A New Capture Fraction Method to Map How Pumpage Affects Surface Water Flow

Abstract

All groundwater pumped is balanced by removal of water somewhere, initially from storage in the aquifer and later from capture in the form of increase in recharge and decrease in discharge. Capture that results in a loss of water in streams, rivers, and wetlands now is a concern in many parts of the United States. Hydrologists commonly use analytical and numerical approaches to study temporal variations in sources of water to wells for select points of interest. Much can be learned about coupled surface/groundwater systems, however, by looking at the spatial distribution of theoretical capture for select times of interest. Development of maps of capture requires (1) a reasonably well-constructed transient or steady state model of an aquifer with head-dependent flow boundaries representing surface water features or evapotranspiration and (2) an automated procedure to run the model repeatedly and extract results, each time with a well in a different location. This paper presents new methods for simulating and mapping capture using three-dimensional groundwater flow models and presents examples from Arizona, Oregon, and Michigan.

Evaluation of Bias Associated with Capture Maps Derived from Nonlinear Groundwater Flow Models

“…The method used to compute capture fractions and generate capture maps using a groundwater flow model have been discussed by Leake et al (); however, new methodology and terminology are presented to further explore difficulties associated with applying the principle of superposition to nonlinear models: Capture Difference Map , is a map derived from subtracting one capture map developed using a high pumping rate from another developed using a low pumping rate. Capture Map Bias , is defined as the over‐ or underestimation of capture using capture maps derived from nonlinear groundwater flow models. Bias in pumping‐induced storage depletion also is included here. Capture Map Derived Capture (CMDC) , is defined as capture determined for a select group of wells using capture map methods developed by Leake et al (). …”

“…Capture maps for the hypothetical stream‐aquifer system are produced for five different pumping rates: 250 ft 3 /d, 750 ft 3 /d, 1250 ft 3 /d, 1900 ft 3 /d, and 2500 ft 3 /d (7 m 3 /d, 21 m 3 /d, 35 m 3 /d, 54 m 3 /d, and 71 m 3 /d) using the methods described by Leake et al (). Capture maps are developed by contouring capture fractions for a well pumping individually in each of the 3000 model grid cells.…”

“…Capture, as first described by Theis (1940), is the change in inflow to or outflow from a groundwater system caused by groundwater pumping. Numerous studies have revisited and expanded upon the concept of capture (Bredehoeft et al 1982;Leake et al 2008;Leake et al 2010; Barlow and Leake 2012;Davids and Mehl 2014;Konikow and Leake 2014). At the onset of pumping, water is removed from storage as drawdown surrounding the well (the cone of depression) extends outward.…”

Application of Hydrologic Tools and Monitoring to Support Managed Aquifer Recharge Decision Making in the Upper San Pedro River, Arizona, USA

“…Leake and others [49] provide detailed steps for developing a capture map using a groundwater model. Alternatively, capture for a given location can be calculated as the pumping time needed to reach a depletion-dominated supply (the time at which capture begins to provide greater than 50% of total groundwater pumped).…”

Capture-Rates and Directions of Groundwater Flow Don't Matter!

“…Reilly et al (1987) give examples of application of superposition methods in mildly nonlinear systems. For more discussion of effects of nonlinearities on capture, see Leake et al (2010).…”