Case study:Flood detention basin (HRB) Mengede

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Location: 51° 34' 58.57" N, 7° 21' 27.28" E
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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
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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, so that the Emscher will once again become 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 to realize is the HRB Mengede. The HRB will comprise 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. Two million m3 of native soil hav to be excavated. Half of which will be used to build dikes.

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Catchment and subcatchment

Catchment

River basin district Rhine
River basin Rhine

Subcatchment

River name Emscher
Area category
Area (km2) 865865 km² <br />86,500 ha <br />
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 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
Average bankfull channel width (m)
Average bankfull channel depth category
Average bankfull channel depth (m)
Mean discharge category
Mean annual discharge (m3/s)
Average channel gradient category
Average channel gradient
Average unit stream power (W/m2)


Project background

Reach length directly affected (m)
Project started
Works started 2010/01/01
Works completed 2013/12/31
Project completed
Total cost category more than 10000 k€
Total cost (k€) 6200062,000 k€ <br />62,000,000 € <br />
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
Stakeholder engagement and communication
Works and works supervision more than 10000 k€ 4370043,700 k€ <br />43,700,000 € <br />
Post-project management and maintenance
Monitoring



Reasons for river restoration

Mitigation of a pressure
Hydromorphology
Biology
Physico-chemical
Other reasons for the project


Measures

Structural measures
Bank/bed modifications
Floodplain / River corridor
Planform / Channel pattern
Other
Non-structural measures
Management interventions
Social measures (incl. engagement)
Other


Monitoring

Hydromorphological quality elements

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

Biological quality elements

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

Physico-chemical quality elements

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Any other monitoring, e.g. social, economic

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Monitoring documents



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Supplementary Information

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