Groundwater Pumping Impacts on Real Stream Networks: Testing the Performance of Simple Management Tools

Abstract

Quantifying reductions in streamflow due to groundwater pumping (“streamflow depletion”) is essential for conjunctive management of groundwater and surface water resources. Analytical models are widely used to estimate streamflow depletion but include potentially problematic assumptions such as simplified stream‐aquifer geometry and rely on largely untested depletion apportionment equations to distribute depletion from a well among different stream reaches. Here, we use archetypal numerical models to evaluate the sensitivity of five depletion apportionment equations to stream networks with varying drainage densities, topographic relief, and groundwater recharge rates; and statistically evaluate the sources of error for each equation. We introduce a new depletion apportionment equation called web squared which considers stream network geometry, and find that it performs the best under most conditions tested. For all depletion apportionment equations, performance decreases with increases in drainage density, relief, or recharge rates, and all equations struggle to estimate depletion in short stream reaches. Poorly performing apportionment equations tend to underestimate streamflow depletion relative to numerical model results, leading to a negative bias and underpredicted variability, while error in the best performing apportionment equations tends to be due to imperfect correlation. From a management perspective, apportionment equations with error due to bias and variability are preferable as they correctly identify which reaches will be affected and can be statistically corrected. Overall, these results indicate that the web squared method introduced here, which explicitly considers stream geometry, performs the best over a range of real‐world conditions, and will be most accurate in flatter and drier environments.

Rapid and Accurate Estimates of Streamflow Depletion Caused by Groundwater Pumping Using Analytical Depletion Functions

“…Finally, there is a negative correlation between analytical depletion function performance (normalized MAE) and stream segment length for stream segments <1 km in length, while performance is insensitive to stream segment length once segment length exceeds 1 km (Figure 9e). Poor performance in short streams was also observed under steady state conditions in Zipper, Dallemagne, et al (2018).…”

“…We evaluated the same five depletion apportionment equations as Zipper, Dallemagne, et al (2018). We briefly described them here (Figure 1, Step 2):…”

“…Water Resources Research types of error are discussed in Zipper, Dallemagne, et al (2018); having a relatively balanced error profile between variability and correlation indicates that both the overall mean depletion and the spatial patterns of depletion will be captured by the analytical depletion function.…”

The Demographics of Water: A Review of Water Ages in the Critical Zone

“…Aquifer areas range from several square kilometers up to several millions of square kilometers (BGR/UNESCO, 2008), and their permeability spans more than 12 orders of magnitude (Huscroft et al, 2018). If not influenced by groundwater extraction and not discharged directly into the oceans (e.g., Taniguchi et al, 2002), groundwater will eventually reach the land surface, either reentering the atmospheric cycle through root water uptake (Fan et al, 2017), discharging into lakes or wetlands (Ala-aho et al, 2015;Kluge et al, 2012), or providing the base flow that feeds streams during dry periods (Cuthbert, 2014;Zipper et al, 2018).…”

Streamflow depletion estimation for conjunctive water management in a heavily-stressed aquifer using analytical depletion functions

“…relative to the web equation is due to a negative bias for wells with high amounts of total 493 streamflow depletion (Table 1; Figure S10). This is caused by the increased weight given to 494 near-well stream segments in the web squared approach (Zipper et al 2018a). 495…”