USGS Pennsylvania Water Science Center
Poster Presentation at the 2016 American Water Resources Assoc. Annual Conference, November 13-17, 2016, Orlando, Florida.
Mapping groundwater withdrawals from wells relative to water-resource metrics or management targets
Maps of groundwater withdrawals are useful for informing stakeholders about groundwater use and its spatial character. Common methods for illustrating groundwater withdrawal magnitudes at individual wells on a map include using color gradation for the well symbols (usually circles), using discrete symbol sizes for categories of pumping rate, or scaling symbol sizes proportional to pumping rate. The latter method directly utilizes our intuition that visually larger symbols correspond to larger quantities, in this case withdrawal. Building on this approach, we developed a method that ascribes a physical significance to the proportionality between withdrawals (i.e. long-term average pumping rate, in units of volume per time) and symbol areas (units of length squared) on the map. For example, the user-defined proportionality, called the depth-rate index (units of length per time), can be based on the groundwater recharge rate, and the resulting map displays withdrawal magnitudes relative to that recharge. For a constant withdrawal, the symbol area increases as the depth-rate index decreases. Further, the method illustrates composite ‘symbols’, or ‘footprints’ for closely spaced wells, so that the combined withdrawal from a group of wells is equitably displayed relative to other, isolated, wells.
We implemented this method in a graphical user interface that facilitates input, algorithm execution, and map display of computed withdrawal footprints. The minimum data required are well locations and withdrawal rates, and the depth-rate index defined over a rectangular computational and display grid of uniform square cells. We demonstrate application of this new tool for several examples that visualize on maps the magnitudes of well withdrawals relative to depth-rate indexes corresponding to recharge, stream baseflow, water-table decline rates, and areal allocation limits.
In addition to illustrating withdrawal rates used as input to groundwater-flow or water-budget models, the footprint map may help increase stakeholder awareness about withdrawal rates in relation to water-resource metrics or to management limits. The footprints only visualize the magnitudes of withdrawal as areas spatially distributed around wells, and do NOT represent capture zones or recharge source areas for those withdrawals. Used as a screening tool, the footprint map may help identify areas where withdrawals are large, relative to the depth-rate index, and where groundwater modeling and other advanced methods of analysis may be warranted to characterize the impact of withdrawals on groundwater levels (storage), flow directions, and inflows to and discharge from the aquifer system.
Goode, D.J., and Winston, R.B., 2016, Mapping groundwater withdrawals from wells relative to water-resource metrics or management targets (abs.): 2016 American Water Resources Assoc. Annual Conference, November 13-17, 2016, Orlando, Florida. [http://pa.water.usgs.gov/projects/frhr/goode.winston.2016.php]
Also see Hydrogeology Journal article by Goode (2016).
Also see facsimile of slides from Technology Lightning Talk at the conference.