The Mississippi Embayment aquifer is one of the largest alluvial groundwater aquifers in the United States. It is being excessively used, located along the lower Mississippi River covering approximately 202,019 km2(78,000 square miles). Annual average groundwater depletion in the aquifer has been estimated at 5.18 billion cubic meters (Gm3) (4.2 million acre‐feet) in 1981–2000. However, since 2000, annual groundwater depletion has increased abruptly to 8 Gm3(2001–2008). In recent years, multi‐state efforts have been initiated to improve the Mississippi Embayment aquifer sustainability. One management strategy of interest for preserving groundwater resources is managed aquifer recharge (MAR). In this study, we evaluate the impact of different MAR scenarios on land and water use decisions and the overall groundwater system using an economic model able to assess profitability of crop and land use decisions coupled to the Mississippi Embayment Regional Aquifer Study (MERAS) hydrogeologic model. We run the coupled model for 60 years by considering the hydrologic conditions from the MERAS model for the years 2002–2007 and repeating them 10 times. We find MAR is not economically attractive when the water cost is greater than $0.05/m3. Groundwater storage is unlikely to improve when relying solely on MAR as groundwater management strategy but rather should be implemented jointly with other groundwater conservation policies.
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.
more » « less- NSF-PAR ID:
- 10453866
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Water Resources Research
- Volume:
- 55
- Issue:
- 4
- ISSN:
- 0043-1397
- Page Range / eLocation ID:
- p. 2742-2759
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract In water‐stressed regions of the world, the inundation of working landscapes to replenish aquifers—known as flood‐managed aquifer recharge (flood‐MAR)—has become a valuable tool for sustainable groundwater management. Due to their diverse land use histories, however, many potential recharge sites host nonpoint source contaminants (such as salts, pesticides, and fertilizers) within the vadose zone that may flush to groundwater during recharge operations. To identify the controls on contaminant migration, we perform stochastic simulations of flood‐MAR through a heterogeneous alluvial aquifer and apply transient particle tracking to evaluate conservative and reactive contaminant transport over 80 years of recharge operations. With semi‐annual recharge events, the water table begins to rise 0.13–1.84 years after the first inundation event while solutes take much longer (11 to 80 years) to transit the 45‐m thick unsaturated zone. We derive a parametric expression for the ratio of celerity (or rate of pressure transmission) to velocity of the flood‐MAR wetting front and show that this simplified expression agrees with values calculated from heterogeneous model simulations. Slow solute velocities (0.25–1.75 m year−1) allow for significant contaminant removal through denitrification, but the contaminant plume experiences minimal dispersion or dilution over this time, reaching the water table as a sharp front. Our results suggest that minimizing groundwater velocity and maximizing groundwater celerity during flood‐MAR should optimize increases in water supply while limiting water quality degradation.
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Abstract Groundwater resources are vital to ecosystems and livelihoods. Excessive groundwater withdrawals can cause groundwater levels to decline1–10, resulting in seawater intrusion11, land subsidence12,13, streamflow depletion14–16and wells running dry17. However, the global pace and prevalence of local groundwater declines are poorly constrained, because in situ groundwater levels have not been synthesized at the global scale. Here we analyse in situ groundwater-level trends for 170,000 monitoring wells and 1,693 aquifer systems in countries that encompass approximately 75% of global groundwater withdrawals18. We show that rapid groundwater-level declines (>0.5 m year−1) are widespread in the twenty-first century, especially in dry regions with extensive croplands. Critically, we also show that groundwater-level declines have accelerated over the past four decades in 30% of the world’s regional aquifers. This widespread acceleration in groundwater-level deepening highlights an urgent need for more effective measures to address groundwater depletion. Our analysis also reveals specific cases in which depletion trends have reversed following policy changes, managed aquifer recharge and surface-water diversions, demonstrating the potential for depleted aquifer systems to recover.
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null (Ed.)Climate change, drought, and chronic overdraft represent growing threats to the sustainability of water supplies in dry environments. The Monterey/Salinas region in California exemplifies a new era of integrated or “one water” management that is using all of the water it can get to achieve more sustainable supplies to benefit cities, agriculture, and the environment. This program is the first of its kind to reuse a variety of waters including wastewater, stormwater, food industry processing water, and agricultural drainage water. This study investigates the partnerships, projects, and innovations that shape Monterey’s integrated water network in order to better understand the challenges and opportunities facing California communities as they seek to sustainably manage peri-urban water supplies. Water reuse in the Monterey region produces substantial economic and environmental benefits, from tourism and irrigation of high-value crops to protection of groundwater and increases in environmental flows and water quality. Water resource managers in other communities can learn from Monterey’s success leveraging local needs and regional partnerships to develop effective integrated water solutions. However, key challenges remain in resolving mismatched timing between water availability and demand, funding alternative water supplies, and planning effectively under uncertainty. Opportunities exist to increase Monterey’s recycled water supply by up to 50%, but this requires investment in seasonal storage and depends on whether desalination or additional recycling forms the next chapter in the region’s water supply story. Regulatory guidance is needed on seasonal subsurface storage of tertiary-treated recycled water as distinct from potable recharge. By increasing the supply of recycled water to Monterey’s indirect potable use system, the region’s potential need for seawater desalination may be delayed as much as 30 years, resulting in cost and energy savings, and giving the opportunity to resolve present planning concerns.more » « less
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Abstract Managed aquifer recharge (MAR) can provide long‐term storage of excess surface water for later use. While decades of research have focused on the physical processes of MAR and identifying suitable MAR locations, very little research has been done on how to consider competing factors and tradeoffs in siting MAR facilities. This study proposes the use of a simulation‐optimization (SO) framework to map out a cost‐effectiveness frontier for MAR by combining an evolutionary algorithm with two objective functions that seek to maximize groundwater storage gains while minimizing MAR cost. We present the theoretical framework along with a real‐world application to California's Central Valley. The result of the SO framework is a Pareto front that allows identifying suitable MAR locations for different levels of groundwater storage gain and associated MAR project costs, so stakeholders can evaluate different choices based on cost, benefits, and tradeoffs of MAR sites. Application of the SO framework to the Central Valley shows groundwater can be recharged from high‐magnitude (95th percentile) flows at a marginal cost of $57 to $110 million per km3. If the 10 percent largest flows are recharged the total groundwater storage gain would double and the marginal costs would drop to between $30 and $50 million per km3. If recharge water is sourced from outside local basins (e.g., the Sacramento‐San Joaquin Delta), groundwater storage gain is approximately 25%–80% greater than can be achieved by recharging local flows, but the total cost is about 10%–15% higher because of additional lift cost.
