Case study:Voorste Nete at Dessel

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Location: 51° 13' 56", 5° 9' 1"
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Project overview

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Status Complete
Project web site
Themes Fisheries, Habitat and biodiversity, Hydromorphology, Monitoring
Country Belgium
Main contact forename Nick
Main contact surname Elbourne
Main contact user ID User:NickRRC
Contact organisation River Restoration Centre
Contact organisation web site http://www.therrc.co.uk
Partner organisations University Hasselt, Centre for Environmental Sciences, Diepenbeek
Parent multi-site project
This is a parent project
encompassing the following
projects
No
Source of photographs - ECRR 2008. Upper row (left and right): original reach of the Voorste Nete. Middle row (left and right): Excavation of a 5 m wide stretch for placing the bentonite mat and refilling with the original sand. Bottom row (left and right): Diverted reach of the Voorste Nete, dug out in sand filled bentonite lining with transferred substrate from the original reach, and the same stretch 6 months later during first monitoring showing the changes in dimensions caused by a summer storm in 2004.

Project summary

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In 2004 a reach of 1.3km of the small, channelized lowland brook, Voorste Nete, was diverted because of sand mining activities. The sinuosity of the newly created reach of the Voorste Nete, 1.9km in length, was based on old maps, aerial photography and field measurements. The new brook was hydrologically isolated with a bentonite mat preventing water loss due to a decline of the groundwater level. The sides of the bentonite were placed upright for 0.5m and the lining was filled with the original sand from digging out the new reach.

Originally the newly created streambed has a weak meandering channel pattern (sinuoscity 1.1), and was 1m wide at the bottom and 2m wide at the top. In August 2004, a summer storm caused severe erosion and had a noticeable impact on the profile. In the first three years, mechanical weed clearance was only conducted once in the upstream reach of the diversion in autumn 2005. In 2007, mechanical weed mowing was executed for the total stream.

Monitoring surveys and results

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Lessons learnt

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Catchment and subcatchment

Catchment

River basin district Meuse
River basin Meuse

Subcatchment

River name Meuse
Area category more than 10000 km²
Area (km2) 465
465 km²
46,500 ha
Maximum altitude category 100 - 200 m
Maximum altitude (m) 200
200 m
0.2 km
20,000 cm
Dominant geology chalk and loess
Ecoregion Western Plains
Dominant land cover Intensive agriculture, Urban
Waterbody ID



Other case studies in this subcatchment: Aaijen- Removal of bank fixation, Meers - Floodplain lowering, Reméandration du Geer à Grand-Axhe, Rijkelse Bemden - River bed widening, Tungelroyse beek


Site

Name Voorste Nete
WFD water body codes
WFD (national) typology
WFD water body name
Pre-project morphology
Reference morphology
Desired post project morphology
Heavily modified water body No
National/international site designation
Local/regional site designations
Protected species present Yes
Invasive species present No
Species of interest Spined loach, Three-spined stickelback, Nine-spined stickelback, Gudgeon, European eel (Anguilla anguilla)
Dominant hydrology
Dominant substrate
River corridor land use Intensive agriculture (arable)
Average bankfull channel width category 2 - 5 m
Average bankfull channel width (m) 2
2 m
0.002 km
200 cm
Average bankfull channel depth category
Average bankfull channel depth (m)
Mean discharge category 0.1 - 1.0 m³/s
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) 1900
1,900 m
1.9 km
190,000 cm
Project started 2004/04/01
Works started 2004/04/01
Works completed 2004/06/01
Project completed 2004/06/01
Total cost category
Total cost (k€)
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
Post-project management and maintenance
Monitoring University Hasselt Alain De Vocht



Reasons for river restoration

Mitigation of a pressure Aggregate/mineral extraction
Hydromorphology Channel pattern/planform, Width & depth variation, Substrate conditions, Quantity & dynamics of flow
Biology Fish: Species composition, Fish: Age structure, Fish: Abundance, Invertebrates: Taxonomic composition
Physico-chemical Oxygen balance
Other reasons for the project


Measures

Structural measures
Bank/bed modifications Translocation of original substrate into new channel, Alteration in channel dimensions
Floodplain / River corridor
Planform / Channel pattern Channel naturalisation, Meandering channel
Other
Non-structural measures
Management interventions Weed clearance
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
Invertebrates Yes Yes No Yes Yes Improvement
Macrophytes Yes Yes No Yes Yes Improvement
Angiosperms Yes Yes No Yes Yes Improvement
Fish: Species composition Yes Yes No Yes Yes No change
Fish: Abundance Yes Yes No Yes Yes Improvement

Physico-chemical quality elements

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

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



Additional documents and videos


Additional links and references

Link Description
http://www.ecrr.org/archive/conf08/pdf/proceed10.pdf De Vocht et al. (2008) Ecological Evaluation of a Technically Restored Lowland Watercourse in Flanders, Belgium, p.583-592.

Supplementary Information

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