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

I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I

Page 3

reasonably be considered as anci Ilary features of plans formulated primari Iy
for water supply purposes.

In Step 2, preliminary alternative water resource management plans
were formulated by combining selected non-structural and structural elements
to meet various target levels of water supply development. Some 98 structural
elements and 26 non-structural elements were identi fied and evaluated on a
prel iminary basis. By combining various elements, ten prel iminary alternative
plans were formulated, of which six were subsequently evaluated. A computer-
ized River Basin Simulation Model was used as a tool in analyzing the antici-
pated performance of the formulated plans.

D. Findings and Conclusions

1. Water Supply and Demand

Native surface water resources in the Study Area average about
118,000 ac-ft/yr as represented by the combined runoff of St. Vrain and left
Hand creeks where they enter the plains from the foothi lis zone. Imported
water via the Colorado-Big Thompson Project has averaged about 31,000 ac-ft/yr
since the latter 1950's. Ground water usage and potential are I imi ted, and
the present use of this resource is estimated to be about g,ooo ac-ft/yr.

For the municipal and industrial (M&I) sector, population and
industrial growth are expected to result in increased water demand in the
Study Area from about 18,000 ac-ft/yr presently to about 44,000 ac-ft/yr in
2020 under a medium population growth scenario for drought year conditions.
The present fi rm annual water supply in the M&I sector is estimated to be
about 18,000 ac-ft. If no further supplies are developed and demand-reduction
measures are not implemented, the deficiency in year 2020 would be about
26,000 ac-ft/yr of firm supply. longmont's entitlement to 8,000 ac-ft of
Windy Gap Project supply could be uti lized to partially satisfy this deficit.

If this entitlement to Windy Gap Project supply is uti lized within
the Basin, not considering the potential for reuse, it is estimated that an
adequate drought-year supply wi II be avai lable for M&I purposes unti I some
point in the decade of year 2000 to 2010, assuming suitable cooperative
arrangements are consummated to ensure distribution of supplies to all users.
However, in the absence of further water resource development beyond utiliza-
tion of the Windy Gap supply and conversion of agricultural water rights on
urbanized lands to M&I use, drought-year supply capacity for M&I purposes
would be inadequate by about 18,000 ac-ft/yr in 2020 for a medium population
growth scenario. The Study placed considerable emphasis on identifying and
evaluating measures to reduce municipal water demand, both in average hydro-
logic years and in drought conditions. The Study adopted a criterion of pro-
viding capacity for M&I water supply in combination with demand reduction
sufficient to meet conditions anticipated during a 1 in 30-year drought.
Plans developed by the Study identify and evaluate alternative means for meet-
ing the projected M&I supply deficiency.