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Water Supply Issues in Grasslands
Barbara Tellman, Panel Moderator3
INTRODUCTION TO THE SESSION
Water supply is crucial to grassland health. In arid regions, any depletion of water supply can
make the difference between a thriving grassland and an unhealthy system tending towards
dessication. In this session we will look at two studies of water supply in a healthy grassland
system in southern Arizona, the Patagonia-Elgin-Sonoita area. The area is southeast of Tucson,
Arizona, just north of the border with Sonora. The Audubon-Whittell Research Ranch is located in
this area, as are many other private thriving ranches. The area has been relatively stable for the
past one hundred years since Anglo settlement in the area took root. The area has had fewer
problems from overgrazing than most other parts of Arizona.
Over the past ten years urbanization has been creeping into the area. Since 1990, the impacts
of this urbanization have been a major concern for many ranchers. Impacts include change in fire
management regimes, changes in grassland composition as large ranches are broken up into
subdivisions, with ranchettes of 4 acres or less, and changes in the ability of wildlife to use the area
for corridors. Vineyards and other types of agriculture have increased greatly in recent years also.
One of the greatest concerns to managers of the Research Ranch and many others, is a threat
to the local water supply. Ranching uses relatively little water, compared to more urban uses.
Today we will look at two studies of water supplies in the area, as examples of how people in
rural areas can examine water supply problems and threats to determine what the impacts of
population growth will be in regard to water supply. But before looking at these studies, I will briefly
describe a water supply problem that occurred more than twenty years ago in the area and was
solved through the use of water supply data.
The areas where the BLM Empire-Cienega Conservation Area is today was once slated for a
major development of at least 50,000 people. The area had been owned by a mining company
who decided to sell to a land speculator for the purpose of established a planned community within
easy commuting distance of Tucson. A rezoning was necessary, complicated by the fact that the
land extends into two very different counties - Pima County and Santa Cruz County. The area is in
the upper reaches of the watershed from which Tucson (in Pima County) derives some of its surface
water supply.
Opposition to the rezoning was fierce in both counties, but the most heated battles were waged
before the Pima County Board of Supervisors. Among many arguments, opponents challenged the
availability of water for such a large community. There was no provision in Arizona water law that
would deny the rezoning, so the counties had to be convinced to deal with the issue through the
zoning process.
To make a very long story short, the rezoning was approved on a scaled down basis, with the
provision that construction could only proceed in phases, dependent on the developer proving the
availability of water. The burden was on the developer to do the necessary studies to prove longterm availability. A first phase was approved allowing for as many homes as could be supported on
the known water supply. If the developer could prove the existence of more water, he could then
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Water Resources Research Center, University of Arizona, Tucson AZ..
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proceed with phase two, and later other phases until full build-out. The developer did not find this
financially feasible and dropped the project. Thus, the land became available at a later date for a
publicly owned Conservation Area.
The two studies which follow discuss water supply for an area south of the one just described
They are instructive in terms of knowing what are the right questions to ask. Neither study was
very costly, but both are extremely useful to current residents.
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