CRWR Online Report 2000-8
The Effect of Time-Step Length in Modeling River and Aquifer Interaction
By Shiva Niazi, Randal Charbeneau, and David Maidment
ABSTRACT
In modeling groundwater and surface water systems simultaneously,
the issue of time-step length becomes paramount due to the difference in residence times of rivers
and aquifers. To determine the effect of time-step length in modeling river and aquifer systems, a
MODFLOW groundwater model of Milam, Lee and Bastrop counties was dynamically linked to a model of the
Colorado River. In a dynamic link between separate surface water and groundwater models, the output
of one model is used to update the input of the other model in a cyclic fashion. In this scenario,
time-step length is redefined as the length of time each model is allowed to run before updating the
other model. A series of 32-day flood wave simulations were performed to determine the effect of
averaging a highly fluctuating river discharge over progressively longer time-steps. The preliminary
results of this study suggest that time-step affects the quantity of water that the model predicts
is exchanged between the river and aquifer. However, these results were neither validated with
another coupled river and aquifer modeling system nor with field data gathered from groundwater
wells near the river
CRWR Online Report 2000-8
The Effect of Time-Step Length in Modeling River and Aquifer Interaction
By Shiva Niazi, Randal Charbeneau, and David Maidment
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