Resources Assessment and
Water Rights Adjudication
Navajo Nation, Arizona
Development of groundwater resources for Indian Tribes
in the West revolve around Winters Doctrine rights
and the McCarran Amendment, which established Practical
Irrigable Acreage (PIA) as the yardstick to quantify
water rights. PIA claims are a complex interrelationship
among economic, hydrogeologic, market, agricultural,
and social factors. The hydrogeologic challenge is
to work closely with tribal leaders, economists, agronomists,
and soil scientists to jointly develop appropriately
scaled and economically viable irrigation projects.
We were retained to conduct several groundwater resource
assessments and impact studies within the Little Colorado
River Basin of Arizona, a 27,000 square mile watershed.
The development of groundwater resources from aquifers
in the Dakota, Navajo, and Coconino Sandstones was
to be investigated. Optimal resource development scenarios
required working closely and interactively with the
economists and agricultural specialists.
Investigation and Results
A largescale hydrogeologic and geochemical field
investigation was conducted throughout the Basin.
The investigation included geologic mapping, inventorying
springs and wells, aquifer testing, and geochemical
and isotopic sampling and interpretation. Analytical
and numerical models were developed to evaluate groundwater
response to proposed agricultural and Tribal water
supply developments. Basinwide numerical models
were developed of all three major aquifer systems
to evaluate such diverse goals as sustainable development
and impact on spring discharges in the Grand Canyon
and other critical habitats. More than 20 project
reports describe the results and interpretations of
the various tasks. We are providing continuing expert
witness support in the adjudication process. Completed
Numerical simulation and water quality evaluation
of a proposed agricultural development using brackish
to moderately saline water.
Prediction of impacts of industrial groundwater
developments (power plants) on groundwater resources,
spring flow, and stream flow.
Basinwide isotopic assessment including
recharge and groundwater age determinations.
Projections of the impacts of population changes
on Tribal lands on Tribal water resources.
Development of an agricultural wellfield cost
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