Polder management near Altenheim, Germany

General

National Id:

Germany 02 light

Site name:

Polder Altenheim

Summary:

Ecological flooding has been introduced in a polder area next to the Rhine, near Altenheim in Germany. This measure improved the ecological functionality of the area, and created at the same time valuable space for recreation. Issues of forest management, a rising groundwater level and an increased mosquito population had to be dealt with.

NUTS Code:

Freiburg

RBD code:

DE2000

Transboundary:

Data provider:

Sabine Tutte, ACTeon

Source(s):

Auswirkungen der ökologischen Flutungen der Polder Altenheim

The Integrated Rhine Programme, flood control and restoration of former floodplains along the upper rhine

Integrated Rhine Programme Baden Wurtemberg

NWRM(s) implemented in the case study:

Floodplain restoration and management

Restoration and reconnection of seasonal streams

Reconnection of oxbow lakes and similar features

Forest riparian buffers

Re-naturalisation of polder areas

Longitude:

7.809403

Latitude:

48.464318

Site information

Climate zone:

cool temperate dry

Mean rainfall:

800

Mean rainfall unit:

mm/year

Average temperature:

9,5

Mean runoff:

1060

Mean runoff unit:

600 - 750 mm

Type:

Actual Test Site

Light or indepth?:

Light

Average slope range:

0-1%

Monitoring maintenance

Monitoring impacts effects:

Monitoring location:

In-Stream

Administrative annual costs:

100000

Administrative annual cost information:

The Regional Council hopes that this number will decrease sooner or later due to new knowledge.

Monitoring parameters:

Inside the polder several parameters were monitored to document the impact of ecological flooding on water and matter balance, state of groundwater, water courses and lakes, soil and biodiversity. Moreover, the water retention during flood events was documented.

Performance

Performance impact estimation method:

Catchment outlet

Performance impact estimation information:

The amount of terrestrial plants and the domination of single species in different vegetation layers was determined by rough assuming. Aquatic macrophytes were documented by the estimation method of Kohler and Janauer. Beetles were counted by pitfalls, the diversity of birds was determined by observing and counting nests.

Biophysical impacts

Information on increased water storage:

The water is stored in watercourses inside the polder and in case of retention also in the forest.

Information on runoff reduction:

No data available.

Information on Peak flow rate reduction:

During the last flood on the Upper Rhine in the 90's, the water retention inside the polder led to a reduction of the gauge of 24 cm and avoided thus the inondation of important industrial cities (Karlsruhe, Speyer, Mannheim).

Information on Increased groundwater level:

Ecological Flooding leads to rising groundwater levels outisde the polder that can affect property. Therfore a complex drainage system including channels, wells,lakes and pumping stations was created.

Information on Restoring hydraulic connections:

In order to distribute evenly water inside the polder, a system of water courses was reconnected and restored, the so called Schluten

Water quality overall improvements:

Negative impact-WQ deterioration

Information on Water quality overall improvements:

Measurements have shown that the overall water quality of the Rhine deteriorates when the water passes the polder. However, no danger for the drinking water supply exists.

Soil quality overall soil improvements:

Positive impact-SQ improvement

Information on Soil quality overall soil improvements:

Due to ecological flooding, the forest soil is constantly enriched by organic sediments serving as fertilizer for the plants.

Lessons, risks, implications...

Key lessons:

It is possible to adapt and modify the ecosystem inside a polder to water retention events by ecological flooding. Due to the measures the polder became a valuable recreational area for the citizens of the neighboring community. However, expensive protection measures for Altenheim are needed to avoid damage by rising groundwater level in consequence of ecological flooding.

Financing mechanism:

Financing mechanism information:

Land owners receive 20% of the value of their lot as compensation. In return, the regional council enters the title register in order to ensure that the lot can be used for flood protection even when the owner changes. Forest owners receive once a compensation. It would be difficult to discuss after every flood which damages on trees are recent or old. Since damages on fields happen only in the vegetation period, experts estimate after every inundation the damage. Afterwards the farmers are compensated.

Financing difficulties:

Success factor(s):

Type	Role	Comments
Attitude of decision makers	main factor	The regional council had to meet many restrictions (international contracts, lack of space). Nevertheless, they created with the polder Altenheim an example for the whole Integrated Rhine Programme (IRP) showing that ecological flooding works and that a polder area has multiple benefits.
Attitude of relevant stakeholders	secondary factor	One argument against ecological flooding is the fear of people towards a mosquito pest. Several communities formed a tasked force (the KABS), which is controling the mosquito population. This programme is very complex but effective.
Financing possibilities	main factor	The maintenance of a polder is very expensive. The international importance of the project enabled the mobilisation of sufficient funds.

Financing:

Type	Comments
National funds	0.415
Sub-national funds	0.585

Barrier:

Type	Role	Comments
Legal obligations / restrictions	main barrier	Ecological flooding does not reach the entire polder area. The good functioning of hydropower plants has priority. As a consequence, the flooding process depends on the Rhine discharge.
Other	secondary barrier	During ecological flooding, humans have to be kept out of the area and its surroundings. During the first test ecological flooding, animals could not escape from the polder area, as they were scared by the humans which were watching on the dykes. Many deers drowned in the flood that was hyped by German tabloids as scandal. The principle and usefulness of ecological flooding is often not understood by citizens. On other planned retention areas (polder Schwanau) of the Integrated Rhine Programme communities went to court against the state of Baden Wurtemberg. They fear for example that rising groundwater levels could damage their houses, or that dirty Rhine water could affect the drinking water aquifer.

Driver:

Type	Role	Comments
Legal obligations	main driver	A sudden inondation of the polder would have caused a severe impact on the ecosystem. According to law, impacts have to be avoided, minimised or balanced. This led to the development of the ecological flooding concept.
Legal obligations	secondary driver	Determines the amount of ecological flooding depending on the Rhine discharge.

Financing share:

Share type	Share	Comments
National funds	100	100% see above. 41,5% provided by the Federal Republic of Germany and 58,5% payed by the state of Baden-Württemberg. The total costs of the IRP are 1,3 billion €.

Socio-economic

Direct benefits information:

Lease of land around the swimming lake.

Ancillary benefits information:

Recreational value since the polder area is used for hiking, jogging, cycling and canoeing.

Costs investment information:

The adaptation of the forest was "cost neutral" since the community of Altenheim used the money received by the state as compensation to place funds and the interests are invested into forestry.

Costs capital:

1300000000

Costs capital information:

This money had to be invested for the 13 retention areas of the Integrated Rhine Programme.

Costs operation maintenance:

450000

Costs operation maintenance:

Upkeeping costs per retention area. This depends on the length of the dykes, the number of pumping stations, the length of streets inside the polder etc.

Costs total:

700000

Compensations annual information:

Every landowner inside the polder receives 20% of the land value as compensation. In return the Regional Council Freiburg enters to the title register. Forest owners are compensated once, since it is too complex to discuss after every flooding whether damages are new or old. After flooding events experts assume the damage happen on fields and the farmers are compensated individually

Ecosystem improved biodiversity:

Information on Ecosystem improved biodiversity:

Due to ecological flooding alluvial plant and animal communities could be established. The floods diversify the water courses which thus became habitat of different invertebrate and fish species. Several groundbeetle and dragonfly species came back to the new established alluvial forest. However, the regular flood events are source of mosquito pests that require a treatment by the members of a taskforce.

Ecosystem provisioning services:

Ecosystem impact climate regulation:

No information available

Policy, general governance and design targets

Policy description:

Physical alteration of the channel, the river bed and the floodplain due to hydropower plants, flood protection and an easier navigability on the Rhine.

Part of wider plan:

Policy pressure:

Policy requirement directive:

Policy impact:

Policy wider plan:

Wider plan type	Wider plan focus	Name	Comments
		Integrated Rhine Programme	The main focus of this programme is flood protection by restoring the floodplain on the upper Rhine upstream of Karlsruhe.

Policy area:

Policy target:

Target purpose
Peak-flow reduction
Increase Water Storage
Improved Biodiversity

Design & implementations

Application scale:

Field Scale

Installation date:

1987

Age:

Performance timescale:

Immediate

Area (ha):

520

Area subject to Land use change or Management/Practice change (ha):

520

Design capacity description:

17.6 Mio m³

Basis of design:

Use for retention approx. every 10 years.

Inflow volume:

Inflow volume unit:

m3/sec

Peak flow rate:

150

Public consultation:

Design contractual arrangement:

Arrangement type	Role	Responsibility	Name	Comments
Contractual agreement		Responsible	Treaty of Versailles	Treaty between France and Germany allowing France using the Rhine for Hydropower. Due to the construction of numerous dams the Rhine lost 90% of its floodplain and made the integrated rhine programme necessary
Organisational arrangement		Supporting	Comission for the Protection of The Rhine	The riparian countries of the Rhine formed this comission to improve the water quality and the overall ecological state of the river. Navigability is moreover an important issue

Design consultation activity:

Activity stage	Name	Key issues	Comments
Implementation phase	Information evenings		Since the ecological flooding is a quite new concept publicity has to be done in order that neighboring communities accept it. This has to be done continously. The polder Altenheim is a good exemple that shall calm down the worries of other communities were a polder shall be constructed
Other	site visits

Design land use change:

Design authority:

Authority type	Role	Name	Comments
NGO	Initiation of the measure	Environmental NGOs	Supporter of the ecological flooding approach
Other	Other	District Council	Approval of the measures
Other	Other	Community of Neuried	Member of the Mosquito fighting task force
Other	Determination of design details of the measure	Regional Council Freiburg	The Regional Council Freiburg is a sub division of the Ministry of the Environment in Baden Wurtemberg. It was in charge of the planning and design of the measures, as well as of the publicity
Forest owners	Other	Forest owners	Needed planning reliability and supported therefore the ecological flooding approach

Last updated: 22 Apr 2015 | Top

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Polder management near Altenheim, Germany

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