Hydrology of (Shallow) Coastal Regions
Helge Bormann
4
4.1 The Water Cycle of Coastal Areas
The water cycle of coastal regions is characterized by the interplay between the different
hydrological processes. It can be described by the general water balance equation of a
system, quantifying the change of water in a defined area:
S = P – ET + Q in – Q out
(4.1)
where S = change in water storage, P = precipitation, ET = evapotranspiration, Q in =
inflow, Q out = outflow.
Looking at a catchment, defined by the absence of lateral inflow across the catchment
boundaries, Eq. 4.1 reduces to
P = ET + Q + S
(4.2)
where Q = runoff. This means that precipitation splits up in evapotranspiration and runoff,
and can replenish or reduce the catchment storage.
Due to the humid climate, many coastal regions have a positive water balance, for
example, the North Sea Region in central Europe. In case of a positive water balance,
the precipitation P exceeds the evapotranspiration ET. The excess water either generates
runoff or is temporally stored in the hydrological system (Fig. 4.1).
In the neighborhood of estuaries, which are defined as partially enclosed coastal body
of brackish water with one or more rivers flowing into it, and with a free connection to
the open sea, and tidal rivers, coastal regions are also influenced by rivers conveying the
excess water of inland catchments to the sea. High flows, inducing high water levels, can
lead to inundations while low flows accelerate the drainage of the respective area.
c
Springer Fachmedien Wiesbaden GmbH 2018
49
F. Ahlhorn, Integrated Coastal Zone Management,
Wasser: Ökologie und Bewirtschaftung, DOI 10.1007/978-3-658-17052-3_4
Helge Bormann
4
4.1 The Water Cycle of Coastal Areas
The water cycle of coastal regions is characterized by the interplay between the different
hydrological processes. It can be described by the general water balance equation of a
system, quantifying the change of water in a defined area:
S = P – ET + Q in – Q out
(4.1)
where S = change in water storage, P = precipitation, ET = evapotranspiration, Q in =
inflow, Q out = outflow.
Looking at a catchment, defined by the absence of lateral inflow across the catchment
boundaries, Eq. 4.1 reduces to
P = ET + Q + S
(4.2)
where Q = runoff. This means that precipitation splits up in evapotranspiration and runoff,
and can replenish or reduce the catchment storage.
Due to the humid climate, many coastal regions have a positive water balance, for
example, the North Sea Region in central Europe. In case of a positive water balance,
the precipitation P exceeds the evapotranspiration ET. The excess water either generates
runoff or is temporally stored in the hydrological system (Fig. 4.1).
In the neighborhood of estuaries, which are defined as partially enclosed coastal body
of brackish water with one or more rivers flowing into it, and with a free connection to
the open sea, and tidal rivers, coastal regions are also influenced by rivers conveying the
excess water of inland catchments to the sea. High flows, inducing high water levels, can
lead to inundations while low flows accelerate the drainage of the respective area.
c
Springer Fachmedien Wiesbaden GmbH 2018
49
F. Ahlhorn, Integrated Coastal Zone Management,
Wasser: Ökologie und Bewirtschaftung, DOI 10.1007/978-3-658-17052-3_4