Comparing Streamflow Depletion Estimation Approaches in a Heavily Stressed, Conjunctively Managed Aquifer

Abstract

Estimating reductions in streamflow caused by groundwater pumping (“streamflow depletion”) is critical for conjunctive groundwater‐surface water management. Streamflow depletion can be quantified using analytical models, which have low data requirements but many simplifying assumptions, or numerical models, which represent physical processes more realistically but have high data, effort, and expertise requirements. Analytical depletion functions are a new tool that address some of the limitations of analytical models, but to date have only been evaluated in limited hydrogeological settings. Here, we compare eight different analytical depletion functions to streamflow depletion estimates from a calibrated MODFLOW numerical model used for conjunctive water management in the heavily stressed Republican River region of the High Plains Aquifer (USA). We find mostly strong agreement between the analytical depletion functions and the numerical model, though analytical depletion function estimates of depletion are lower for wells close to surface water features in high transmissivity settings. Compared to previous work, there is little variability among the eight analytical depletion functions, indicating that function formulation plays a minor role in this domain. Agreement between the modeling approaches is strongly influenced by hydrostratigraphic parameters (i.e., aquifer storage and transmissivity), suggesting accurate subsurface data are essential to estimating streamflow depletion regardless of modeling approach. Additionally, agreement between the two approaches is insensitive to pumping rate, confirming a key assumption of analytical models. Overall, analytical depletion functions provide comparable estimates of streamflow depletion to numerical models at a fraction of the time and data requirements.

Quantifying Streamflow Depletion from Groundwater Pumping: A Practical Review of Past and Emerging Approaches for Water Management

“…Recently, analytical depletion functions were proposed as an empirical tool to overcome the assumptions of a linear stream by accounting for multiple affected stream reaches and stream sinuosity (Zipper, Dallemagne, et al. 2018; Zipper, Gleeson, et al., 2019, 2021; Li et al. 2020, 2021).…”

“…Typically, models are developed for a region of interest (such as an aquifer or a watershed), a process that includes considerable data collection, database management, model construction, history matching, and visualization. Streamflow depletion is estimated by comparing streamflow in simulations with and without pumping in all or a subset of the domain (Hill et al 1992;Neupauer and Griebling 2012;Ahlfeld et al 2016;Zipper, Gleeson, et al 2021). Most streamflow depletion studies based on numerical models have used groundwater flow models such as MODFLOW, but recent examples have included integrated hydrologic models that couple land surface, vadose zone, and groundwater processes to simulate feedbacks between pumping, groundwater recharge, subsurface storage, and streamflow Maxwell 2014, 2019;Woolfenden and Nishikawa 2014;Kollet et al 2017).…”

“…The original 1943 Republican River Compact allocated the distribution of water among subbasins in each of the three states, but did not explicitly address how to account for streamflow depletion caused by groundwater pumping. Following a U.S. Supreme Court settlement between Kansas, Nebraska and Colorado, the interstate compact was modified to account for streamflow depletion due to groundwater extraction, which is quantified using the groundwater flow model jointly developed by the three states and federal government (RRCA 2003;Zipper, Gleeson, et al 2021). Each year, the states submit estimates of water supply and use, jointly evaluate the results of water accounting, update the MODFLOW model to estimate groundwater consumptive use and streamflow depletion across the basin, and assess compliance with the terms of the Republican River compact and legal settlements.…”

Quantifying Streamflow Depletion from Groundwater Pumping: A Practical Review of Past and Emerging Approaches for Water Management

“…Typically, models are developed for a region of interest (such as an aquifer or a watershed), a process that includes considerable data collection, data base management, model construction, history matching, and visualization. Streamflow depletion is estimated by comparing flow in surface water features in simulations with and without pumping in all or a subset of the domain (Ahlfeld et al, 2016;Hill et al, 1992;Neupauer and Griebling, 2012;Zipper, Gleeson, et al, 2021). Most streamflow depletion studies based on numerical models have used groundwater flow models such as MODFLOW, but recent examples have included integrated hydrologic models that couple land surface, vadose zone, and groundwater processes to simulate feedbacks between pumping, groundwater recharge, subsurface storage, and streamflow Maxwell, 2014, 2019;Woolfenden and Nishikawa, 2014;Kollet et al, 2017).…”

“…original 1943 Republican River Compact allocated the distribution of water among subbasins in each of the three states, but did not explicitly address how to account for streamflow depletion caused by groundwater pumping. Following a U.S. Supreme Court settlement between Kansas, Nebraska and Colorado, the interstate compact was modified to account for streamflow depletion due to groundwater extraction, which is quantified using the groundwater flow model jointly developed by the three states and federal government(RRCA, 2003;Zipper, Gleeson, et al, 2021). Each year, the states submit estimates of water supply and use, jointly evaluate the results of water accounting, update the MODFLOW model to estimate groundwater consumptive use and streamflow depletion across the basin, and assess compliance with the terms of the Republican River compact and legal settlements.…”