BOARD01897

• Board Meeting Date: 3/10/1998
• Description: CF Section - Groundwater Appropriators of the South Platte - Approval of a Construction Fund Authorization in Amount of $1.7 M for Construction of the Sedgwick Augmentation Reservoir
• Board Meetings - Doc Type: Memo

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· The pumping water level in the wells does not drop below 30' from the surface elevation
of the wells. Based on field pump testS from Canfield Drilling,
· A 24" High Density Polyethylene (HOPE) or equivalent (c= 140) pipeline delivers the
water to the reservoir site, The sizing needs to be large enough to keep the overall total
dynamic head below 85 feet.
. The reservoir normal high water surfaCe elevation is below 3,570' msl.

The wells will require the construction of a manifold and pipeline delivery system to be used for this
project, Additional studies at the preliminary level should be done to determine if phasing the project
with later construction of this connection would work technically as well as economically, This well
system does offer one alternate to fill the fmal 500 acre-feet of storage in the reservoir once gravity
diversions from the Peterson Ditch are no longer feasible,

A second alternate for topping off the reservoir would be to install a new pumping station at the
proposed Peterson release structure. These pumps would be low head and have a shorter pumping
distance to the reservoir. This alternate should be explored further at the preliminary design stage to
determine the flexibility that a forebay/pumping plant would bring at this location, Figure 2
illustrates the locations of the possible water supply sources in regards to the proposed reservoir site.

The delivery of water to the proposed reservoir can be accomplished through the combined use of the
Peterson Ditch and the either the "Ovid Wells" or a pumping plant on the Peterson Ditch. Gravity
diversions from the Peterson Ditch will be capable of filling approximately 1,700 acre-feet of the
2,230 acre-feet of total capacity, or roughly 75%.

The "Ovid Wells" are capable of supplying water to the reservoir for topping it off, but the operation
of the wells will be more costly than the diversions from the Peterson Ditch. A preliminary cost
estimate, based on current power costs, indicate the pumping costs associated with using the "Ovid
Wells" to fill the reservoir would cost approximately $7.50/acre-ft.

C Water Deliveries to the South Platte River
The reservoir would release water to the South Platte River through two methods, The first option
would be an existing open channel running from the Southeast comer of the reservoir, following the
existing drainage slough back to the river, The second option would be accomplished by reversing
the flow in the pumping pipeline from the GASP Ovid wells and allowing water to flow by gravity
back to the river.

The present capacity of the open channel and slousJI back to the river may not allow for all releases
to go back to the river. There is a culvert through the railroad that is probably under capacity. There
would also be some channel grading improvements that would be required if the Ovid Well pipeline
manifold was not constructed, There is adequate property to construct these improvements and it is
technically feasible, The sizing will depend on final operational decisions made at the preliminary
design phase.

The release structure for the reservoir will be sized between a 50 to 60 cfs maximum capacity. This
capacity was modeled with daily gage flow records at Julesberg. Some simplistic assumptions were
made in the modeling with regard to flows available for diversion, It allowed the 2,000 acre-foot
reservoir to actually regulate an average annual diversion ranging between 1,800 to 2,400 acre-feet
depending on assumed operating conditions, This was based on an all or nothing approach to
releases. If the release capacity from the reservoir was not adequate to bring flows up to 120 cfs,
then the reservoir was not operated. This approach could supplement flows at the State line on up to

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