Case study:Bio-engineering and creation of side channels along the rectified section of the Scarpe River in Arras

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Location: 50° 17' 28", 2° 46' 39"
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Project overview

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Status Complete
Project web site
Themes Habitat and biodiversity, Water quality
Country France
Main contact forename Nathalie
Main contact surname Bret
Main contact user ID
Contact organisation
Contact organisation web site http://www.cu-arras.fr/
Partner organisations Artois-Picardie water agency; Pas-de-Artois-Picardie water agency; Pas-de-Calais departmental federation of certified associations for fishing and protection of aquatic environments (FDAAPPMA 62)departmental federation of certified associations for fishing and protection of aquatic environments (FDAAPPMA 62)
Parent multi-site project
This is a parent project
encompassing the following
projects
No
Creation of stagnant and semi-stagnant lagoons along the Scarpe. Summer 2010. (Communauté urbaine d’Arras)

Project summary

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In a partnership with the Artois-Picardie water agency, CUA launched ecological-restoration works on a section of the Scarpe. The reaches most affected by anthropogenic pressures were seen as the priority, namely the entire section between Arras and SaintLaurent-Blangy.

A study by a specialised consulting firm recommended restoring natural banks with a slight slope and improving the riparian vegetation.

The metal sheet piles, initially installed for bank protection, were deemed unsuitable and removed.

The banks were graded to a slight slope and stabilised using techniques suited to the hydraulic constraints weighing on each sector:

- helophyte rolls or calcareous landfill with geotextile fabric in areas where the constraints are not severe;

- mixed techniques (gabion bed and vegetated geomats) in areas subjected to greater constraints.

A total of 1 750 metres of bio-engineering bank-protection techniques were installed.

A number of measures were taken for the riparian vegetation, including planting of helophytes at the foot of banks, seeding of work areas with a mix of herbaceous plants, restoration of wooded areas by planting white willows and elimination of the invasive species found on site.

The top of the white willows was cut to encourage the growth of buds and of the tree trunks. This pruning technique will produce cavities that birds, small mammals and insects can use.

A lagoon was also created as an alluvial “annex” with two reed beds measuring 1 000 and 1 450 m² on the site of the former turn-around point for péniche barges in an effort to restore habitats for different species, notably pike.

Monitoring surveys and results

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An pre work survey was carried out in 2010,on the plant and animal compartments. Currently, no particular ecological monitoring has been set up. However, a check on the renewed growth of the vegetation was run in September 2012, during the works.

An assessment on the changes in the environment is also planned at some point at least five years after the works.

Unfortunately, the works had to be done from the water, which made it difficult. In addition, a large geese population, present on the river since before the works, has damaged and slowed the regrowth of the helophyte vegetation, particularly in the reed beds.

In 2010, the pre works assessment revealed a relictual population of woolly burdock that still existed on the site, but was threatened. The assessment was also an occasion to run surveys on two fish species, two emblematic bird species and one emblematic insect species. No amphibian species were noted.

An assessment of the impact of the works on the restored habitats and on biodiversity is planned at some point at least five years after the works in order to give enough time to the environment to adapt and to the various species to go through their life cycle. The assessment, carried out by a specialised consulting firm, will be based on the changes in the population numbers of the species listed in the initiallyt in order to determine the degree to which the objectives set by the project owner were met, namely:

- maintain the woolly burdock, pike and eel populations;

- install at least one amphibian species;

- double the number of bird and insect species (two and one respectively) observed prior to the works.

This project strove to achieve a balance between the ecological value of the site and its use as a waterway, i.e. a channel for commercial shipping, pleasure boating and the corresponding recreational activities. For example, the landscape of the site was improved with beneficial effects on tourism and pleasure boating, as well as on recreational activities (walking, etc.).

Lessons learnt

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Image gallery


Banks protected by sheet piles prior to the restoration works. Autumn 2010. (Communauté urbaine d’Arras).
Banks regraded and planted. Autumn 2012. (Communauté urbaine d’Arras).
Erosion and damage near the turn-around point on the Scarpe. Autumn 2010. (SOGREAH).
Regrading and creation of a reed bed by closing the turnaround point. Autumn 2012. (Communauté urbaine d’Arras).
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Catchment and subcatchment



Site

Name
WFD water body codes AR48
WFD (national) typology
WFD water body name
Pre-project morphology
Reference morphology
Desired post project morphology
Heavily modified water body Yes
National/international site designation
Local/regional site designations
Protected species present No
Invasive species present No
Species of interest
Dominant hydrology
Dominant substrate
River corridor land use
Average bankfull channel width category 10 - 50 m
Average bankfull channel width (m) 23
23 m
0.023 km
2,300 cm
Average bankfull channel depth category
Average bankfull channel depth (m)
Mean discharge category 1 - 10 m³/s
Mean annual discharge (m3/s) 3.2
3.2 m³/s
3,200 l/s
Average channel gradient category
Average channel gradient
Average unit stream power (W/m2)


Project background

Reach length directly affected (m) 1760
1,760 m
1.76 km
176,000 cm
Project started 2009/01/01
Works started
Works completed
Project completed 2012/01/01
Total cost category 1000 - 5000 k€
Total cost (k€) 1321
1,321 k€
1,321,000 €
Benefit to cost ratio
Funding sources Artois-Picardie water agency (51%), European Regional Development Fund (48%), Arras urban area (1%)

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



Reasons for river restoration

Mitigation of a pressure Riparian development
Hydromorphology
Biology Fish: Abundance, Fish: Species composition
Physico-chemical
Other reasons for the project Improve the biological and chemical quality of the Scarpe River, Recreate reproduction habitats for various species.


Measures

Structural measures
Bank/bed modifications Removal of metal sheet piles, installation of bio-engeneering bank protection, Helophytes planted, Installation of geotextile, Gabion bed
Floodplain / River corridor Planting of helophytes at the foot of banks, Seeding of work areas with a mix of herbaceous plant, restoration of wooded areas by planting white willows, Elimination of the invasive species found on site, Creation of pond
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

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.onema.fr/sites/default/files/pdf/afb rex r1 scarpe gb v3.pdf All information on this page is copied from AFB, The French Agency for biodiversity.

Supplementary Information

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