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Evaluation of bias associated with capture maps derived from nonlinear groundwater flow models

September 28, 2017

The impact of groundwater withdrawal on surface water is a concern of water users and water managers, particularly in the arid western United States. Capture maps are useful tools to spatially assess the impact of groundwater pumping on water sources (e.g., streamflow depletion) and are being used more frequently for conjunctive management of surface water and groundwater. Capture maps have been derived using linear groundwater flow models and rely on the principle of superposition to demonstrate the effects of pumping in various locations on resources of interest. However, nonlinear models are often necessary to simulate head-dependent boundary conditions and unconfined aquifers. Capture maps developed using nonlinear models with the principle of superposition may over- or underestimate capture magnitude and spatial extent. This paper presents new methods for generating capture difference maps, which assess spatial effects of model nonlinearity on capture fraction sensitivity to pumping rate, and for calculating the bias associated with capture maps. The sensitivity of capture map bias to selected parameters related to model design and conceptualization for the arid western United States is explored. This study finds that the simulation of stream continuity, pumping rates, stream incision, well proximity to capture sources, aquifer hydraulic conductivity, and groundwater evapotranspiration extinction depth substantially affect capture map bias. Capture difference maps demonstrate that regions with large capture fraction differences are indicative of greater potential capture map bias. Understanding both spatial and temporal bias in capture maps derived from nonlinear groundwater flow models improves their utility and defensibility as conjunctive-use management tools.

Publication Year 2018
Title Evaluation of bias associated with capture maps derived from nonlinear groundwater flow models
DOI 10.1111/gwat.12597
Authors Cara A. Nadler, Kip K. Allander, Greg Pohll, Eric D. Morway, Ramon C. Naranjo, Justin Huntington
Publication Type Article
Publication Subtype Journal Article
Series Title Groundwater
Index ID 70191177
Record Source USGS Publications Warehouse
USGS Organization Nevada Water Science Center