David R. Steward

Tapping unsustainable groundwater stores for agricultural production in the High Plains Aquifer of Kansas, projections to 2110

Significance Society faces the multifaceted crossroads dilemma of sustainably balancing today’s livelihood with future resource needs. Currently, agriculture is tapping the High Plains Aquifer beyond natural replenishment rates to grow irrigated crops and livestock that augment global food stocks, and science-based information is needed to guide choices. We present new methods to project trends in groundwater pumping and irrigated corn and cattle production. Although production declines are inevitable, scenario analysis substantiates the impacts of increasing near-term water savings, which would extend the usable lifetime of the aquifer, increase net production, and generate a less dramatic production decline. Groundwater provides a reliable tap to sustain agricultural production, yet persistent aquifer depletion threatens future sustainability. The High Plains Aquifer supplies 30% of the nation’s irrigated groundwater, and the Kansas portion supports the congressional district with the highest market value for agriculture in the nation. We project groundwater declines to assess when the study area might run out of water, and comprehensively forecast the impacts of reduced pumping on corn and cattle production. So far, 30% of the groundwater has been pumped and another 39% will be depleted over the next 50 y given existing trends. Recharge supplies 15% of current pumping and would take an average of 500–1,300 y to completely refill a depleted aquifer. Significant declines in the region’s pumping rates will occur over the next 15–20 y given current trends, yet irrigated agricultural production might increase through 2040 because of projected increases in water use efficiencies in corn production. Water use reductions of 20% today would cut agricultural production to the levels of 15–20 y ago, the time of peak agricultural production would extend to the 2070s, and production beyond 2070 would significantly exceed that projected without reduced pumping. Scenarios evaluate incremental reductions of current pumping by 20–80%, the latter rate approaching natural recharge. Findings substantiate that saving more water today would result in increased net production due to projected future increases in crop water use efficiencies. Society has an opportunity now to make changes with tremendous implications for future sustainability and livability.

Gaining and losing sections of horizontal wells

The flux along a horizontal well in uniform flow is examined using an analytic three-dimensional, steady model. Wells with uniform head and low pumping rates have gaining sections along which water enters the well and losing sections along which water exits. Such a well may provide a conduit for contaminated groundwater to be drawn into the well, conveyed a large distance, and injected into an uncontaminated region of an aquifer. Dimensionless ratios of the wells length L and radius R, aquifer thickness H, and uniform flow rate U are developed to quantify the minimum pumping rate Qmin at which no losing section occurs. The ratio Qmin/(ULH) is presented as a nomograph usingR/H and L/H for placement parallel to flow and is 6πR/H for placement perpendicular to flow, and a parabolic relationship between these limiting cases is developed for placement oblique to flow. Capture zone geometry is quantified using Qmin/(ULH).

The Simple Script Wrapper for OpenMI

Integrated environmental modeling enables the development of comprehensive simulations by compositing individual models within and across disciplines. The Simple Script Wrapper (SSW), developed here, provides a foundation for model linkages and integrated studies. The Open Modeling Interface (OpenMI) enables model integration but it is challenging to incorporate scripting languages commonly used for modeling and analysis such as MATLAB, Scilab, and Python. We have developed a general-purpose software component for the OpenMI that simplifies the linking of scripted models to other components. Our solution enables scientists to easily make their scripting language code linkable to OpenMI-compliant models fostering collaborative, interdisciplinary integrated modeling. The simplicity afforded by our solution is presented in a case study set in the context of irrigated agriculture. The software is available online as supplementary material and includes an example that may be followed to employ our methods.

A distributed data component for the Open Modeling Interface

As the volume of collected data continues to increase in the environmental sciences, so too does the need for effective means for accessing those data. We have developed an Open Modeling Interface (OpenMI) data component that retrieves input data for model components from environmental information systems and delivers output data to those systems. The adoption of standards for both model component input–output interfaces and web services make it possible for the component to be reconfigured for use with different linked models and various online systems. The data component employs three techniques tailored to the unique design of the OpenMI that enable efficient operation: caching, prefetching, and buffering, making it capable of scaling to large numbers of simultaneous simulations executing on a computational grid. We present the design of the component, an evaluation of its performance, and a case study demonstrating how it can be incorporated into modeling studies.

The Analytic Element Method and supporting GIS geodatabase model

This manuscript presents an overview of the Analytic Element Method, and illustrates how this mathematical technique is ideally suited to utilization within a GIS geodatabase model. The Analytic Element Method contains a set of analytic elements that exactly satisfy the governing partial differential equation and represent flow associated with a point, line or polygon. Elements are superimposed to simulate local and regional flow within an infinite domain. A GIS geodatabase model is presented here, which organizes spatial data in a vector format that relates directly to analytic elements. Scripts have been developed to automate the creation of groundwater models from the GIS geodatabase using the computer model MLAEM (Multi-Layer Analytic Element Model). An example is presented to illustrate the efficacy of this approach.

Analytic techniques for three-dimensional steady flow with two-dimensional and axisymmetric components

Publisher Summary Two-dimensional flow is the special class of flow that occurs in a plane and is symmetric in the direction normal to this plane. Axisymmetric flow is the special class of flow that occurs in half-planes containing an axis of symmetry and is symmetric about this axis. For many important applications, 3D flow may be decomposed into 2D and axisymmetric components. Irrotational flow fields are commonly analyzed using a potential function. These potentials may be added together to model any 3D flow that can be decomposed into two-dimensional and axisymmetric components. Divergence-free flow fields are commonly analyzed using the Lagrange stream function for 2D flow fields. While Lagrange and Stokes stream functions cannot be immediately added together as with the potential, it is shown that they may be combined through use of a vector potential. The vector potential is advantageous for computing flux, since dimensionality is reduced from the surface integral required to evaluate this flux using the specific discharge vector to a line integral. Computing flux using a vector potential is also advantageous for a flow field with 2D and axisymmetric components, since a method to obtain closed-form solutions exists in Steward for flux through surfaces bounded by straight line segments with arbitrary orientations.