6.2 Integrated Estuary Management
151
land-marine transition zones (i) the Weser estuary and (ii) the Wadden Sea with the unique
Jade Bay (see Fig. 6.12). Surrounded by the North Sea and the river Weser, especially in
the northern part, and with a coastline of 160 km the Wesermarsch is characterized by an
almost prevailing saline environment. Also the ground water body is strongly influenced
by salt water penetrating underneath the peninsula. (Fig. 5.40). As shown in Sect. 4.2.2
and Fig. 4.6 the transition zone between saline and fresh ground water is oscillating.
Two-thirds of the whole county area (822 km 2 ) are situated below mean high water
level, which requires coastal protection by dikes and a comprehensive drainage system
consisting of ditches, canals, tidal gates and pumping stations. Nearly 80 % of the Wesermarsch is characterized by agricultural use, besides tourism and harbor industry it is one
of the most important economic sectors in this region. Marsh and peat soils occur predominantly in the county, 90 % of the agricultural land is under grassland farming (meat and
milk production).
Problem Description
Over centuries water management in the region Wesermarsch was affected by alternating
flooding events and land reclamation, shaping the current coastline. Todays coastline has
been established by building dikes over the last centuries while flood protection by dwelling mounds became less necessary simultaneously (e.g., Kramer, 1992). Dikes function
as an artificial barrier between land and sea, which makes a natural water exchange impossible. Accordingly, the Wesermarsch region is drained during winter time to discharge
the surplus of rainwater and watered in the late summer months to water the fields and
cattle by ditches.
Water (drainage) boards are responsible for the maintenance of this water management system in the Wesermarsch. The drainage boards Stadland, Brake and Butjadingen
are three of them (Fig. 6.12). The area of the drainage board Stadland is drained by ditches
via the Strohauser canal and discharges the water directly into the river Weser. Pumping
stations in the area of the drainage board are necessary to drain low lying areas. In Butjadingen six tidal gates are used to drain the area. The water is discharged into the North
Sea, the Jade Bay and the river Weser (red circles in Fig. 6.12). Depending on the water
level in the river and in the North Sea, the water has to be pumped or can be drained by
gravitation. The watering of the agricultural land in both regions is performed by extracting
fresh water from the river Weser.
Over the last decades problems regarding the drainage capacity in winter time and the
quality of fresh water in late summer occurred – see, for example, Ahlhorn et al. (2010);
Umlauf et al. (2011) and Bormann et al. (2012). More often the drainage system was not
sufficiently able to store and discharge the increasing amount of rainwater. In summer time
the salt concentration in the Weser exceeds the threshold for watering
7 due to an upstream
7 The watering is mainly used to flush the ditches to prevent standing water bodies and, thus, harmful diseases, but is also used to feed the cattle. Therefore, salinity should not exceed a certain
concentration.
151
land-marine transition zones (i) the Weser estuary and (ii) the Wadden Sea with the unique
Jade Bay (see Fig. 6.12). Surrounded by the North Sea and the river Weser, especially in
the northern part, and with a coastline of 160 km the Wesermarsch is characterized by an
almost prevailing saline environment. Also the ground water body is strongly influenced
by salt water penetrating underneath the peninsula. (Fig. 5.40). As shown in Sect. 4.2.2
and Fig. 4.6 the transition zone between saline and fresh ground water is oscillating.
Two-thirds of the whole county area (822 km 2 ) are situated below mean high water
level, which requires coastal protection by dikes and a comprehensive drainage system
consisting of ditches, canals, tidal gates and pumping stations. Nearly 80 % of the Wesermarsch is characterized by agricultural use, besides tourism and harbor industry it is one
of the most important economic sectors in this region. Marsh and peat soils occur predominantly in the county, 90 % of the agricultural land is under grassland farming (meat and
milk production).
Problem Description
Over centuries water management in the region Wesermarsch was affected by alternating
flooding events and land reclamation, shaping the current coastline. Todays coastline has
been established by building dikes over the last centuries while flood protection by dwelling mounds became less necessary simultaneously (e.g., Kramer, 1992). Dikes function
as an artificial barrier between land and sea, which makes a natural water exchange impossible. Accordingly, the Wesermarsch region is drained during winter time to discharge
the surplus of rainwater and watered in the late summer months to water the fields and
cattle by ditches.
Water (drainage) boards are responsible for the maintenance of this water management system in the Wesermarsch. The drainage boards Stadland, Brake and Butjadingen
are three of them (Fig. 6.12). The area of the drainage board Stadland is drained by ditches
via the Strohauser canal and discharges the water directly into the river Weser. Pumping
stations in the area of the drainage board are necessary to drain low lying areas. In Butjadingen six tidal gates are used to drain the area. The water is discharged into the North
Sea, the Jade Bay and the river Weser (red circles in Fig. 6.12). Depending on the water
level in the river and in the North Sea, the water has to be pumped or can be drained by
gravitation. The watering of the agricultural land in both regions is performed by extracting
fresh water from the river Weser.
Over the last decades problems regarding the drainage capacity in winter time and the
quality of fresh water in late summer occurred – see, for example, Ahlhorn et al. (2010);
Umlauf et al. (2011) and Bormann et al. (2012). More often the drainage system was not
sufficiently able to store and discharge the increasing amount of rainwater. In summer time
the salt concentration in the Weser exceeds the threshold for watering
7 due to an upstream
7 The watering is mainly used to flush the ditches to prevent standing water bodies and, thus, harmful diseases, but is also used to feed the cattle. Therefore, salinity should not exceed a certain
concentration.