PUB00108

• Year: 1986
• Title: St. Vrain Basin Reconnaissance Study
• CWCB Section: Administration
• Author: Colorado Water Resources and Power Development Authority
• Description: Extensive study for future study and development toward meeting the water-related needs of residents with the St. Vrain Basin
• Publications - Doc Type: Brochure

Page 4

In the agricultural sector, based on estimated full irrigation
water requi rements, a deficiency in avai lable supply present Iy exists in the
range of about 70,000 to 140,000 ac-ft/yr, depending on hydrologic conditions,
crop pattern, and growing season weather. Because of conversion of agricul-
tural land to urban-type uses, this deficiency in agricultural water supply is
forecast to deel ine to about 78,000 ac-ft in the year 2020 under a planned
target of providing 85% of the calculated Blaney-Criddle requirement during a
one in 10-year drought condition. This forecast assumes no further develop-
ment of the Basin's water resources for agriculture, but with improved overal I
irrigation efficiency from the presently estimated 45% to 50%. Agricultural
water requirements as presented herein are not to be construed as an economic
demand for water, since the cost of providing new supplies to meet present and
projected defici ts appears to be great Iy in excess of the economic return of
such water in crop production. Instead, water requirements were calculated
based on the empirical Blaney-Criddle approach to meeting the physiological
water requirements of crops to provide full crop yields or slightly reduced
yields during droughts.

2. Potential Additional Water Resources Development

The Study finds that about 13,000 ac-ft/yr of addi tional native
St. Vrain Creek water can be developed under a junior water right as firm
supply for M&I purposes. The storage capacity required to develop this supply
under the M&I drought criterion adopted for this Study would be about
80,000 ae-ft. Estimated costs of constructing a reservoir of this capacity
would be relatively high for any sites within the Study Area. Consequently,
it is concluded that this water supply would be too costly for irrigated agri-
culture in the absence of significant subsidies.

The potential for development of large water supplies from ground
water is considered negligible, due to prevai ling geologic conditions in the
Basin and the tributary nature of shal low alluvial aquifers.

3. Hydroelectric Potential

The potential for developing a signi ficant amount of conventional
hydroelectric power to produce revenues that would appreciably offset the cost
of a water resources project does not exist due to limited streamflows. How-
ever, the potential may exist for a moderate sized pumped-storage peaking
power development to be economically competitive with alternatives, but the
Study did not thoroughly evaluate this potential. Further study would be nec-
essary to identify and compare a potential project in the St. Vrain Basin with
other potential pumped-storage projects in the region where such capacity
could be marketed.

4. Non-Structural Water Resource Management Measures

The Study has identified a large array of non-structural measures
that have considerable potential to increase efficiency of water use or to
reduce the level of demand. Incorporation of selected non-structural measures

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