Ground-Water
Models of the Alluvial and Sparta Aquifers: Management Tools for a Sustainable
Resource
Abstract: Conjunctive-use optimization
modeling was done to assist water managers and planners by estimating the
maximum amount of ground water that hypothetically could be
withdrawn from wells within the Mississippi River Valley alluvial
and Sparta aquifers without violating hydraulic-head or
stream-discharge constraints. In 1997, nearly 6 million acre-feet of
water were pumped from the
aquifers by more than 45,000 wells, primarily for irrigation
and for fish farming. Several large cones of depression have
formed in the potentiometric
surface, resulting in lower well yields and degraded water
quality in some areas. MODFLOW-based ground-water flow
models were developed for the north and south
portions of the alluvial aquifer, primarily in eastern
Arkansas, and for the Sparta aquifer in Arkansas, Louisiana,
and Mississippi. MODMAN optimization models based on these flow
models showed that continued pumping
at 1997 rates are unsustainable without
violating head constraints imposed as a part of
Arkansas' Critical Ground-Water Area criteria. In
addition, streamflow constraints
were established based on minimum
flow requirements for maintaining water quality and fish
habitat. Preliminary results show that continuous
pumping at 1997 rates indefinitely resulted in water
levels dropping below the
hydraulic-head constraints, making these rates
unsustainable. Optimized sustainable pumping was obtained such that
water levels were maintained
at or above the hydraulic-head constraints, and streamflow
was maintained at or above minimum levels. Optimized sustainable yields from streams were nearly 2
orders of magnitude greater than for
ground water.
Biography: John Czarnecki is the ground-water
specialist at the U.S. Geological Survey District
office in Little Rock, Arkansas. Prior to coming to