An Integrated Approach Toward Sustainability via Groundwater Banking in the Southern Central Valley, California

Abstract

Intensive groundwater withdrawals in California have resulted in depletion of streams and aquifers in some regions. Agricultural managed aquifer recharge (Ag‐MAR) initiatives have recently been piloted in California to mitigate the effects of unsustainable groundwater withdrawals. These initiatives rely on capturing wet‐year water and spreading it on large areas of irrigated agricultural lands to enhance recharge to aquifers. While recharge studies typically consider local effects on aquifer storage, few studies have investigated Ag‐MAR benefits and challenges at a regional scale. Here we used the Integrated Water Flow Model, to evaluate how Ag‐MAR projects can affect streamflows, diversions, pumping, and unsaturated zone flows in the southern Central Valley, California. We further tested the sensitivity of three different spatial patterns of Ag‐MAR, each chosen based on different thresholds of soil suitability, on the hydrologic system. This study investigates how the distribution of Ag‐MAR lands benefit the regional groundwater system and other water balance components. The results suggest that Ag‐MAR benefits vary as a function of the location of Ag‐MAR lands. Stream‐aquifer interactions play a crucial factor in determining the ability to increase groundwater storage in overdrafted basins. The results also indicate that Ag‐MAR projects conducted during the November–April recharge season have implications for water rights outside of the Ag‐MAR season. If not properly monitored, Ag‐MAR can cause a rise of groundwater table into the root zone, negatively impacting sensitive crops. Our work also highlights the benefits of using an integrated hydrologic and management model to evaluate Ag‐MAR at a regional scale.

Can Managed Aquifer Recharge Mitigate the Groundwater Overdraft in California's Central Valley?

“…Kourakos et al (2019) studied the effect of MAR in SR‐3 using some of the SAGBI recharge areas, which range between 42 and 154 km 2 , whereas the potential recharge area we use in the entire SR‐3 is 704 km 2 . Ghasemizade et al (2019) conducted numerical experiments with MAR scenarios in SR‐18 with a recharge area ranging between 313 and 1,023 km 2 , which is roughly comparable with 1,660 km 2 of suitable recharge areas we identified in SR‐18. Although the SAGBI classification provides the best available information on the soil's MAR potential, we acknowledge that there are uncertainties associated with the representation of subsurface geologic structures that might not be well captured by SAGBI (Maples et al, 2019).…”

“…MAR has the potential to replenish aquifers, reduce land subsidence risk, increase drought resilience, and lower flood‐related risks (Chinnasamy et al, 2018; Hashemi et al, 2015; Niswonger et al, 2017; Ronayne et al, 2017; Scanlon et al, 2016). MAR studies in California and elsewhere conducted at the local and farm levels (e.g., Bachand et al, 2014; Dahlke et al, 2018; Ghasemizade et al, 2019; Kourakos et al, 2019) demonstrate the potential of such practices to be scalable to the basin level. Strategies for implementing MAR on a more widespread basis are currently under investigation by CDWR (2018b, 2019).…”

Increasing Groundwater Availability and Seasonal Base Flow Through Agricultural Managed Aquifer Recharge in an Irrigated Basin

“…Irrespective of the diversion amount for groundwater recharge considered in our simulations, about 34% of the recharged water remained in groundwater storage and about 66% returned to streams as base flow, indicating that Ag‐MAR has the potential to stabilize and locally recover aquifer levels while increasing streamflow during summer low flow periods and the amount of groundwater available for irrigation. Similar groundwater storage gains were found by Niswonger et al () (e.g., 26–29% depending on aquifer hydraulic conductivity) for large‐scale Ag‐MAR simulations in the Carson Valley, NV and Ghasemizade et al () for the eastern San Joaquin Valley, CA. Other large‐scale MAR modeling studies have seen lower gains in groundwater storage (e.g., Ronayne et al, ; Scherberg et al, ); however, most studies observed similar clear benefits of recharge for groundwater‐dependent ecosystems and instream flows.…”

“…Feedback mechanisms between recharge and crop water consumption, crop ET, and water consumption by natural vegetation from elevated soil moisture and groundwater levels could not be estimated in this study because the model does not support simulation of recharge through the root and unsaturated zone. Although such processes are important for enhancing ecosystem services of groundwater‐dependent ecosystems (Bolund & Hunhammar, ; Dillon et al, ; Eamus & Froend, ; Fisher, ), Niswonger et al (), Wu et al (), and Ghasemizade et al () showed that the effect of recharge on crop water consumption and crop ET is modest (e.g., 3–6% increase in crop water consumption over the simulation period; Niswonger et al, ), but the increase in ET by natural vegetation can be significant (e.g., 20–30%; Niswonger et al, ) depending on soil moisture content.…”

Effects of upscaling temporal resolution of groundwater flow and transport boundary conditions on the performance of nitrate-transport models at the regional management scale

“…The third scenario is "winter recharge" (WR) which provides additional volume of water to farmlands during winter months of wet years. This scenario is also called agricultural managed aquifer recharge (Ghasemizade et al 2019;Kourakos et al 2019;Niswonger et al 2017). It increases landscape recharge without increasing agricultural nitrate losses.…”