Saltwater Intrusion — Ghyben-Herzberg & Well Upconing

A coastal aquifer in cross-section: pump a well, drop the freshwater table, and watch the saltwater wedge rise beneath it — roughly 40× faster than the table falls.

Well: Click the land to place the well
Cross-section view — ocean on the left, aquifer inland to the right
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Freshwater table h (m amsl)
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Interface depth (Ghyben-Herzberg, m)
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Upconing height (m)
SAFE
Contamination risk
Ghyben-Herzberg relation: depth of the freshwater-saltwater interface below sea level ≈ 40 × height of the freshwater table above sea level (z = h · ρf/(ρs−ρf), since seawater is about 2.5% denser than freshwater). Pump the well hard enough and the interface upcones straight into the screen.
About Saltwater Intrusion

Ghyben-Herzberg relation: at the interface, a column of freshwater of height (h+z) and a column of denser seawater of height z exert equal pressure: ρfg(h+z) = ρsgz, so z = h·ρf/(ρs−ρf) ≈ 40h.

Upconing: beneath a pumping well the interface rises locally, above and beyond the regional Ghyben-Herzberg trend, following roughly zup = 40Q / (2πKd), where d is the vertical gap between the well screen and the ambient interface. Past a critical pumping rate the cone becomes unstable and salt water is drawn straight into the well.

Sea level rise: raising the ocean boundary reduces the effective freshwater head everywhere, pushing the wedge further inland even with no change in pumping — a real, worsening threat as climate change raises sea levels.

Real-world cases: Miami-Dade, Jakarta, Bangkok, coastal California and the Nile Delta are all documented cases of coastal aquifers contaminated by over-pumping and rising seas.

About the Saltwater Intrusion Simulator

Coastal aquifers hold a lens of freshwater floating on top of denser, saltier water that is hydraulically connected to the ocean. Because seawater is about 2.5% denser than freshwater, the two fluids reach a stable, sloping interface rather than mixing instantly — a relationship first quantified independently by W. Badon Ghyben (1888) and Alexander Herzberg (1901). Balancing the pressure of a freshwater column against an equally tall seawater column at the interface gives the Ghyben-Herzberg approximation: the interface sits about 40 times deeper below sea level than the water table sits above it.

That 40× multiplier is what makes coastal aquifers so fragile. A pumping well that drops the local water table by just half a metre can, in principle, pull the underlying saltwater interface up by roughly 20 metres. Very close to a well, the simplified regional Ghyben-Herzberg trend breaks down and a sharper, localized rise called upconing takes over: the interface bulges directly beneath the well screen, and past a critical pumping rate that bulge becomes unstable, breaking through into the well and contaminating it with brackish or saline water.

This simulator lets you place a well in a coastal cross-section, choose its distance from shore and its screen depth, and vary the pumping rate. Watch the freshwater table draw down, the regional saltwater wedge respond via Ghyben-Herzberg, and — if you pump too hard, too close, or too shallow — the local upconing cone reach up and trigger a contamination warning. A recharge slider shows how rainfall infiltration pushes the wedge back, and a sea-level-rise slider demonstrates how climate change alone worsens intrusion even without any change in pumping.

Frequently Asked Questions

What is the Ghyben-Herzberg relation?

z ≈ 40h: the freshwater-saltwater interface sits about 40 times deeper below sea level than the water table sits above it, because seawater is roughly 2.5% denser than freshwater. It comes directly from balancing hydrostatic pressure between the two fluid columns at the interface.

Why does pumping cause saltwater intrusion?

Pumping lowers the freshwater table near the well. Since the interface depth scales with about 40 times the table height, a small drop in the table pulls the interface up by a much larger amount, bringing saline water closer to the well screen.

What is well upconing?

Upconing is the sharp, localized rise of the interface directly beneath a pumping well, layered on top of the regional Ghyben-Herzberg trend. Beyond a critical pumping rate the cone becomes unstable and saline water breaks through into the well screen.

Does sea level rise make intrusion worse?

Yes — raising the ocean boundary condition lowers the effective freshwater head everywhere in the aquifer, pushing the saltwater wedge further inland and shallower even with no change in pumping, compounding the risk from over-extraction.

Which real cities are affected by saltwater intrusion?

Miami-Dade and other South Florida well fields, Jakarta, Bangkok, coastal California, and parts of the Nile Delta and Mediterranean coast are all documented, ongoing cases of coastal aquifers contaminated by a combination of over-pumping and rising sea levels.

About this simulation

This simulation visualises a coastal aquifer using the Ghyben-Herzberg relation, z ≈ 40h, which relates the depth of the freshwater-saltwater interface below sea level (z) to the height of the freshwater table above sea level (h). Pumping a well lowers h locally, which pulls the interface up by roughly 40 times as much — and directly beneath the well screen a further, sharper effect called upconing can pull saline water straight into the well.

🔬 What it shows

A coastal cross-section with the ocean on the left and a land aquifer to the right. The blue freshwater lens floats over a darker saltwater wedge; the interface between them follows the Ghyben-Herzberg relation, bulging upward locally when the well pumps hard enough to trigger upconing.

🎮 How to use

Click the land area to place the well, then press Activate pumping. Adjust Pumping Rate Q (0–2000 m³/d), Well Distance from Coast (10–340 m), Well Screen Depth (5–38 m below sea level), Recharge (0–1000 mm/yr) and Sea Level Rise (0–2 m) and watch the freshwater table, interface depth, upconing height and contamination risk readouts respond live.

💡 Did you know?

Because seawater is only about 2.5% denser than freshwater, the Ghyben-Herzberg ratio ρf/(ρs−ρf) works out to roughly 40 — meaning a one-metre drop in a coastal water table can, in principle, pull the saltwater interface up by 40 metres.

Frequently asked questions

What is the Ghyben-Herzberg relation?

The Ghyben-Herzberg relation states that the depth of the freshwater-saltwater interface below sea level is about 40 times the height of the freshwater table above sea level. It follows from balancing hydrostatic pressure between a freshwater column and a slightly denser seawater column meeting at the interface, first described independently by W. Badon Ghyben in 1888 and Alexander Herzberg in 1901.

Why does pumping a coastal well cause saltwater intrusion?

Pumping lowers the freshwater table near the well. Because interface depth scales with roughly 40 times the table height, even a small drop in the table pulls the underlying saltwater interface up by a much larger amount, bringing saline water closer to the well screen and risking contamination.

What is well upconing?

Upconing is a localized, exaggerated rise of the saltwater interface directly beneath a pumping well, on top of the broader regional Ghyben-Herzberg trend. Past a critical pumping rate the upconed cone becomes unstable and saline water is drawn straight up into the well screen.

Does sea level rise make intrusion worse?

Yes. Raising the ocean boundary condition reduces the effective freshwater head throughout the aquifer, pushing the saltwater wedge further inland and shallower even without any increase in pumping — a real, compounding effect of climate change on coastal water supplies.

Which real cities suffer from saltwater intrusion?

Miami-Dade and other South Florida well fields, Jakarta, Bangkok, coastal California and parts of the Nile Delta and Mediterranean coast are all documented, ongoing cases where over-pumping and rising seas have pushed saline water into drinking-water aquifers.

How is saltwater intrusion managed in practice?

Water utilities reduce pumping rates near the coast, relocate wells further inland, inject treated freshwater to build a hydraulic barrier against the wedge, and continuously monitor water levels and salinity to keep the interface a safe distance below well screens.