Dynamic Simulation of Reclamation's Surface-Water Operations in MODFLOW-Based Hydrologic Models
Interaction between groundwater and surface-water, including stream depletions caused by groundwater
pumping, affects water supply and operations of Reclamation projects throughout the West. Current planning and
operations models represent groundwater/surface-water interactions using a variety of simplified approaches
ranging from specified inputs (e.g., fixed gains or losses) to simple analytical methods (e.g., unit response
functions). In many cases, these approaches do not accurately represent system behavior, resulting in significant
limitations for operations and planning studies. Moreover, these approaches are generally not well suited to
long-term planning studies that consider effects of climate change.
To address these limitations, Reclamation, in collaboration with USGS, recently developed a new surface water
operations model for the USGS Three-Dimensional Groundwater Flow Modeling Software (MODFLOW). This
module was developed in support of analysis and planning for the Rio Grande Project, located in southern New
Mexico and western Texas. The module was successfully used to simulate Rio Grande Project operations and
interactions between Project operations and local groundwater pumping for supplemental irrigation. However, the
existing surface water operations module is tailored to the Rio Grande Project and therefore not applicable to
other basins and other Reclamation projects.
This proposal seeks to expand and generalize the recently developed surface water operations module developed
for MODFLOW to allow analysis of other basins where conjunctive use and groundwater/surface water interactions
affect on Reclamation projects. The resulting module will be incorporated into the next official release of
MODFLOW-OWHM, the newest version of the MODFLOW software platform.
Need and Benefit
Stream depletions caused by groundwater pumping affect surface water supplies to Reclamation projects
throughout the West. In addition, groundwater/surface water interactions impact conveyance efficiency between
reservoir releases and diversion locations. The proposed surface water operations module for MODFLOW will
facilitate detailed analysis of stream depletions, their effects on Reclamation project supplies and deliveries, and
analysis of conjunctive management strategies to optimize surface water and groundwater use within a given
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