Evaluating the integration of water operations models with groundwater models
This project would fall under the demonstration of research category and would attempt to answer the question:
(1) can the recently integrated codes MODSIM and MODFLOW, which simulate river-reservoir operations and
groundwater and surface water flow as well as their inter-dependence, respectively, be used in a basin with
complex and competing operations to more accurately represent the nonlinear feedbacks between the operations
and the groundwater/surface water interactions resulting from those operations, and (2) does the new tool
improve the calibration quality of the river-reservoir model (MODSIM)?
Need and Benefit
Modeling groundwater/surface water interactions within regulated river systems is commonly ignored or
over-simplified, simply because combining the appropriate tools to simulate both regulated surface water and
groundwater systems has been too cumbersome (i.e., poor understanding of the respective source codes),
computationally intensive, or time consuming. MODSIM, originally authored at Colorado State University (CSU), is
offered to the public at no cost and falls within a genre of software codes providing functionality for simulating
complex river operations governed by water rights, administrative constraints, and agreements. Like many of the
codes that fall under the "river operations" umbrella, simulation of groundwater/surface-water interaction is
accomplished using simplified one-dimensional equations or estimated stream-depletion factors. These methods
are overly simplistic and fail to properly account for the influence of groundwater on streamflow in areas with
significant and transient groundwater pumping. MODSIM and MODFLOW are now coupled such that they reach a
converged solution for each time step by satisfying the water right rules that are constrained by water availability
simulated by MODFLOW. This type of coupling requires iteration during each time step, an important facet of the
MODSIM-MODFLOW integration tool that was not found anywhere in the scientific literature. Functionality provided
by the integration of MODSIM and MODFLOW is a perceived software need within the USGS and offers new
functionality for those analyzing water resources issues in developed basins. Conversely, MODFLOW (and by
extension, GSFLOW) offers a powerful modeling venue for quantifying the impacts of pumping on in-stream flows
simulated with the surface-water packages (e.g., SFR2, SWR) available within MODFLOW. However, MODFLOW lacks
basic functionality for simulating river operations subject to the legal framework governing the administration of
surface-water flows during model execution. This makes it difficult to accurately quantify and demonstrate the
impacts of groundwater pumping on river operations for guiding sound water management. In short, the
weakness of each modeling platform (MODFLOW and MODSIM) is complemented by the strength of the other.
Contact the Principal Investigator for information about partners.
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