- Although surface water constitutes less than 1.5% of freshwater supply, historical development of surface water sources continues to mark the landscape. However, over- exploitation of groundwater is now at its highest, and 25% of the world’s 1.7 billion population live in water scare regions. As glaciers and snowpack disappear due to increasing temperatures, sea level will continue to decrease our access to freshwater sources. Since aquifers hold substantial groundwater, managed aquifer recharge (MAR) is a suite of strategies designed to enhance recharge for later development, including augmentation of stream flows. Mean global residence time of groundwater is estimated to exceed 250 years, while water maintained in above ground reservoirs has an average residence time of less than 4 years. By retaining surface water with MAR, enhanced recharge can increase surface water residence time, especially in locations where excess flows from glacial melt or snowpack degradation can be captured before it is no longer available.
The research presented here is a composition of various methods designed to assess MAR potential on different scales. Rooted in hydrogeological analyses, it is also very multidisciplinary, as it draws upon the fields of geology, engineering, spatial geography, water policy, and ecology. Research in MAR with a multidisciplinary approach is needed to enhance its global use, yet it is in its infancy as many locations lack groundwater data. With technological advances in geographical information systems, increased resolution of satellite imagery, and rapid data processing speeds, the boundary of our understanding of MAR potential on a spatial scale is being pushed at a considerable rate.
In this work, two types of MAR options were assessed - Aquifer Storage and Recovery (ASR), which injects and recovers water in the same well, and Shallow Aquifer Recharge (SAR), which recharges the aquifer through passive means. The following methods of analyzing suitability included, an ASR site scoring system, developed and applied on a regional and local scale in Washington, USA. This approach estimated that over 50% of 284 locations met the hydrogeological properties, regulatory influences, and operational considerations suitable for ASR.
The development of an ASR water well suitability analytical method was used to assess potential groundwater injection rates in Washington, USA. Estimation of suitability was based on pre-designated values. It was found that statewide potential equaled 6400 million liters per day. The creation of a Multi-Criteria Decision Analysis utilizing an Analytical Hierarchy Process and weighted overlay method was used to qualify SAR prospects in 6 sub-basins within the Yakima River watershed, Washington, USA. Results were coupled with analytical methods to approximate groundwater recharge rates. An analytical technique was also applied to estimate ASR potential within a principal confined aquifer. It was found that 0.1 to 5.9% of the land in the sub-basins are suitable for SAR. For ASR, it was estimated that the confined aquifer can support injection rates averaging 18,900 meters cubed per day.
The development of a System Dynamics Model of the Yakima River watershed (YAK-SDM) in Washington, USA was used for rapid data processing, enhanced policy scenario alternatives, and provided local and watershed-scale MAR potential against historical surface flow conditions that varied under climate-induced changes. It was found that available aquifer storage exceeded surface water potential predicted for recharge. Under adverse climate conditions, re-timing of recharge will need to occur earlier in the year to accommodate changes in runoff patterns. To properly understand local-scale MAR feasibility, ‘soft’ factors such as public perception and trust among stakeholders required consideration, as these factors can obstruct, dampen, or dismantle prospective projects. Therefore, the YAK-SDM was also constructed as a tool that quickly allowed for policy adaption based on quantitative scenarios housed in stakeholder collaboration through a mutual-gains lens to MAR development.