1.2 Contact details of resource persons and institutions involved in the assessment and documentation of the Technology

Name of project which facilitated the documentation/ evaluation of the Technology (if relevant)

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

Name of the institution(s) which facilitated the documentation/ evaluation of the Technology (if relevant)

University of Oldenburg (University of Oldenburg) - Germany

1.3 Conditions regarding the use of data documented through WOCAT

When were the data compiled (in the field)?

09/06/2015

The compiler and key resource person(s) accept the conditions regarding the use of data documented through WOCAT:

Yes

2.1 Short description of the Technology

Definition of the Technology:

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 Detailed description of the Technology

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 of the Technology

2.5 Country/ region/ locations where the Technology has been applied and which are covered by this assessment

2.6 Date of implementation

If precise year is not known, indicate approximate date:

• 10-50 years ago

2.7 Introduction of the Technology

Specify how the Technology was introduced:

• during experiments/ research
• through projects/ external interventions

3.2 Current land use type(s) where the Technology is applied

Comments:

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

If land use has changed due to the implementation of the Technology, indicate land use before implementation of the Technology:

Mixed: Mp: Agro-pastoralism

3.3 Further information about land use

Comments:

Water supply: rainfed, mixed rainfed - irrigated

Number of growing seasons per year:

• 1

Specify:

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

Livestock density (if relevant):

> 100 LU /km2

3.4 SLM group to which the Technology belongs

• surface water management (spring, river, lakes, sea)
• wetland protection/ management

• Flood prevention

3.5 Spread of the Technology

Comments:

Total area covered by the SLM Technology is 33.7 m2.

3.6 SLM measures comprising the Technology

Comments:

Main measures: structural measures

Secondary measures: management measures

3.7 Main types of land degradation addressed by the Technology

Comments:

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 Prevention, reduction, or restoration of land degradation

Specify the goal of the Technology with regard to land degradation:

• prevent land degradation
• reduce land degradation

Comments:

Main goals: prevention of land degradation

Secondary goals: mitigation / reduction of land degradation

4.1 Technical drawing of the Technology

4.2 Technical specifications/ explanations of technical drawing

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 General information regarding the calculation of inputs and costs

other/ national currency (specify):

Euro

Indicate exchange rate from USD to local currency (if relevant): 1 USD =:

0.94

4.4 Establishment activities

	Activity	Type of measure	Timing
1.	Building of dams	Structural	during winter months

4.5 Costs and inputs needed for establishment

	Specify input	Unit	Quantity	Costs per Unit	Total costs per input	% of costs borne by land users
Labour	Labour	Dam	1.0	21000000.0	21000000.0
Equipment	Machine use	Dam	1.0	9000000.0	9000000.0
Construction material	Earth	Dam	1.0	750000.0	750000.0
Total costs for establishment of the Technology					30750000.0

Comments:

Duration of establishment phase: 3 month(s)

4.6 Maintenance/ recurrent activities

	Activity	Type of measure	Timing/ frequency
1.	Control of dams	Structural	once a year
2.	Maintenance of dams	Structural	once a year
3.	Maintanance of drainage system	Structural	once a year

4.7 Costs and inputs needed for maintenance/ recurrent activities (per year)

	Specify input	Unit	Quantity	Costs per Unit	Total costs per input	% of costs borne by land users
Labour	Labour	Dam	1.0	800.0	800.0
Equipment	Machine use	Dam	1.0	300.0	300.0
Construction material	Earth	Dam	1.0	100.0	100.0	1.0
Other	Maintenance per km ditch	Dam	1.0	2270.7	2270.7
Total costs for maintenance of the Technology					3470.7

Comments:

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 Most important factors affecting the costs

Describe the most determinate factors affecting the costs:

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 Climate

5.2 Topography

5.3 Soils

If available, attach full soil description or specify the available information, e.g. soil type, soil PH/ acidity, Cation Exchange Capacity, nitrogen, salinity etc.

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

5.4 Water availability and quality

5.5 Biodiversity

5.6 Characteristics of land users applying the Technology

Indicate other relevant characteristics of the land users:

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 Average area of land owned or leased by land users applying the Technology

5.8 Land ownership, land use rights, and water use rights

Land ownership:

• individual, not titled

Land use rights:

• individual

5.9 Access to services and infrastructure

6.1 On-site impacts the Technology has shown

Socio-economic impacts

Production

Income and costs

Other socio-economic impacts

Socio-cultural impacts

Ecological impacts

Water cycle/ runoff

Soil

Biodiversity: vegetation, animals

Climate and disaster risk reduction

6.2 Off-site impacts the Technology has shown

6.3 Exposure and sensitivity of the Technology to gradual climate change and climate-related extremes/ disasters (as perceived by land users)

Gradual climate change

Gradual climate change

	Season	Type of climatic change/ extreme	How does the Technology cope with it?
annual temperature		increase	well

Climate-related extremes (disasters)

Meteorological disasters

	How does the Technology cope with it?
local rainstorm	well
local windstorm	well

Climatological disasters

	How does the Technology cope with it?
drought	well

Hydrological disasters

	How does the Technology cope with it?
general (river) flood	well

Other climate-related consequences

Other climate-related consequences

	How does the Technology cope with it?
reduced growing period	not known

6.4 Cost-benefit analysis

How do the benefits compare with the establishment costs (from land users’ perspective)?

How do the benefits compare with the maintenance/ recurrent costs (from land users' perspective)?

Comments:

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 of the Technology

Comments:

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 Strengths/ advantages/ opportunities of the Technology

Strengths/ advantages/ opportunities in the land user’s view

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).

Strengths/ advantages/ opportunities in the compiler’s or other key resource person’s view
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 Weaknesses/ disadvantages/ risks of the Technology and ways of overcoming them

Weaknesses/ disadvantages/ risks in the land user’s view	How can they be overcome?
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.

Weaknesses/ disadvantages/ risks in the compiler’s or other key resource person’s view	How can they be overcome?
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 References to available publications

Title, author, year, ISBN:

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

7.3 Links to relevant information which is available online

Title/ description:

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