Saltwater intrusion occurs when saline water from the ocean moves into freshwater aquifers located near the coast. It is often caused by groundwater pumping or construction activities that provide pathways for saltwater. Saltwater intrusion impacts freshwater resources and can lead to the loss of vegetation. The Ghyben-Herzberg relation describes the interaction between fresh and saltwater, and estimates that for every foot of freshwater above sea level, there will be 40 feet below. Management strategies aim to maintain groundwater levels and include conservation, alternative water sources, recharge, and monitoring wells.

1. SEAWATER INTRUSION

2. INTRODUCTION
Almost two thirds of the world's population lives within 400
km of the ocean shoreline; just over half live within 200 km,
an area only taking up 10% of the earth's surface (Hinrichsen,
2007).
Most of these coastal regions rely on groundwater as their
main source of fresh water for domestic, industrial and
agricultural purposes.
As the world's population continues to grow at an alarming
rate, fresh water supplies are constantly being depleted,
bringing with it issues such as saltwater intrusion and
increasing the importance of groundwater monitoring,
management, and conservation.

3. Saltwater intrusion
Saltwater intrusion is a major concern commonly
found in coastal aquifers around the world.
Saltwater intrusion is the movement of saline water
into freshwater aquifers.
Most often, it is caused by ground-water pumping
from coastal wells, or from construction of navigation
channels or oil field canals.

4. The channels and canals provide conduits
for salt water to be brought into fresh
water marshes. Salt water intrusion can
also occur as the result of a natural
process like a storm surge from a
hurricane.
Saltwater intrusion occurs in virtually
all coastal aquifers, where they are in
hydraulic continuity with seawater.

6. Cause and Impact of
Saltwater Intrusion

7. • Saltwater intrusion happens when saltwater is drawn
in (from the sea) into fresh water aquifers .
• Sea water has a higher density (which is because it
carries more solutes) than freshwater.
causes

8. • This density causes the pressure under a column of
salt water to be greater than the pressure under a
column of the same height of freshwater.
• If these two columns are connected at the bottom,
then the pressure difference would cause a flow of
saltwater column to the freshwater until the
pressure equalizes
• To prevent this more and more countries adopt
Extensive monitoring schemes and numerical models
to assess how water can be pumped without problems

9. Saltwater intrusion into freshwater aquifers is also
influenced by factors such as:
 tidal fluctuations,
long-term climate and sea level changes,
fractures in coastal rock formations
seasonal changes in evaporation and recharge rates.

10. Recharge rates can also be lowered in areas with
increased urbanization and thus impervious surfaces.
 Intrusion has also occurred in areas because of
water levels being lowered by the construction of
drainage canals (Barlow, 2003).

13. IMPACTS
• Salt-water intrusion from rising sea levels
will reduce the quality and quantity of
freshwater supplies as it is happening along
Atlantic and Gulf coasts.
• This is a major concern, since billions of people
already lack access to freshwater.
• Salt water intrusion leads to the loss of fresh water
vegetation
• Spread of mudflats into previously vegetative areas.

14. GHYBEN-HERZBERG RELATION
The first physical formulations of saltwater intrusion were
made by W. Badon-Ghijben(1888,1889) and A.Herzberg
(1901), thus called the Ghyben-Herzberg relation.
They derived analytical solutions to approximate the
intrusion behavior , which are based on a number of
assumptions that do not hold in all field cases.

15. The figure shows the Ghyben-Herzberg relation. In the equation,
This figure shows the Ghyben-Herzgerg Relation. In the equation,
Where,h=thickness of the fresh water zone above sea level
z=thickness of the freshwater zone below sea level

18. The Ghysen-Herzberg 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.
This analysis assumes hydrostatic conditions in a
homogeneous, unconfined coastal aquifer. According
to this relation, if the water table in an unconfined
coastal aquifer is lowered by 1m, the salt-water
interface will rise 40 m.

19. CONTROL AND
MANAGEMENT OF
SEAWATER INTRUSION

20. • To maintain the proper balance between water
being pumped from an aquifer and the amount of
water recharging it.
• Constant monitoring of the salt-water interface is
necessary in determining the proper management
technique. .
• Efforts towards the promotion of water
conservation, and restricting withdrawals from
coastal aquifers have been the focus in many
areas.

21. • Using alternative freshwater sources has also been
encouraged. Ocean water desalination plants are
showing up in coastal regions around the world.
• Where there are no other options for fresh water, efforts
to maintain groundwater levels by ponding surface water
and storm water runoff, or using river water to recharge
the groundwater table have been successfully
implemented.
• Aquifer Storage and Recovery (ASR) systems can help
restore aquifers that have experienced long-term declines
in water levels due to over-pumping.

22. Other methods to control saltwater intrusion, such as
using deep recharge wells, have also been successful.
These wells create a high Potentiometric surface,
which allows for the pumping of groundwater below
sea level landward of a groundwater ridge created.
In some instances, barrier wells have been set up near
the shore to pump out salt water and recharge a fresh
water gradient toward the sea.

23. Physical separation by barriers – construction of
artificial subsurface barriers.
Recharge pits – artificial recharge in areas of
production wells
Injection wells – to create pressure ridge( barrier) to
prevent intrusion

24. Deep recharge well

26. Monitoring well networks allow continuous observation of
the saltwater interface, after management strategies have been
put in place.
This provides early warnings of saltwater intrusion and tracks
the effectiveness of the strategy. Overall, proper groundwater
monitoring techniques and groundwater management,
combined with groundwater conservation are needed to keep
saltwater intrusion under control, and ensure fresh water
supplies are sustained for future generations.