A Proposed Approach to Sustainable Groundwater Extraction Based on Surface Water-Groundwater Interaction

Understanding the interaction of interconnected groundwater-surface water systems is fundamental to sustainable water resources management; however, surface and groundwater management decisions must address fundamentally different issues and time frames. Surface-water management must respond to short-term climatic variations, flood control, streamflow requirements, and changes in water demand and availability. Groundwater systems typically respond to recharge and extraction over decades or longer, requiring longer-term management decisions. We present an approach to groundwater management based on management zones that recognize the physics of surface water-groundwater interaction, but honors these inherently different management requirements. Examples are provided for the Stanislaus, Tuolumne, and Colorado Rivers in California.

The amount and timing of streamflow depletion depends on pumping rate and duration, well location relative to the stream, aquifer diffusivity, streambed conductance, and vertical flow impedance within the aquifer system. These principles were used to develop proposed groundwater management zones around aquifer-connected streams by simulating extraction from theoretical wells at various depths and distances from the streams, under a range of stream and aquifer conditions. Simulations were carried out using STRMDEPL08, an analytical streamflow-depletion model developed by the USGS, and validated using existing numerical groundwater flow models constructed using the USGS MODFLOW code. Simulated surface water depletion by shallow wells near streams closely mimics applied pumping rates and timing, which supports groundwater management in tandem with surface water as is currently done in California for pumping from a “known and definite channel.” Pumping from greater distance or depth causes an attenuated hydrologic response in both amplitude and time. Groundwater management zones are thus proposed based on distance to the affected stream, depth of the well’s screen interval, and timing and duration of predicted streamflow depletion, considering the amount of seasonal and long-term streamflow depletion that is tolerable under existing ecological and water rights requirements.