Flood detention basin (HRB) Ickern-Mengede

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Location: 51° 34' 59", 7° 21' 27"
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Project overview

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Status Complete
Project web site
Themes Habitat and biodiversity, Hydromorphology
Country Germany
Main contact forename Mechthild
Main contact surname Semrau
Main contact user ID User:EGLV
Contact organisation Emschergenossenschaft
Contact organisation web site http://eglv.de
Partner organisations
Parent multi-site project
This is a parent project
encompassing the following
projects
No
Aerial view of the HRB Ickern-Mengede during construction

Project summary

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Part of the integrated river basin management for the Emscher Region (865 km2, 2.700 inhabitants/ km2) is the revitalization of the river Emscher and its tributaries. Due to industrialization the waterbodies were systematically developed as open wastewater sewers in the beginning of the 20th century. Economic and technical alternatives such as closed sewer systems could not be implemented due to constant subsidence caused by coal mining. Momentarily, the river system is being restructured in order to enable the Emscher to once again be a fully functioning, continuous water-based ecosystem with typical topology and vegetation. An ecological concept based on the assumption of a non-interrupted river as a connection from the source to the mouth has been developed.

Studies on the feasibility of restructuring the Emscher show, that due to coal mining, industrial impacts and population changes the “original” conditions can never be reached again. It will not be possible to return the Emscher to its original, meandering state. Therefore, the reference conditions are no direct goals for the river restoration, but they give orientation in the planning procedure. One of the first hot spots that has been put into practice is the HRB Ickern-Mengede. The HRB comprises an area of 30 ha, where a typical lowland river with natural substrats, features and vegetation can be formed. A varied mosaic of biotopes, which are typical for floodplains (alder floodplain forest, sedge, typha and phragmites reed, floodgrass and potamogeton) is expected to develop. Most importantly, the basin can hold a volume of 1,1 km3 to protect the downstream riparian communities. After the ecological restoration of the Emscher basin, it won't be able to discharge floods as quickly, hence the upstream flood protection must be enhanced. Two million m3 of native soil had to be excavated. 450 000 m3 of this have been used to build a landscape monument between the basin and the close highway, thereby reducing noise pollution for the inhabitants of the basin and the close area. It has also been made accessible for the public as a lookout.

The river Emscher will be integrated into the basin, hence even smaller floods will reach the floodplain that has been created. Parts of the basin will be flooded about 80 days a year. Since the bottom of the HRB is uneven, parts of it will constantly be a body of standing water, whereas some elevated parts will be islands even during high floods. This diversity of topologic forms will lead to a great diversity in habitats - and therefore species.

As of now, the basin is still divided into three smaller parts by the dyked Emscher, because it needs to be separated from the wastewater which the Emscher is still carrying. Only during high floods diluted wastewater will run over the dykes to flood the basins. Once the wastewater is fully removed from the river, there will be a slight remodelling of the basins (removal of the dykes), thus creating the possibility for the river to mold its own body and have access to the floodplain.

Public participation process during the planning phase, 2006 a public workshop was organised by the EG on the design aspects of the construction (e.g. bike trails).

Monitoring surveys and results

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Lessons learnt

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Image gallery


View on one of the basins
View into basin nr. 2, with deadwood and Salix spec. visible
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Catchment and subcatchment

Catchment

River basin district Rhine
River basin Rhine

Subcatchment

River name Emscher
Area category
Area (km2) 865
865 km²
86,500 ha
Maximum altitude category
Maximum altitude (m)
Dominant geology quarternary, holocene
Ecoregion Central Plains
Dominant land cover Urban, Intensive agriculture (arable), Grassland, Broadleaf/mixed woodland (semi natural)
Waterbody ID DE_NRW_2772



Other case studies in this subcatchment: Upper Emscher


Site

Name HRB Ickern-Mengede
WFD water body codes DE_NRW_2772_O
WFD (national) typology Type 15: small sand-dominated lowland river
WFD water body name Emscher
Pre-project morphology Artificial bed, Over deepened, Straightened, Single channel
Reference morphology Actively meandering
Desired post project morphology Actively meandering, Set back defence
Heavily modified water body Yes
National/international site designation
Local/regional site designations
Protected species present Yes
Invasive species present Yes
Species of interest
Dominant hydrology Groundwater, Quick run-off
Dominant substrate Sand, Silt
River corridor land use Urban, Broadleaf/mixed woodland (semi natural), Improved/semi-improved grassland/pasture, Intensive agriculture (arable)
Average bankfull channel width category 5 - 10 m
Average bankfull channel width (m)
Average bankfull channel depth category 0.5 - 2 m
Average bankfull channel depth (m)
Mean discharge category
Mean annual discharge (m3/s)
Average channel gradient category Less than 0.001
Average channel gradient
Average unit stream power (W/m2)


Project background

Reach length directly affected (m)
Project started 2005/01/01
Works started 2010/01/01
Works completed 2013/12/31
Project completed
Total cost category more than 10000 k€
Total cost (k€) 62000
62,000 k€
62,000,000 €
Benefit to cost ratio
Funding sources

Cost for project phases

Phase cost category cost exact (k€) Lead organisation Contact forename Contact surname
Investigation and design Emschergenossenschaft
Stakeholder engagement and communication Emschergenossenschaft
Works and works supervision more than 10000 k€ 43700
43,700 k€
43,700,000 €
Emschergenossenschaft
Post-project management and maintenance Emschergenossenschaft
Monitoring Emschergenossenschaft



Reasons for river restoration

Mitigation of a pressure
Hydromorphology development of typical structures for the river and the riparian zone
Biology Create a new natural habitat with continuity for benthos, fishes and other organisms
Physico-chemical
Other reasons for the project Ensuring flood protection, development of an ecological hot spot, landscape enhancement


Measures

Structural measures
Bank/bed modifications removal of bottom slab formwork, Adding sinuosity
Floodplain / River corridor Increase water retention area, Connection to wider floodplain, Wetland habitat
Planform / Channel pattern Channel naturalisation, Improvement of channel morphology, Enabling dynamics, Meandering channel
Other
Non-structural measures
Management interventions
Social measures (incl. engagement) Community involvement
Other


Monitoring

Hydromorphological quality elements

Element When monitored Type of monitoring Control site used Result
Before measures After measures Qualitative Quantitative
Structure & condition of riparian/lake shore zones No Yes Yes No No Awaiting results
Channel pattern/planform No Yes Yes No No Awaiting results
Width & depth variation No Yes Yes No No Awaiting results

Biological quality elements

Element When monitored Type of monitoring Control site used Result
Before measures After measures Qualitative Quantitative
Invertebrates No Yes Yes Yes No Awaiting results
Fish No Yes Yes Yes No Awaiting results
Macrophytes No Yes Yes No No Awaiting results

Physico-chemical quality elements

Element When monitored Type of monitoring Control site used Result
Before measures After measures Qualitative Quantitative
Nutrient concentrations Yes Yes Yes Yes No Awaiting results
Oxygen balance Yes Yes Yes Yes No Awaiting results
PH Yes Yes Yes Yes No Awaiting results
Salinity Yes Yes Yes Yes No Awaiting results
Temperature Yes Yes Yes Yes No Awaiting results


Any other monitoring, e.g. social, economic

Element When monitored Type of monitoring Control site used Result
Before measures After measures Qualitative Quantitative


Monitoring documents



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Additional links and references

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Supplementary Information

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