4.2 Impacts of the Sea on Coastal Fresh Water Systems
57
River discharge Q
C
salt [%]
ΔC
salt [‰]
Transition zone
High tide
Low tide
Q high
Q low
Q high
Q low
Q low
Q high
Ocean
River
Fig. 4.9 Movement of the brackish water zone in estuaries: During high tides, the brackish zone
moves upstream compared to low tide. By contrast, large river flows lead to a downstream movement
of the brackish zone in the estuary. C salt : salt concentration; C salt : change in salt concentration;
Q high : high river discharge; Q low : low river discharge. Source: changed after Baumgartner and
Liebscher (1996)
Ground Water
Coastal and island aquifers are prone to sea water intrusion. Because saline water is denser
than fresh water, it invades aquifers which are hydraulically connected to the ocean. Like
in the surface water bodies, the transition zone is a zone of mixing between fresh and salt
water. Under equilibrium conditions, the interface remains fixed. The transition zone is
found in the ground water along the coastline. Since flow processes usually are slow in
the ground water, the transition zone is relatively narrow (Fig. 4.10). Intense fresh water
drainage or fresh water abstraction on the land side can induce further expansion of the
saline ground water landwards.
Islands develop their own fresh water lenses. Under natural conditions, fresh water
forms a lens that floats on the top of a base of salt water. Recharge is happening due to
infiltration of rainwater into the fresh water lens (Fig. 4.11).
Sea water intrusion must be addressed in managing ground water resources in island and coastal areas. The fresh water lens is very susceptible to contamination,
57
River discharge Q
C
salt [%]
ΔC
salt [‰]
Transition zone
High tide
Low tide
Q high
Q low
Q high
Q low
Q low
Q high
Ocean
River
Fig. 4.9 Movement of the brackish water zone in estuaries: During high tides, the brackish zone
moves upstream compared to low tide. By contrast, large river flows lead to a downstream movement
of the brackish zone in the estuary. C salt : salt concentration; C salt : change in salt concentration;
Q high : high river discharge; Q low : low river discharge. Source: changed after Baumgartner and
Liebscher (1996)
Ground Water
Coastal and island aquifers are prone to sea water intrusion. Because saline water is denser
than fresh water, it invades aquifers which are hydraulically connected to the ocean. Like
in the surface water bodies, the transition zone is a zone of mixing between fresh and salt
water. Under equilibrium conditions, the interface remains fixed. The transition zone is
found in the ground water along the coastline. Since flow processes usually are slow in
the ground water, the transition zone is relatively narrow (Fig. 4.10). Intense fresh water
drainage or fresh water abstraction on the land side can induce further expansion of the
saline ground water landwards.
Islands develop their own fresh water lenses. Under natural conditions, fresh water
forms a lens that floats on the top of a base of salt water. Recharge is happening due to
infiltration of rainwater into the fresh water lens (Fig. 4.11).
Sea water intrusion must be addressed in managing ground water resources in island and coastal areas. The fresh water lens is very susceptible to contamination,