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<br />ALTERNATIVE 11
<br />COMBINED MAINSTEM STORAGE
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<br />This alternative includes both pro-
<br />posed upstream and downstream
<br />mains tern storage projects (Alterna-
<br />tives 2 and 8), Upper mainstem stor,
<br />age would allow for deliveries of an
<br />estimated 30,800 acre-feet for munici-
<br />pal use. Downstream mainstem stor-
<br />age would result in deliveries of 93 ,000
<br />acre-feet per year. The combination of
<br />both of these proposed reservoirs
<br />would result in deliveries totaling
<br />123,800 acre-feet.
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<br />Evaluation
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<br />The market-valued outputs of this
<br />alternative would be irrigation water,
<br />municipal and industrial water. hydro-
<br />electric power and flood protection,
<br />Net annual economic benefits are esti-
<br />mated to be $33.2 million, This
<br />amounts to a5.2 percent rate of return
<br />on the estimated required investment
<br />of $636 million,
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<br />Development of these storage pro-
<br />jects could result in the expansion of
<br />the employment sector and the subse-
<br />quent expansion of government and
<br />services, Flood control benefits would
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<br />ALTERNATIVE 12
<br />CONJUNCTIVE SURFACE
<br />WATER/GROUND WATER USE
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<br />Two plans for the conjunctive use of
<br />surface and ground water were consi-
<br />dered: the lower South Platte River
<br />system and the Beaver-Badger sys-
<br />tem, The two systems have been
<br />assumed to deliver a total of 129,000
<br />acre, feet annually,
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<br />Many senior water right users in the
<br />South Platte River basin presently
<br />suffer injury due to the pumping of
<br />alluvial ground water by wells with jun-
<br />ior rights that were constructed prior
<br />to Colorado's water rights administra-
<br />tion system in 1969, These senior
<br />water users have developed a water
<br />management plan in order to supple-
<br />ment surface water use with potential
<br />high capacity wells, Their plan would
<br />be facilitated by a downstream main-
<br />stem reservoir approximately one-half
<br />the size of the proposed downstream
<br />mains tern reservoir (Alternative 8),
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<br />The Beaver.Badger Water Conser-
<br />vancy District also has formulated a
<br />conjunctive use plan for surface water
<br />and ground water. The plan would
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<br />consist of both surface and subsurface
<br />storage, change of a water right to an
<br />alternate point of diversion and
<br />change of storage rights to an alter,
<br />nate point of diversion.
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<br />Evaluation
<br />
<br />The market-valued outputs of this
<br />alternative would be irrigation water.
<br />Net annual benefits are estimated to
<br />be $2,5 million, This amounts to a 3,2
<br />percent rate of return on the esti-
<br />mated required investment of $76
<br />million,
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<br />be achieved with the combined main-
<br />stem reservoirs. This alternative could
<br />affect fish and wildlife species in the
<br />basin, including impacts on migration,
<br />patterns and habitat of waterfowl and
<br />shore birds,
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<br />Assuming that a downstream main-
<br />stem reservoir was constructed as
<br />part of the lower South Platte conjunc,
<br />tive use plan, some regulation of flood
<br />flows might be achieved,
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<br />With the increased diversion and sub,
<br />sequent increase in irrigation. concen-
<br />trations of dissolved solids and
<br />selected nutrients in the irrigation
<br />return flows would tend to change
<br />downstream water quality, Impacts
<br />would be similar to those of Alterna-
<br />tive 8 if a lower mainstem reservoir
<br />was constructed.
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