Water retention area without agricultural land use at the primary sea wall (Research project 'COMTESS')
In the 19th and 20th century land was reclaimed from the sea to make use of the exposed fertile soils for agriculture through a process known as ‘impoldering’. The reclaimed land is now characterized by intensive grazing and cropland. This is a region where agriculture is the most important form of land use. However, the land needs to be regularly drained. Given the expected increase in precipitation in winter due to climate change, the corresponding increase in freshwater discharge needs to be managed. Furthermore, the periods when natural discharge into the sea oc-curs are likely to decrease – because of rising sea levels also caused by climate change. Consequently, in winter and spring, greater quantities of freshwater will need to be pumped into the sea rather than discharged naturally at the low or ‘ebb’ tide. Specially embanked water retention polders will be required to temporarily impound water as part of a multifunctional approach to coastal zone management.
Purpose of the Technology: These retention polders could be a cost-effective alternative to expensive invest-ments in extra pumping capacities to prevent submergence of low-lying cultivated areas. The primary aim is to restrict floods to the retention polders when the drain-age network is overburdened and cannot deal with the predicted extra demands in the future. The high evapotranspiration from the open waterbody, and the reeds growing within, will also help with reducing the amount of water. During dry sum-mers, the water in the retention polder could also be put to creative use as a source of irrigation. Another potential advantage is that subsurface saltwater intrusion in the region could be prevented by the freshwater-filled polders. During extreme storm surges and in the rare case of breaches in the sea wall, the retention polders would serve as an extra line of defence by holding seawater.
Establishment / maintenance activities and inputs: An embankment enclosing approx. 3,000 ha will be able to store up to 25,000,000 m³ water. This will improve the drainage of an area of approx. 49,000 ha. The invest-ment for building this water retention area is high – but for the reasons stated it serves a necessary purpose at a cost which is lower than the alternative – increased pumped drainage installations. Maintenance costs will be lower than the drainage alternative as only the integrity of the embankment needs to be monitored regularly. However within the proposed retention polders – the areas enclosed by the em-bankment - no agricultural activity will take place. This will lead to a change from the current intensive grazing for dairy farming and cropland to non-agricultural use. And therefore a development towards swamps, reed stands and open waters will take place. It is expected that a development to undisturbed natural habitats will increase the number of endangered species. There will be an accumulation of or-ganic material (and organic carbon) in the form of peat due to the wet conditions within the retention polders. Carbon will be sequestered by plant growth and thus reduce the amount of CO2 in the atmosphere. The natural regeneration within the embanked areas will be attractive for tourism and recreation, which should provide an opportunity for additional income generation for the local population.
Lieu: Landkreis Aurich, Germany, Lower Saxony, Allemagne
Nbr de sites de la Technologie analysés:
Diffusion de la Technologie: répartie uniformément sur une zone (33.7 km²)
Dans des zones protégées en permanence ?:
Date de mise en oeuvre: il y a entre 10-50 ans
Type d'introduction
| Spécifiez les intrants | Unité | Quantité | Coûts par unité (Euro) | Coût total par intrant (Euro) | % des coût supporté par les exploitants des terres |
| Main d'œuvre | |||||
| Labour | Dam | 1,0 | 21000000,0 | 21000000,0 | |
| Equipements | |||||
| Machine use | Dam | 1,0 | 9000000,0 | 9000000,0 | |
| Matériaux de construction | |||||
| Earth | Dam | 1,0 | 750000,0 | 750000,0 | |
| Coût total de mise en place de la Technologie | 30'750'000.0 | ||||
| Coût total de mise en place de la Technologie en dollars américains (USD) | 32'712'765.96 | ||||
| Spécifiez les intrants | Unité | Quantité | Coûts par unité (Euro) | Coût total par intrant (Euro) | % des coût supporté par les exploitants des terres |
| Main d'œuvre | |||||
| Labour | Dam | 1,0 | 800,0 | 800,0 | |
| Equipements | |||||
| Machine use | Dam | 1,0 | 300,0 | 300,0 | |
| Matériaux de construction | |||||
| Earth | Dam | 1,0 | 100,0 | 100,0 | 1,0 |
| Autre | |||||
| Maintenance per km ditch | Dam | 1,0 | 2270,7 | 2270,7 | |
| Coût total d'entretien de la Technologie | 3'470.7 | ||||
| Coût total d'entretien de la Technologie en dollars américains (USD) | 3'692.23 | ||||
No agricultural land use in the retention area any more.
No agricultural land use in the retention area any more.
Diversification of landscape by building the retention area will increase the attractivity for recreation and tourists.
No agricultural land use under wet conditions results in more diversity and conservation of regional species and habitats.
Updwelling of saline groundwater is prevented by increased water level in the retention area.
By water in the retention are the recharge of groundwater will increase and prevents salinization.
Instead of pumping water into the sea a higher amount is evapotranspirated naturally.
Typical for the region are wet situations. These typical wet conditions are restored by cessation of drainage system within the retention area.
By water in the retention are the recharge of groundwater will increase and prevent salinization.
By wetter conditions and due to cessation of land use, the soil organic matter will be increased and peat layers will established..
By wet conditions without land use the number of typical local species will be increased.
By wet conditions without land use the number of typical local species will be increased.
By wet conditions without land use the number of typical local habitats will be increased.
Modelled is the global warming potential by gas emissions. Not yet clear if it is benefit or disadvantage. Model will show.
Water stored in retention area can be used for irrigation during dry summer months.
Measured m3 of excess water in the catchment area, leading to floods or needs to be pumped. Exact values from modelling will be added as soon as possible!
Quantité avant la GDT: 49.000
Quantité après la GDT: 48.400
For the whole catchment area a loss of approx. 600 ha (size of retention area).
