[Illustration: A cross section through the Front Range northwest of
Denver shows the redistribution and use of western slope water in
eastern Colorado through the Colorado-Big Thompson Project. This project
has cost about $160,000,000, but it is repaying the investment many
times over by providing electric power and increasing farm production.]
Moisture carried by prevailing westerly or northwesterly winds falls
primarily on Colorado’s western slope, although at some times of year
precipitation may come from the northeast or southeast. West of the
continental divide, where population is sparse, there is a surplus of
water. East of the divide, where more than 90 per cent of the population
lives, water is in desperately short supply. The high and largely
unpopulated Mountain Province receives by far the greatest proportion of
precipitation, while agricultural areas of the Prairie and Plateau
Provinces receive much less. Needless to say, the major problem
involving water in Colorado is how to move it from areas where it is
abundant to areas where it is needed.
In many parts of the state, complex water laws and complicated
irrigation canals and water systems were developed soon after the area
became settled. Gradually but inevitably, water resources have been
transferred from the western slope to the eastern. However, such
transfer must be undertaken with due regard for the rights of downstream
users, notably California, Arizona, and New Mexico.
One of the largest water movement schemes in the state is the
Colorado-Big Thompson Project. Water that otherwise would flow into the
Colorado River is piped from Grand Lake through the Alva B. Adams tunnel
under the high mountains of Rocky Mountain National Park, and into the
Big Thompson drainage near Estes Park. It then travels through a series
of reservoirs and tunnels into the South Platte River basin, where it is
used for irrigation and household water. The water is pumped up the
western gradient of this system by electric power produced as it flows
down the eastern slope. Surplus electric power serves the
Colorado-Wyoming area.
Another large project is the Denver Water Board’s Dillon Reservoir
Project, in which western slope water collected at Dillon is pumped
twenty-three miles under the continental divide through the Harold D.
Roberts tunnel to the North Fork of the South Platte River for use by
the city of Denver. The exit point of this tunnel can be seen a few
miles west of Grant along U. S. highway 285. This project is
continuously growing as Denver’s water needs mount.
In each of these projects, engineering geologists played a prominent
part in locating dams and tunnels that would not leak or fail, and that
could collect and transport a maximum amount of water during the
high-runoff spring season for distribution through the rest of the year.
Fortunately for geologists, the tunnels and bores necessary to the
projects allowed them to learn a great deal about the structure of the
interior of the high mountains, and helped to improve their
interpretation of earth history in this most interesting region.
The necessity for storing irrigation water along the eastern mountain
front has led to the creation of hundreds of new lakes in the region.
Although water levels vary with the season, many of the lakes provide
opportunities for water sports and recreation for the burgeoning inland
population.
Two large dams have recently been built in western Colorado for another
purpose: to control the flow of water in the Colorado River drainage
basin. Electric power for western Colorado also comes from these dams.
One of the dams is on the Gunnison River at Curecanti, upstream from the
Black Canyon of the Gunnison National Monument, and the other is on the
Frying Pan River near Ruedi. The latter was completed over the
objections of geologists, who believed that the extensive gypsum
deposits underlying the damsite would cause its failure. Cement pumped
deep into the rocks in the vicinity has so far prevented serious
rupture.
There is strong resistance by conservation groups to the construction of
more dams on Colorado River drainage, primarily because the Colorado and
its tributaries pass through many irreplaceable canyons, some of them
parts of National Parks and Monuments, that are very much a part of our
western heritage.