Challenges of Managing Water Resources with Numerical Flow Models
ABSTRACT
Managing groundwater resources requires assessing effects of proposed changes on existing water rights tied to resources such as diversions, springs, and streams. Proposed changes historically have been simulated with analytical models, such as Theis and Glover solutions that estimate drawdowns, spring capture, and stream capture. These analytical solutions are limited to simple, homogeneous aquifers of infinite extent with non-existent or unrealistically simplified representations of springs and streams. Results from analytical models consistently diminish pumping effects as pumping moves further from a diversion, spring, or stream. Analytical model results are understood readily, require little explanation, and are wrong more frequently as distances between proposed pumping and existing resource increase. This is because significant aquifer heterogeneity more likely will be encountered as distances increase.
Numerical flow models are better than analytical models for assessing effects of proposed changes, because heterogeneous aquifers and complex interactions with springs and streams can be simulated. Advantages of numerical flow models also introduce more administrative challenges, because results are not always intuitively obvious as results from analytical models. Reasonableness of numerical flow-model results must be demonstrated with calibration criteria, where plausibility increases as simulated results better match as many relevant observations and concepts as possible. Advantages and challenges of assessing effects of proposed pumping changes will be illustrated with an example from the Amargosa Desert in southern Nevada.