Managed winter flooding of alfalfa recharges groundwater with minimal crop damage

Abstract

roundwater is a vital resource in California, providing approximately 38% of the state's water supply in normal years and at least 46% in dry years (DWR 2014). During the recent drought (water years 2011-2012 through 2015-2016), the majority of groundwater wells (90%) experienced a drop in groundwater levels of at least 10-50 ft (3-15 m) while some wells (8%) showed declines in groundwater level of more than 50 ft (>15 m) (DWR 2017). Groundwater overdraft persisted for most of the 20th century but the rate has dramatically increased since 2000 to about 7.2 million acre-feet (ac-ft), or 8.9 cubic kilometers (cu km) per year between 2006 and 2010 (Faunt 2009; Scanlon et al. 2012). State legislation now requires the implementation of groundwater sustainability plans to ensure that all groundwater basins are managed sustainably by 2040 (SWRCB 2014). Managed groundwater recharge on agricultural lands in winter, when surplus surface water often is available, is one promising strategy for replenishing RESEARCH ARTICLE Managed winter flooding of alfalfa recharges groundwater with minimal crop damage Over 90% of the water applied to sites in Davis and Scott Valley percolated to recharge groundwater, making this a viable practice on highly permeable soils.

Modeling managed aquifer recharge processes in a highly heterogeneous, semi-confined aquifer system

“…There is interest in expanding use of MAR in CA, both to offset overdraft and to hedge against future decreases in snowpack-water storage and changes in the timing and volume of surface-water availability. Established MAR projects commonly use dedicated infiltration basins located over locally coarse-texture geological deposits to increase recharge, but increasingly, MAR on agricultural fields during nongrowing seasons (Ag-MAR) has been proposed as an alternative to infiltration basins (Dahlke et al 2018;Harter and Dahlke 2014;Niswonger et al 2017). Studies have noted that even during periods of water scarcity, wet-season high-magnitude streamflows (HMF) can often provide ample unmanaged surface water for MAR during nongrowing seasons in CA (Beganskas and Fisher 2017;Kocis and Dahlke 2017) and elsewhere (Chinnasamy et al 2018).…”

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

“…Locations were further constrained by selecting sites with crops that are suitable for winter recharge. Only finite elements that had at least 50% of the area planted with alfalfa or almonds in 2014 were selected for Ag‐MAR, following suggestion by Dahlke, Brown, et al () and Bachand et al (, ). Land use was determined from the 2014 USDA NASS land use data (USDA National Agricultural Statistics Service Cropland Data Layer, ).…”

“…Methods to achieve sustainable management of groundwater resources range from conservation (i.e., reduced groundwater pumping), conjunctive use (substituting surface water for groundwater to reduce groundwater use), and in‐lieu recharge (supply surface water to users who normally use groundwater) to various managed aquifer recharge (MAR) methods, which intentionally place more water in groundwater aquifers than would otherwise naturally occur (Bouwer, ; Kocis & Dahlke, ; Scanlon et al, ). MAR approaches use a variety of water sources (e.g., river water: Scanlon et al, ; stormwater: Page et al, ; treated wastewater: Zekri et al, ; Bugan et al, ; or desalinated water: Kimrey, ) and methods (e.g., infiltration basins or channels, injection and recovery of groundwater through wells, induced bank filtration, off‐season spreading of water on farmland; Dahlke, Brown, et al, ; Dillon, ; Russo et al, ) to intentionally replenish underlying aquifers.…”

Domestic well vulnerability to drought duration and unsustainable groundwater management in California’s Central Valley

“…In California, high-magnitude flood flows are likely the most accessible and largest sources of water to replenish groundwater aquifers through managed aquifer recharge [59], which might considerably slow or reverse trends in groundwater depletion. The emerging research in the strategic siting of managed aquifer recharge considers impacts on crop health [60], human health [61], the mobilization of contaminants into groundwater [62], and hydrogeologic suitability (i.e.-highly conductive flowpaths and geologic formations capable of accommodating large volumes of water, such as incised valley fills) [63]. In the San Joaquin Valley where domestic well failures peak, managed aquifer recharge alone may not be enough to offset groundwater overdraft, but coupled with a reduction in agricultural water use [46], groundwater levels may stabilize enough to prevent widespread future failure events.…”