The Ghyben-Herzberg Relation (Saltwater Intrusion) calculator computes the depth of fresh water in an aquifer below sea level (z) based on the depth of fresh water above sea level (h).
INSTRUCTIONS: Choose units and enter the following:
- (h) Depth or thickness of Freshwater zone above sea level
- (ρf) Density of Freshwater (1.000 g/cm3)
- (ρs) Density of Saltwater (1.025 g/cm3)
Depth of Fresh Water below Sea Level (z): The calculator returns the depth (z) in feet. However, this can be automatically converted to other length units via the pull-down menu.
The Science
The Ghyben-Herzberg Relation (Saltwater Intrusion) ratio states that for every foot of fresh water in an unconfined aquifer above sea level, there will be forty feet of fresh water in the aquifer below sea level. The formula for the depth of fresh water below sea level is: 
z=ρf /(ρs - ρf) • h
where:
- z = depth of fresh water below sea level
- h = thickness of the freshwater zone above sea level
- ρf = density of freshwater (1.000 g/cm3)
- ρs = density of saltwater (1.025 g/cm3)
Saltwater Intrusion is the movement of saline water in freshwater aquifers, which can lead to contamination of drinking sources and other consequences. Saltwater intrusion occurs naturally to some degree in most coastal aquifers, owing to they hydraulic connection between groundwater and seawater. Because saltwater has a higher mineral content than freshwater, it is denser and a higher water pressure. As a result, saltwater can push inland beneath freshwater. Certain human activities, especially groundwater pumping from coastal freshwater wells, have increased saltwater intrusion in many coastal areas. Water extraction drops the level of fresh groundwater, reducing its water pressure and allowing saltwater to flow further inland. Other contributors to saltwater intrusion include navigation channels or agricultural and drainage channels, which provide conduits for saltwater to move inland, and sea level rise. Saltwater intrusion can also be worsened by extreme events like hurricane storm surges.
Water Related Calculators
- Underwater Pressure
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- Density of water at STP
- Density of seawater
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- Water Density by Temperature
- Compute the Depth of Water associated with a Pressure
- Bernoulli's Equation (Pressure)
- Bernoulli's Equation (Velocity)
- Bernoulli's Equation (Elevation)
- Volume of Water in a Well
References
Wikipedia (https://en.wikipedia.org/wiki/Saltwater_intrusion#Ghyben-Herzberg_relation)