Numerical Ground‐Water Flow Modeling of the Snake River Plain Aquifer Using the Superposition Technique

Abstract

Predictive ground‐water flow modeling may be simplified by application of superposition when the governing equations are linear. The simplification allows evaluation of impacts of individual aquifer stresses and minimized model input, output, and interpretation. Modeling is performed by using (1) boundary conditions and aquifer properties provided by previous calibrations or analytical techniques, (2) setting the initial potentiometric surface and prescribed‐head boundaries to an arbitrary horizontal datum, and (3) simulating a specific recharge or discharge stress. Superposition was applied to an existing, calibrated model of the Snake River Plain aquifer to simplify prediction of changes in interaction with the Snake River. Simulations predict the temporal relationships between ground‐water use at multiple locations within the Snake River Plain and surface‐water depletion in four hydraulically connected reaches of the Snake River. Simulated aquifer water use at a location approximately five miles from a hydraulically connected river reach results in river depletions greater than 80% of the pumping rate after 10 years. Water use further than 50 miles from hydraulically connected river reaches results in depletions from 10 to 30% of the annual average pumping rate after 100 years. Results present spatial and temporal impacts of water uses on the Plain that are conceptually and quantitatively beneficial to water resources planners and water users.

A System Dynamics Model for Conjunctive Management of Water Resources in the Snake River Basin

“…One method that has been used to dynamically represent groundwater and surface water interactions is to add response functions generated from the groundwater model to the surface water planning model as was done by Miller et al (2003) for the Snake River Basin Model (SRBM) operated by the U.S. Bureau of Reclamation (USBR) (USBR, 2000). A response function is determined by stressing the groundwater model with a specified stress at a given location and then calculating response factors over a period of years to determine how that stress at a specific location impacts exchanges between the aquifer and various river reaches (Hubbell et al, 1997;Cosgrove and Johnson, 2004).…”

“…() for the Snake River Basin Model (SRBM) operated by the U.S. Bureau of Reclamation (USBR) (USBR, ). A response function is determined by stressing the groundwater model with a specified stress at a given location and then calculating response factors over a period of years to determine how that stress at a specific location impacts exchanges between the aquifer and various river reaches (Hubbell et al ., ; Cosgrove and Johnson, ).…”

REGIONAL SCALE MODELING OF SURFACE AND GROUND WATER INTERACTION IN THE SNAKE RIVER BASIN1

“…The effects are distributed among river reaches that are interconnected with the aquifer and other head dependent features. If the river, aquifer, and other system elements behave in a linear fashion, then the effects of multiple stresses at different times and locations are additive (Reilly et al, 1987;Hubbell et al, 1997). The MODSIM representation of surface and ground water interaction relies on this assumption of linearity.…”

RECHARGE OF THE SNAKE RWER PLAIN AQUIFER: TRANSITIONING FROM INCIDENTAL TO MANAGED1

“…Recharge in areas distant from springs will have a less immediate and more widely distributed effect on spring flows than recharge within a few miles of any given set of springs. A numerical modeling analysis employing superposition concepts was applied by Johnson et al (1993) and Hubbell et al (1997) to evaluate impacts of pumping at multiple locations in the Snake River Plain aquifer on spring discharge. The effects of recharge can also be inferred from those results.…”