WSP00401

• File Number: 8443.400
• Description: Narrows Unit - Reports
• State: CO
• Basin: South Platte
• Water Division: 1
• Date: 2/1/1978
• Author: US DoI BoR
• Title: Special Report Investigation of Review Issues Narrows Unit Colorado
• Water Supply Pro - Doc Type: Report/Study

OG'ie

mental water requirements of the major ditch systems within th
area. E~hibit 6 shows the annual farm delivery requirements f
ground-water alternative ,and the quantity of water supplied by
to meet the requirements. With the proposed recharge system,
would occur in 5 of the 28 years studied. The annual farm del
requirement whi,ch was anticipated to be satisfied by recharge \
found to average 42,600 acre-feet and to range from 4,800 acre,
in 1956 to 109,100 acre-feet in 1972.

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The flows estimated to be divertible for recharge were determir
the new conveyance system. Since the average annual river divE
requirements for the combination system are not appreciably dij
than those estimated for the new system, the estimates of the i
water supply capability which were determined assuming an all r
system are considered representative of the potential water su~
capability of the combination system.

Effects of the recharge and pumping operations on the flows of
South Platte River will consist of a combination of stream accr
and depletions. The reason that depletions occur is that pumpa
the average, occurs closer to the river than where the recharge
and there is a time lag for the recharge effects to offset the
effects. The depletions will be minimal, and it is estimated t
about 6 years of operation will be needed for the effects of re
to completely offset the pumping effects on the river, At thi~
appro~imately a total of 5,000 acre-feet of the drain-out water
be available for rediversion in the months of July, August, anc
September. Assuming conveyance losses of 38 percent in the exi
distribution system, 3,100 acre-feet are usable on the farm, 1
results in an average annual supply at the farm headgate of 45,
acre-feet.

Potential Problems

ReCharge Site Selection

Even though the theoretical equations indicate that waterloggin
beneath individual recharge sites may be kept to a minimum, wat
logging due to raising of water tables down-gradient from the r
sites may be a problem. This is particularly true for those ar
that lie relatively close to the river. Exhibit 7 delineates t
areas where the water table generally lies less than 10 feet be
land surface. Any recharge in the proximity of these areas, pa
north of the river from north of Sterling to the end of the stu
has the potential of contributing to already high water tables
gradient from the recharge sites.

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