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
0
Data provider
Sabine Tutte, ACTeon
Source(s)
NWRM(s) implemented in the case study
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
1
Monitoring location
In-Stream
Administrative annual costs
100000
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.
Design & implementations
Application scale
Field Scale
Installation date
1987
Age
27
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
40
Inflow volume unit
m3/sec
Peak flow rate
150
Public consultation
1
Design contractual arrangement
| Arrangement type | Responsibility | Role | Comments | Name | |
|---|---|---|---|---|---|
|
Contractual agreement
|
Responsible
|
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
|
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|
Organisational arrangement
|
Supporting
|
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
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Other
|
site visits
|
Design land use change
| Land use change type |
|---|
Design authority
| Authority type | Role | Responsibility | Name | Comments | |
|---|---|---|---|---|---|
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
1
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
0
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. |
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|
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
| Financing type | Comments | |
|---|---|---|
|
National funds
|
0.415
|
|
|
Sub-national funds
|
0.585
|
Driver
| 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.
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|
|
Legal obligations
|
secondary driver
|
Determines the amount of ecological flooding depending on the Rhine discharge.
|
Financing share
| Financing share type | Share | Comments | |
|---|---|---|---|
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
1
Policy target
| Target purpose | |
|---|---|
|
Increase Water Storage
|
|
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Peak-flow reduction
|
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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 |
|---|
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
1
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
0
Ecosystem impact climate regulation
No information available
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.
