Coastal Brine Pumping Reshapes Seawater Intrusion in China’s Weibei Plain

Along the southern shore of Laizhou Bay in Shandong Province, China, two very different pumping operations are quietly reshaping the underground boundary between fresh water and the sea. Inland, farmers and cities draw fresh groundwater from aquifers that have sustained agriculture for decades. Near the coast, industry extracts ancient saline brine, a resource rich in salts used for chemical production. A new modeling study of the Weibei Plain shows that these two activities, acting together, have carved out a striking pattern of depressions in the water table that is accelerating seawater intrusion, and it identifies a counterintuitive management strategy that could slow the damage.

The research, published in Environmental Monitoring and Assessment by Qinghe Fan, Chao Jia, Xiao Yang and Yan Li, is based on a three-dimensional variable-density groundwater flow and solute transport model covering the phreatic and confined aquifer systems within 150 meters of the surface. Unlike simpler models that treat groundwater as a single fluid of uniform density, variable-density models capture the physics that matters most in coastal settings: saline water is denser than fresh water, so the two do not simply mix but form a wedge-shaped interface whose position shifts as pumping changes hydraulic gradients. Getting this density coupling right is essential when the question is precisely where the salt front will move next.

The team built their model on regional hydrogeological conditions and long-term monitoring data, calibrating it against observed chloride distributions and hydraulic heads before using it to explore the future. Four pumping scenarios were designed to test how different patterns of groundwater extraction influence the dynamics of seawater intrusion. This scenario-based approach is a standard but powerful tool in coastal hydrogeology: rather than attempting to predict a single future, the model reveals how the system responds to alternative management choices, giving water managers a quantitative basis for decisions that would otherwise rest on intuition.

The simulations revealed a phenomenon the authors describe as a dual-cone depression system. Decades of long-term, spatially unbalanced extraction have lowered the water table in two distinct zones. In the landward freshwater zone, heavy pumping of fresh water has created one cone of depression. In the seaward coastal saline zone, brine extraction has created a second. Between these two depressions, a groundwater divide has formed, a ridge of relatively higher hydraulic head that separates the two drawdown areas. This divide fundamentally alters the regional flow regime, redirecting groundwater gradients in ways that increase the potential for seawater to migrate inland through the aquifer.

The simulated chloride distributions show that the intrusion boundary has not advanced uniformly along the coast. In some sectors the salt front has moved landward, while in others it has actually shifted seaward, a heterogeneity that reflects the interplay between the two pumping centers and the geometry of the aquifer system. Despite this patchiness, the total area affected by intrusion has increased overall. This finding matters for monitoring programs: a single transect of observation wells might report stable or even improving conditions while the intrusion front expands elsewhere, so spatially comprehensive monitoring is essential for tracking the true state of the aquifer.

Perhaps the most consequential result is the identification of the primary driver. Freshwater overextraction in the landward freshwater zone, not brine pumping at the coast, emerged as the dominant cause of intrusion expansion. This runs against a common assumption that coastal saline-water extraction is the main threat to aquifer salinity. In the Weibei Plain, the inland drawdown steepens the hydraulic gradient toward the interior, pulling seaward water landward across the interface. Brine extraction in the seaward zone plays a different role: it modifies the local hydraulic gradient and influences the position of the groundwater divide, which means it can either aggravate or partially counteract the inland pumping effect depending on how it is managed.

That insight opens the door to the study’s most striking recommendation. When the team tested management scenarios, combined strategies outperformed any single measure. The best-performing scheme paired a 30 percent reduction in freshwater extraction in the landward zone with a controlled 30 percent increase in brine extraction in the seaward coastal saline zone. Increasing brine pumping sounds like the opposite of what a coastal aquifer needs, but the simulation showed it produced the smallest increase in both the spatial extent of seawater intrusion and chloride concentrations among all tested scenarios. By strategically deepening the seaward depression, the coordinated scheme holds the groundwater divide in a position that limits the landward pull on the salt front, while the freshwater cutback relieves the inland stress that drives intrusion in the first place.

The implications extend well beyond Shandong Province. Coastal aquifers supply drinking water and irrigation to a large share of the world’s population, and seawater intrusion is a growing threat wherever extraction outpaces recharge, a problem compounded by sea-level rise and reduced recharge under changing climate conditions. The Weibei Plain adds a distinctive twist because it hosts economically valuable brine resources, so simply shutting down coastal extraction is not an option for local industry. The study demonstrates that integrated regulation of freshwater and brine extraction together offers a feasible pathway to mitigate intrusion while still allowing brine resource utilization, a balance that single-sector management cannot achieve.

For groundwater managers, the practical lessons are concrete. First, intrusion control should target the dominant driver, which in this system means prioritizing reductions in landward freshwater pumping, through efficiency measures, alternative supplies, or allocation limits. Second, coastal brine extraction should not be viewed purely as a liability; when regulated deliberately, it can be tuned to reinforce rather than undermine the hydraulic conditions that keep salt at bay. Third, scenario modeling of this kind, grounded in monitoring data and validated against observed chloride distributions, provides a defensible quantitative framework for setting extraction quotas. The authors note that their findings offer scientific support for sustainable groundwater management in coastal areas where brine extraction is part of the economic fabric, and the coordinated 30-30 scheme gives regulators a starting point that can be refined as monitoring data accumulate.

The study also underscores how much depends on understanding the three-dimensional architecture of coastal aquifer systems. Shallow phreatic aquifers and deeper confined layers respond differently to pumping, and the vertical exchange between them controls how quickly saline water can spread downward or upward. By modeling both systems within the top 150 meters of the Weibei Plain, the researchers captured interactions that two-dimensional or single-layer models would miss. As coastal regions worldwide face intensifying competition between freshwater demand and saline resource development, this work suggests that the future of coastal groundwater management lies not in choosing between uses, but in engineering their combined hydraulics with the same care that engineers apply to surface reservoirs.

Subject of Research: Numerical simulation of seawater intrusion under combined freshwater and brine extraction in the coastal aquifers of the Weibei Plain, China

Article Title: Numerical simulation and assessment of seawater intrusion under coastal brine extraction: implications for groundwater management in the Weibei Plain, China

Article References: Fan, Q., Jia, C., Yang, X., & Li, Y. (2026). Numerical simulation and assessment of seawater intrusion under coastal brine extraction: implications for groundwater management in the Weibei Plain, China. Environmental Monitoring and Assessment, 198(10), Article 1055. https://doi.org/10.1007/s10661-026-15903-z

Image Credits: AI Generated

DOI: 10.1007/s10661-026-15903-z

Keywords: seawater intrusion, coastal aquifers, groundwater management, brine extraction, variable-density flow, numerical simulation, Weibei Plain, Laizhou Bay, chloride transport, groundwater divide, Shandong, sustainable water resources