in the gage and that the recorded flows would be in priority for a junior diversion on the
lower reach of the river. The information available indicated that in all but two of the years
(1977 & 1978), there would be adequate flows in the river to allow for the diversions needed to

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