SIMULATED GROUND-WATER FLOW IN THE HUECO BOLSON, AN ALLUVIAL-BASIN AQUIFER
SYSTEM NEAR EL PASO, TEXAS  
(pdf file 5.5 Mb)

By Charles E. Heywood and Richard M. Yager



ABSTRACT

The neighboring cities of El Paso, Texas, and 
Ciudad Juarez, Chihuahua, Mexico, have historically 
relied on ground-water withdrawals from the Hueco 
Bolson, an alluvial-aquifer system, to supply water to 
their growing populations. By 1996, ground-water 
drawdown exceeded 60 meters in some areas under 
Ciudad Juarez and El Paso. 

A simulation of steady-state and transient 
ground-water flow in the Hueco Bolson in westernmost 
Texas, south-central New Mexico, and northern 
Chihuahua, Mexico, was developed using 
MODFLOW-96. The model is needed by El Paso 
Water Utilities to evaluate strategies for obtaining the 
most beneficial use of the Hueco Bolson aquifer 
system. The transient simulation represents a period of 
100 years beginning in 1903 and ending in 2002. The 
period 1903 through 1968 was represented with 66 
annual stress periods, and the period 1969 through 
2002 was represented with 408 monthly stress periods. 

The ground-water flow model was calibrated 
using MODFLOWP and UCODE. Parameter values 
representing aquifer properties and boundary 
conditions were adjusted through nonlinear regression 
in a transient-state simulation with 96 annual time steps 
to produce a model that approximated (1) 4,352 water 
levels measured in 292 wells from 1912 to 1995, (2) 
three seepage-loss rates from a reach of the Rio Grande 
during periods from 1979 to 1981, (3) three seepage-
loss rates from a reach of the Franklin Canal during 
periods from 1990 to 1992, and (4) 24 seepage rates 
into irrigation drains from 1961 to 1983. Once a 
calibrated model was obtained with MODFLOWP and 
UCODE, the optimal parameter set was used to create 
an equivalent MODFLOW-96 simulation with monthly 
temporal discretization to improve computations of 
seepage from the Rio Grande and to define the flow 
field for a chloride-transport simulation.

Model boundary conditions were modified at 
appropriate times during the simulation to represent 
changes in well pumpage, drainage of agricultural 
fields, and channel modifications of the Rio Grande. 
The model input was generated from geographic 
information system databases, which facilitated rapid 
model construction and enabled testing of several 
conceptualizations of hydrogeologic facies boundaries. 
Specific yield of unconfined layers and hydraulic 
conductance of Quaternary faults in the fluvial facies 
were the most sensitive model parameters, suggesting 
that ground-water flow is impeded across the fault 
planes.



Abstract from Water-Resources Investigations Report 02-4108