How Can Long-Term Water Storage Management Mitigate Problems in an Era of Water Resource Deficits?

Mengqi Zhao, Ph.D. Candidate, Department of Civil and Environmental Engineering, Washington State University

The 2015 drought caused more than $700 million in economic losses across Washington State. Even with current water storage management, both in places where rivers, lakes, and reservoirs generally provide sufficient water and in places where aquifers are the most stable water resource across seasons, extreme drought still impacted our economy. While droughts may impact different places with varying intensity, the risk of long-term water scarcity is greater when aquifers provide water today at the expense of tomorrow’s supply. As the region faces population increases and increasing competition for water resources to provide environmental value and economic value, the risk may increase further. So what water management options can help us mitigate the impacts of drought in the future?

In our region, we are experienced in using surface reservoirs as buffers between the naturally variable water cycle and the relatively more consistent agricultural water demand. The less visible buffer underground has often been ignored. Yet interest is growing, as aquifers may also be a useful reservoir over the long term, if managed sustainably. Our research team is evaluating managed aquifer recharge (MAR), an approach that stores water in the aquifer during the snowmelt season, allowing users to pump it for irrigation during periods of water scarcity (Figure 1). We have been asking questions about how to recharge aquifer systems to optimally achieve both short-term usage and long-term water supply sustainability. Imagine that the amount of water recharged into the aquifer becomes your future available MAR entitlement to pump up when needed. The more water that recharges the aquifer, the more effective the MAR will be in mitigating drought impacts. We are interested in answering specific questions, such as ‘What timing of recharge and infiltration area would have been needed for managed aquifer recharge to provide an effective buffer against the 2015 drought?’ or ‘How effective is managed aquifer recharge for maintaining sustainable water supply during single-year drought or even multi-year droughts?’

Our team developed a system dynamics model that aims to capture historical behaviors of where and how much water is being allocated (based on historical data), and then to help answer ‘what if’ questions. The model quantifies physical processes, including how water moves throughout the water cycle (on the surface, in the soil, and in the aquifer). It also represents key socio-economic factors from markets, social norms, and policies (supply and demand, innovation adoption, and water rights). We applied the model to the Yakima River Basin and compared calculated and observed streamflow data at the Parker gage station (below the City of Yakima) to verify whether or not it can capture downstream flow behaviors after reservoir operations seen in that Basin. With our verified model, the user-friendly interface of the system dynamics model enables managers to evaluate, for instance, how much water is needed and how much water is available for irrigation in August, if they decide to withdraw 20,000 acre- feet of water from the river to recharge the aquifer in February?

The model allows users to explore dynamic water allocations and water scarcity level on the fly by dragging sliders of different variables (Figure 2). For example, during the 2015 drought, the water available to proratable water right holders in the Yakima River Basin was only 47% of their full entitlements. Our model gives users the ability to evaluate scenarios exploring how much and when to recharge the aquifer, and to visualize how the reliability of irrigation water supply might improve in years like 2015.

Here is an example: Let’s see how different recharge decisions on infiltration areas affect irrigation supply during a drought like 2015’s. Assuming MAR had been implemented in 2006, we evaluated the impact of different infiltration area at 200, 300, and 400 acres on irrigation water supply (Figure 3). As we increased the infiltration area, more water could percolate through infiltration ponds and accumulate in the aquifer. During the drought, all the recharge scenarios we explored improved irrigation reliability when compared to the scenario without MAR implementation (compare Figure 3a to Figures 3b-d). We found that to fully alleviate the drought’s impacts, 337,000 acre-feet of recharged water needed to be pumped (see scenario 4, in Figure 3d).

As we gain greater understanding of the real-world particulars of MAR implementation in regions like the Yakima River Basin, we aim to improve the confidence in the model’s ability to represent aggregated and large-scale patterns that influence how water is managed across the Columbia River Basin. We welcome insights into the main features that characterize different regions across the basin that may influence the effectiveness of MAR under various drought scenarios.

This article was revised from the original version, titled “How Can Long-Term Water Storage Management Mitigate Problems in an Era of Resource Deficits?” published in November 2019 as part of the following report: Hall, S.A., Yorgey, G.G., Padowski, J.C., Adam, J.C. 2019. Food-Energy-Water: Innovations in Storage for Resilience in the Columbia River Basin. Progress Report for the Columbia River FEW Project. Available online at www.fewstorage.wsu.edu.

The work described in this article was supported jointly by the National Science Foundation under EAR grant #1639458 and the U.S. Department of Agriculture’s National Institute of Food and Agriculture under grant #2017- 67004-26131, as well as the Washington State University Graduate School.