Polder management near Altenheim, Germany

National Id
Germany 02 light
Site name
Polder Altenheim
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.
RBD code
Data provider
Sabine Tutte, ACTeon
Climate zone
cool temperate dry
Mean rainfall
Mean rainfall unit
Average temperature
Mean runoff
Mean runoff unit
600 - 750 mm
Actual Test Site
Light or indepth?
Average slope range
Monitoring impacts effects
Monitoring location
Administrative annual costs
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 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.
Application scale
Field Scale
Installation date
Performance timescale
Area (ha)
Area subject to Land use change or Management/Practice change (ha)
Design capacity description
17.6 Mio m³
Basis of design
Use for retention approx. every 10 years.
Inflow volume
Inflow volume unit
Peak flow rate
Public consultation
Design contractual arrangement
Arrangement type Responsibility Role Comments Name
Contractual agreement
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
Treaty of Versailles
Organisational arrangement
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
Comission for the Protection of The Rhine
Design consultation activity
Activity stage Key issues Name 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
site visits
Design land use change
Land use change type
Design authority
Authority type Role Responsibility Name Comments
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
District Council
Approval of the measures
Community of Neuried
Member of the Mosquito fighting task force
Forest owners
Forest owners
Needed planning reliability and supported therefore the ecological flooding approach
Initiation of the measure
Environmental NGOs
Supporter of the ecological flooding approach
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)
Success factor type Success factor 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.

Financing possibilities
main factor

The maintenance of a polder is very expensive. The international importance of the project enabled the mobilisation of sufficient funds.

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 type Comments
National funds
Sub-national funds
Barrier type Barrier 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.
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 Driver 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
Financing share type Share Comments
National funds
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 €.
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 target
Target purpose
Increase Water Storage
Peak-flow reduction
Improved Biodiversity
Policy pressure
Pressure directive Relevant pressure
Policy area
Policy area type Policy area focus Name Comments
Policy impact
Impact directive Relevant 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 requirement directive
Requirement directive Specification
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
Costs capital information
This money had to be invested for the 13 retention areas of the Integrated Rhine Programme.
Costs operation maintenance
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
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
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.


Logos of all partners of NWRM project