1.2 Coordonnées des personnes-ressources et des institutions impliquées dans l'évaluation et la documentation de la Technologie

Nom du projet qui a facilité la documentation/ l'évaluation de la Technologie (si pertinent)

Book project: Making sense of research for sustainable land management (GLUES)

Nom du projet qui a facilité la documentation/ l'évaluation de la Technologie (si pertinent)

Sustainable Coastal Land Management (COMTESS / GLUES)

Nom du ou des institutions qui ont facilité la documentation/ l'évaluation de la Technologie (si pertinent)

University of Oldenburg (University of Oldenburg) - Allemagne

1.3 Conditions relatives à l'utilisation par WOCAT des données documentées

Quand les données ont-elles été compilées (sur le terrain)?

09/06/2015

Le compilateur et la(les) personne(s) ressource(s) acceptent les conditions relatives à l'utilisation par WOCAT des données documentées:

Oui

1.5 Référence au(x) questionnaire(s) sur les Approches de GDT

2.1 Courte description de la Technologie

Définition de la Technologie:

Water retention polders to reduce flood risk due to heavy rainfall or runoff at high tide in coastal lowlands. The retention polders are used to accumulate organic material for climate change mitigation and enable development of undisturbed natural habitats, rather than for agriculture.

2.2 Description détaillée de la Technologie

Description:

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.

2.3 Photos de la Technologie

2.5 Pays/ région/ lieux où la Technologie a été appliquée et qui sont couverts par cette évaluation

2.6 Date de mise en œuvre de la Technologie

Si l'année précise est inconnue, indiquez la date approximative: :

• il y a entre 10-50 ans

2.7 Introduction de la Technologie

Spécifiez comment la Technologie a été introduite: :

• au cours d'expérimentations / de recherches
• par le biais de projets/ d'interventions extérieures

3.2 Type(s) actuel(s) d'utilisation des terres, là où la Technologie est appliquée

Commentaires:

Major land use problems (compiler’s opinion): Flood events and droughts may substantially disrupt the current land use system in the future and lead to higher drainage costs and higher economic risks for agricultural production. This will reduce the ecological and economic viability of the current intensive and highly productive land use under a changing climate.

Major land use problems (land users’ perception): There is no awareness of risks due to climate change.

Future (final) land use (after implementation of SLM Technology): Other: Oo: Other: wastelands, deserts, glaciers, swamps, recreation areas, etc

Constraints of infrastructure network (roads, railways, pipe lines, power lines): needs to be adapted to regular flooding

Constraints of recreation (landscape is used for reacreation and tourism): change in landscape due to retention area

Constraints of nature conservation areas (protected sites): wetter conditions in retention area

Si l'utilisation des terres a changé en raison de la mise en œuvre de la Technologie, indiquez l'utilisation des terres avant la mise en œuvre de la Technologie:

Mixed: Mp: Agro-pastoralism

3.3 Informations complémentaires sur l'utilisation des terres

Commentaires:

Water supply: rainfed, mixed rainfed - irrigated

Nombre de période de croissance par an: :

• 1

Précisez:

Longest growing period in days: 240 Longest growing period from month to month: March to October

Densité d'élevage/ chargement (si pertinent):

> 100 LU /km2

3.4 Groupe de GDT auquel appartient la Technologie

• gestion des eaux de surface (sources, rivières, lacs, mers)
• gestion/ protection des zones humides

• Flood prevention

3.5 Diffusion de la Technologie

Commentaires:

Total area covered by the SLM Technology is 33.7 m2.

3.6 Mesures de GDT constituant la Technologie

Commentaires:

Main measures: structural measures

Secondary measures: management measures

3.7 Principaux types de dégradation des terres traités par la Technologie

Commentaires:

Main type of degradation addressed: Hs: change in quantity of surface water

Secondary types of degradation addressed: Cs: salinisation / alkalinisation, Hg: change in groundwater / aquifer level, Hq: decline of groundwater quality

Main causes of degradation: change of seasonal rainfall (Climate change, higher rainfall in winter, lower in summer), Heavy / extreme rainfall (intensity/amounts) (Heavy rainfall in winter due to climate change expected), floods (Flooding due to heavy rainfall in winter)

Secondary causes of degradation: droughts (Droughts due to less rainfall in summer (climate change)), other natural causes (avalanches, volcanic eruptions, mud flows, highly susceptible natural resources, extreme topography, etc.) specify (Sea level rise)

3.8 Prévention, réduction de la dégradation ou réhabilitation des terres dégradées

Spécifiez l'objectif de la Technologie au regard de la dégradation des terres:

• prévenir la dégradation des terres
• réduire la dégradation des terres

Commentaires:

Main goals: prevention of land degradation

Secondary goals: mitigation / reduction of land degradation

4.1 Dessin technique de la Technologie

4.2 Spécification/ explications techniques du dessin technique

The figure shows the study region, located on the North Sea coast. The whole area is protected by a sea wall (grey). Crop fields (yellow), grasslands (green) and the drainage system (light blue) char-acterize the region. Large water bodies (blue) sur-rounded by reeds (brown) act as water retention polders. Vegetative regeneration, build-up of peat and re-establishment of natural habitats occurs within the retention polders. The land around the retention polders (the higher parts of the land-scape) profits from the retention areas as the risk of flooding is reduced and can be used for cropland and intensive grazing. Depending on the size of the retention area a huge amount of excess water can be contained. Retention areas of 3,000 ha are able to store up to 25,000,000 m³ water. The height of the dams depends on the elevation of the landscape but in general a height of less than 2 m is sufficient.

Location: Krummhörn. County of Aurich, Lower Saxony

Technical knowledge required for field staff / advisors: high (To generate income in the retention area (without existing agricultural methods))

Technical knowledge required for Water board: high (To build a new adapted drainage system with retention areas)

Main technical functions: control of dispersed runoff: retain / trap, control of concentrated runoff: retain / trap

Secondary technical functions: increase in organic matter, increase / maintain water stored in soil, increase of groundwater level / recharge of groundwater

Dam/ pan/ pond
Height of bunds/banks/others (m): 1
Width of bunds/banks/others (m): 2
Length of bunds/banks/others (m): 30000

Construction material (earth): sand core and clay cover

Specification of dams/ pans/ ponds: Capacity 25000000m3

Catchment area: 49000ham2

Beneficial area: 49000ham2

Other specifications: size of retention area (embanked area): 3,000.00 ha

Change of land use type: The former pastures and crop fields will not be used any more. Cessation of land use will take place.

Change of land use practices / intensity level: No more agricultural land use within the retention areas. The wetter conditions will lead to peat accumulation

4.3 Informations générales sur le calcul des intrants et des coûts

autre/ monnaie nationale (précisez):

Euro

Indiquer le taux de change du dollars en monnaie locale (si pertinent): 1 USD= :

0,94

4.4 Activités de mise en place/ d'établissement

	Activité	Type de mesures	Calendrier
1.	Building of dams	Structurel	during winter months

4.5 Coûts et intrants nécessaires à la mise en place

	Spécifiez les intrants	Unité	Quantité	Coûts par unité	Coût total par intrant	% 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					30750000,0

Commentaires:

Duration of establishment phase: 3 month(s)

4.6 Activités d'entretien/ récurrentes

	Activité	Type de mesures	Calendrier/ fréquence
1.	Control of dams	Structurel	once a year
2.	Maintenance of dams	Structurel	once a year
3.	Maintanance of drainage system	Structurel	once a year

4.7 Coûts et intrants nécessaires aux activités d'entretien/ récurrentes (par an)

	Spécifiez les intrants	Unité	Quantité	Coûts par unité	Coût total par intrant	% 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					3470,7

Commentaires:

Machinery/ tools: digger, open truck

The main investment is based on a dam length of 30 km to build up the retention area of a size of 3 000 ha. The length of the drainage network for the whole watershed is 1,074 km. Within the retention area no maintenance of the drainage network is necessary as there is no agricultural land use and drainage is not maintained any more. Maintenance costs of drainage network are based on long term annual mean cost of 2,270.72 Euro per km including pumping costs.

4.8 Facteurs les plus importants affectant les coûts

Décrivez les facteurs les plus importants affectant les coûts :

The establishment costs are for the whole retention area (3 000 ha). The establishment period will be half a year.
Mainly the elevation in the region determines the costs as the height of the dams depend on the elevation. Typical heights are 1 m up to 2 m with a slope of 1:3.

5.1 Climat

5.2 Topographie

5.3 Sols

Si disponible, joignez une description complète du sol ou précisez les informations disponibles, par ex., type de sol, pH/ acidité du sol, capacité d'échange cationique, azote, salinité, etc.

Soil fertiliuty is high
Soil drainage/infiltration is medium
Soil water storage capacity is high

5.4 Disponibilité et qualité de l'eau

5.5 Biodiversité

5.6 Caractéristiques des exploitants des terres appliquant la Technologie

Indiquez toute autre caractéristique pertinente des exploitants des terres:

Land users applying the Technology are mainly common / average land users

Population density: 50-100 persons/km2

Annual population growth: < 0.5%

1% of the land users are very rich and own 1% of the land.
50% of the land users are rich and own 24% of the land.
50% of the land users are average wealthy and own 50% of the land.
and own 25% of the land.

Off-farm income specification: Many farmers do additional work in industry or servicing sector

5.7 Superficie moyenne des terres détenues ou louées par les exploitants appliquant la Technologie

5.8 Propriété foncière, droits d’utilisation des terres et de l'eau

Propriété foncière:

• individu, sans titre de propriété

Droits d’utilisation des terres:

• individuel

5.9 Accès aux services et aux infrastructures

6.1 Impacts sur site que la Technologie a montrés

Impacts socio-économiques

Production

Revenus et coûts

Autres impacts socio-économiques

Impacts socioculturels

Impacts écologiques

Cycle de l'eau/ ruissellement

Sols

Biodiversité: végétale, animale

Réduction des risques de catastrophe et des risques climatiques

6.2 Impacts hors site que la Technologie a montrés

6.3 Exposition et sensibilité de la Technologie aux changements progressifs et aux évènements extrêmes/catastrophes liés au climat (telles que perçues par les exploitants des terres)

Changements climatiques progressifs

Changements climatiques progressifs

	Saison	Type de changements/ extrêmes climatiques	Comment la Technologie fait-elle face à cela?
températures annuelles		augmente	bien

Extrêmes climatiques (catastrophes)

Catastrophes météorologiques

	Comment la Technologie fait-elle face à cela?
pluie torrentielle locale	bien
tempête de vent locale	bien

Catastrophes climatiques

	Comment la Technologie fait-elle face à cela?
sécheresse	bien

Catastrophes hydrologiques

	Comment la Technologie fait-elle face à cela?
inondation générale (rivière)	bien

Autres conséquences liées au climat

Autres conséquences liées au climat

	Comment la Technologie fait-elle face à cela?
réduction de la période de croissance	pas connu

6.4 Analyse coûts-bénéfices

Quels sont les bénéfices comparativement aux coûts de mise en place (du point de vue des exploitants des terres)?

Quels sont les bénéfices comparativement aux coûts d'entretien récurrents (du point de vue des exploitants des terres)?

Commentaires:

The benefits will be visible in the longer time frame. There will be benefits of the investments when considering sea level rise in the upcoming 100 years.

6.5 Adoption de la Technologie

Commentaires:

Comments on spontaneous adoption: The SLM Technology is not implemented by local land users but this SLM technology needs to be implemented by spatial planning of the county / federal state.

There is a little trend towards spontaneous adoption of the Technology

Comments on adoption trend: The SLM Technology is not yet implemented by land users but first it needs to be considered in spatial planning of the county and the federal state. Land users and local experts showed during participatory workshops that there may be a chance for implementation.

6.7 Points forts/ avantages/ possibilités de la Technologie

Points forts/ avantages/ possibilités du point de vue de l'exploitant des terres

Protection of vulnerable landscape by building the retention area in the low elevated parts of the landscape that are up to date already difficult to drain. The retention area will support the drainage of the arable fields and pastures outside the retention area. How can they be sustained / enhanced? Combine with other technical solutions for protection against flooding (including strengthening of the ditch system and in-creasing pumping capacity).

Points forts/ avantages/ possibilités du point de vue du compilateur ou d'une autre personne ressource clé
Prevention of flooding during strong rainfalls and possibility to irrigate during dry periods How can they be sustained / enhanced? The larger the retention areas are the more water can be stored.
Prevention of salt water intrusion in the region. Fresh water in the retention areas prevent saline ground water from up dwelling How can they be sustained / enhanced? Build polders where saline ground water dwells up.
Endangered species might obtain new habitats in the retention area How can they be sustained / enhanced? Cessation of agricultural land use can help to improve the habitats for endangered species and increase attractiveness for tourism.
Through investments in building retention areas the very expensive strengthening of existing drainage structures is not necessary anymore How can they be sustained / enhanced? Alternative benefits for land owner can be generated e.g. increas-ing the attractiveness for tourism.

6.8 Faiblesses/ inconvénients/ risques de la Technologie et moyens de les surmonter

Faiblesses/ inconvénients/ risques du point de vue de l’exploitant des terres	Comment peuvent-ils être surmontés?
Retention area in a region of high relevance for tourism. The retention area will change the landscape and this may reduce the value of the region for tourism	Include interests from tourism in the retention area (access, information, attractivity).
Endangered species might lose habitats when establishing the retention polders	Do not build a retention area where endangered species live.
Loss of livelihoods	Retention areas should be planned for parts of the landscape without settlements.

Faiblesses/ inconvénients/ risques du point de vue du compilateur ou d'une autre personne ressource clé	Comment peuvent-ils être surmontés?
Loss of land for agricultural production	Build up retention area in low elevated parts, where the productivity is already poor.
For peat formation wet conditions are necessary, but under wet conditions highest methane emissions were measured. The emissions due to methane are therefore higher than the potential storage effects due to carbon sequestration.	Ground water levels should kept stable near to the soil surface.

7.2 Références des publications disponibles

Titre, auteur, année, ISBN:

http://www.comtess.uni-oldenburg.de/

7.3 Liens vers les informations pertinentes disponibles en ligne

Titre/ description:

http://www.comtess.uni-oldenburg.de/