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D
Les travaux ont consisté à démanteler les vantelleries
de huit ouvrages déjà ouverts répartis
sur le cours de l’Aa. Les radiers de fond et
les fi xations en berges ont volontairement été
conservés afi n de freiner les vitesses d’écoulement
et également d’éviter l’érosion régressive
en maintenant un point dur. Un 9e ouvrage
(Moulin Snick) n’a pas pu faire l’objet d’un effacement
en raison du risque potentiel d’érosion
régressive. Le seuil résiduel de 0,9 mètre
étant infranchissable, les vannes de l’ouvrage
ont été démantelées et une passe à poissons
a été aménagée en 2008. Cet aménagement
concilie les gains environnementaux et les aspects
patrimoniaux du site, la roue à aubes de
l’ouvrage ayant été conservée et demeurant
opérationnelle. +
A
Les travaux sont composés de deux grandes opérations:
d’une part, le reméandrage du Woigot sur un
linéaire d’un kilomètre en amont du plan d’eau et,
d’autre part, la création d’une rivière de contournement
en rive gauche du plan d’eau sur 1,1 km de long.
L’opération de vidange du plan d’eau se déroule en
deux phases. La première consiste à une vidange rapide.
Lors de la seconde, plus lente (sur deux jours),
un dispositif de ballots de paille est placé en aval des
ouvrages pour filtrer les eaux. Une fois secs, les sédiments
sont régalés sur deux zones du plan d’eau:
• en amont, de façon à créer une zone humide pour
diversifier les habitats et favoriser l’autoépuration
• en aval, sur la future zone de l’amphithéâtre de
verdure située en rive gauche.
Le barrage (clapet et digue de 92 m de long) a ensuite
été détruit et les matériaux réutilisés sur place
pour la construction de la nouvelle digue et de l’amphithéâtre
de verdure. Deux ouvrages viennent remplacer
l’ancien:
• en amont, un ouvrage de répartition des débits
équipé d’un pertuis et d’une passe à poissons
• une digue latérale de 1 100 m avec, en aval, un ouvrage
maçonné permettant de réguler les débits de
sortie.
Le nouveau lit est créé en rive gauche du plan d’eau,
d’une pente moyenne de 3,8 ‰. Les berges, sur ce
nouveau lit, sont stabilisées par du génie végétal.
En aval du plan d’eau, le seuil de Caulre (hauteur de
chute de 4 m) est remplacé par une passe à poissons
composée de seize rangées de blocs franchissables par
conception. En amont du plan d’eau, le seuil de Bonnes
Fontaines (hauteur de chute de 1,1 m) est dérasé.
Le Woigot est taluté sur 1 000 m en amont du plan
d’eau pour retrouver un cours d’eau sinueux avec un
lit naturel d’une largeur de deux mètres (largeur de
neuf mètres avant travaux). Les berges sont maintenues
si nécessaire par du génie végétal et une ripisylve
est plantée le long de la berge. +
D
Dérivation et recréation du lit mineur du ruisseau de Bel Orient au droit de quatre plans d’eau à Gueltas +
Les travaux sont réalisés selon les étapes suivantes:
• installation d’un ouvrage de répartition et de moines
pour réserver le débit d’étiage vers le cours d’eau
• création d’un lit de contournement des plans d’eau
de 1 800 m côté ouest/nord-ouest (linéaire à créer
d’environ 900 m auxquels s’ajoutent 900 m d’anciens
fossés de drainage ou reliques de la construction des
plans d’eau). Le tracé est établi à partir du profil en
long, en créant des méandres utilisant les irrégularités
de terrain et respectant les plus gros arbres. Le
lit est surcreusé afin d’assurer un écoulement suffisant
tout en sécurisant la berge rive gauche, avec des
largeurs variant de 0,5 à 1,1 m. Il est ensuite étanchéifié
en rive gauche, à l’aide des terres argileuses
décaissées. Les fossés drainants sont comblés à l’aide
de matériaux argileux. Enfin, le lit du cours d’eau est
raccordé aux buses et aux ouvrages de répartition.
Les berges sont également protégées contre l’érosion
en amont et en aval de chaque ouvrage. Une
recharge en granulats ponctuelle est effectuée pour
établir des zones de reproduction de la truite
• vidange des trois étangs aval réalisée sur trois années
de 2009 à 2011
• réhabilitation du linéaire existant (fossé), au droit
de deux étangs, aval et amont, par aménagement de
risbermes minérales pour accentuer la sinuosité et
par recharges granulométriques sur plusieurs tronçons
pour stabiliser le lit et renforcer la rugosité sur
certains
• enfin, trois seuils devenus infranchissables, suite
à une forte érosion régressive, sont supprimés et
réaménagés. +
L
Levington Marina (Map 1) on the River Orwell in Suffolk is dredged each winter using a 10-foot cutter suction dredger to maintain water depths around the pontoons and berths. Since 2014, dredged material has been deposited in 2 beneficial placement schemes licensed by Defra and approved by Natural England. Each year 15,000–20,000m3 of silt is dredged and placed on the foreshore. Operations are carried out between mid-November and early April.
A Marine Management Organisation (MMO) licence is held by Suffolk Yacht Harbour for beneficial foreshore disposal. Dredged material is recovered as a slurry and conveyed by one of two fixed pipes to a deposition area east and west of the harbour where saltmarsh has been degraded and fragmented. The ends of the fixed pipes are moved each year to vary the location in which dredged material is discharged. Photo 1 shows the Levington Lagoon.
Coir rolls and wooden stakes have been introduced into the deposition areas to contribute to:
• retaining discharged material in place
• impede flow
• make it easier to deposit sediment during the dredging operation
Significant accretion of between 100mm and 300mm has been noted during the 3 years of monitoring. It is anticipated that this will translate into more robust growth of pioneer saltmarsh vegetation and in due course colonisation by high saltmarsh vegetation. +
Limestone Ribble Restoration is a partnership project that will use CRF funds to improve watercourses in an area of the Ribble Catchment that has been quarried, farmed and industrialised for hundreds of years. The degraded habitat, diffuse pollution and obstructions to fish passage are causing certain watercourses in this area to fail to meet the required standards under the Water Framework Directive (WFD).
Through restoration work, the project will address issues including: unnatural flow regimes caused by upland grips; sediment which has a direct adverse effect on water quality; barriers to fish migration, preventing fish from reaching habitat that modelling shows they should be present in; interrupted natural downstream movement of substrate which reduces spawning habitat for salmonids; fertiliser run off into rivers which can cause nutrient enrichment and impact negatively on river ecology; expected rise in river water temperature associated with climate change; failed bathing water standard in coastal reaches due to presence of excess pathogens attributable to upstream sources. +
Llangloffan Fen is a lowland wetland in the upper part of the Western Cleddau river SAC. The fen is a national nature reserve managed in parts by the Wildlife Trust of South and West Wales (WTSWW), Natural Resources Wales (NRW) and some private landowners.
Large wood was used to introduce habitat diversity and improve floodplain connectivity. +
B
Local Levy funding (~£350,000) was allocated by the North East Regional Flood and Coastal Committee (RFCC). The Environment Agency used ~£250,000 to commission Newcastle University to monitor the catchment, conduct hydraulic modelling, design run-off attenuation features (RAFs), engage with landowners and the community, and appoint specialist contractors to deliver the interventions. The remaining funds were used to repair a damaged wall on the bridge in Belford village and to improve the drainage network in the village. (Note that only 2 landowners were willing to take part at the early stages.)
Monitoring of individual RAFs has shown that they are able to have a significant impact (up to 10% reduction) on the flood peak in small to medium events, but that they were overwhelmed by larger events (by filling with floodwater during the rising limb of the hydrograph during observed storms). The RAFs have also provided multiple benefits including sediment capture and water quality improvements. +
K
Located upstream of Brothers Water in the Ullswater valley, Kirkstone Beck runs through the valley bottom at Hartsop Hall Farm. The beck, and its tributaries, had been subjected to significant modifications, straightened and with large embankments completely disconnecting the channel from the floodplain.
However, Hartsop Hall Farm is one of the few farms in the Lake District which still produces all its own silage and hay on-farm. With limited valley bottom land, every little bit of floodplain is therefore vital to the success of the farm business. In 2019 the National Trust’s Riverlands project, part of a national programme of river and catchment restoration work, began working closely with the tenant farmer to develop a river restoration design which allowed the development of natural processes within a confined area, protecting the meadows that are relied upon to feed livestock over winter. Other partners in the scheme design included the Environment Agency and Natural England.
An interest in potential change was triggered by Storm Desmond in 2015, during which the only access bridge to the farmstead was damaged and a novel solution was sought. After consultation with the tenant farmer to agree which bits of land could be given over to the river, the resulting design aimed for a continuous thread of restoration along ~2km of channel. The aims of the project were to restore natural processes to this length of river, improve the SSSI condition of Brothers Water immediately downstream of the restored reach, and deliver a sustainable, flood resilient access solution to the farmstead.
The project was delivered in 2022. Embankments were set back from the channel, retaining protection for the meadows but allowing the river much more space. T-junction style tributary confluences were restored to wide, wandering systems, and the narrow single-span bridge was replaced with a wider double-span crossing. In the fens of Brothers Water, the design took a process-led approach, blocking the existing channel with large woody debris to encourage the natural evolution of an anastomosing system across the delta.
Initial analysis shows that the total river area has increased significantly, from 1,850m2 to 23,300m2; that’s more than 12 times as much river habitat available post-restoration compared to the baseline. Considering the level of compromise required on this project, these figures are impressive. Furthermore, flood events since construction have seen dynamic changes throughout the restored areas, with channels shifting through three large boulder wandering sections (semi-permanent gravel bar consisting of larger, boulder-type material). Large areas of open standing water have also been created, adding an important habitat which is so often missing from the landscape.
C
London Wildlife Trust have undertaken meander reconnection works at Crane Meadows Nature Reserve in Cranford, Hounslow.
The meanders were cut off from the river over 100 years ago when the river was subject to heavy modifications. The London Borough of Hounslow and the Environment Agency had previously reconnected three meanders at the site. LWT's input now brings this total to five.
In addition to the meander connections a backwater area was created to improve the river's resilience to pollution events and to enhance habitat for juvenile coarse fish.
Aims of this Project
1. To increase morphological and flow diversity in the river channel leading to
better quality habitat for macrophytes and benthic invertebrates and improved
habitats for fish.
2. To decrease flow conveyance and increase water storage capacity,
contributing to the rivers hydrological response time being reduced during
periods of high flows.
3. To provide new back water areas for aquatic organisms to shelter from the
main flow of the river during times of disturbance, including pollution events.
4. To increase public awareness and appreciation of the issues affecting the
Crane Catchment and the techniques used to solve them via a volunteer
engagement programme.
A gravel riffle will be placed just downstream of the meander inflow to ensure all water flows through the meander when river levels are low.
The bund blocking the inflow of water to the meander will be removed. +
R
Longinoja brook has been restored several times during years 2006-2011. The straightened brook flows through densely populated area and partly along cultivated area. The brook is situated in the city of Helsinki. Longinoja brook is an important breeding area for the sea trout of the Vantaanjoki River. The aims of restorations was to create and increase the breeding possibilities for migrating fish and also to improve the area’s landscape. Restoration was part of the project where modern environmental hydraulic engineering methods were studied in the areas with fine-grained soils. The planning aimed to enhance natural conditions and at the same time maintain sufficient drainage level. The restoration project has been a good example of a succeeded co-operation between different organizations and stakeholders. The project was managed by the Finnish Environmental authorities (Finnish Environment Institute and The Centre for Economic Development, Transport and the Environment) and the city of Helsinki. The restoration work was mostly accomplished by volunteers in co-operation with the authorities. +
L
Love My River is a community led project developed by Groundwork CLM. Its main aims are tackling river pollution and creating a legacy that will protect the future of its waterways for years to come. It has so far carried out improvements at the River Chor and River Tawd in Lancashire. +
C
Lower bank to create soft margins, create pool and run features, install woody flow deflectors and import flint cobbles for white clawed crayfish +
N
Lugg SAC restoration via farm advise and farm interventions. Mitigating impacts of agriculture, riparian habitat creation, fish passage and reed bed creation +
R
L’effacement des plans d’eau n’a pu être envisagé.
Les travaux réalisés sont les suivants :
• réalisation d’un chenal de contournement sur
l’étang de Champeau. Le système, permettant le
partage des eaux en amont de l’étang, est réalisé
grâce à des palplanches métalliques découpées pour
respecter une répartition constante et pour absorber
les crues
• équipement des étangs de Fortier et de Cheteau
de moines hydrauliques
• changement de huit ouvrages de franchissements
de cours d’eau, pour restaurer la circulation piscicole
entre le Cousin et ses affluents. Les buses ont été
remplacées par des arches, des ponts en bois ou des
dalots carrés aménagés
• clôture de 7,6 km de cours d’eau pour limiter l’impact
du piétinement. +
E
L’ouvrage a été arasé à la pelle mécanique sur une
hauteur de 1 m et sur toute sa longueur. Trois miniseuils
noyés ont été mis en place sur 100 m en amont
du seuil afi n de maintenir l’équilibre du profi l en
long et éviter l’érosion régressive. C’est également
pour cette raison que la solution d’effacement total
de l’ouvrage n’a pas été retenue.
Des mesures complémentaires ont été mises en place
sur le site : des protections de berges en géotextile
ont été installées pour éviter la perte de surface – par
érosion des berges – des terrains attenants.
Enfin, des mesures ont été prises dans le but de diminuer
l’impact des travaux : réalisation d’une pêche de
sauvegarde et travail à sec avec mise en place d’un batardeau
pour dévier temporairement les écoulements. +
C
Manchester City Council identified that the Clayton Vale portion of the study area (east of Bank Bridge Road) was occupied by a historical landfill site, which was used for the disposal of ash cinders from the Stuart Street Power Station and as a municipal landfill. Consultants Atkins are in the process of undertaking ground investigations to determine leachate, groundwater and soil contamination including waste characterisation testing to determine the status of these materials and to allow an effective remediation strategy to be developed for the any river channel/corridor restoration works and to prevent the creation of new pollutant linkages or the exacerbation of existing ones, in upstream demonstration area.
It will be a huge achievement if we can restore this most heavily degraded section of waterbody, but the aspiration is to create a safe riverine environment for all, reconnect and integrate the river corridor back with the adjoining greenspace and public parks, and restore the river so that it is capable of supporting diverse aquatic fauna once more. +
E
Mandalselva is regulated for hydropower production since 1947 and this has impacted the conditions for Atlantic salmon in this river. The project "Miljødesign Mandalselva" used the concept of Environmental Design as described in the "Handbook for environmental design in regulated salmon river (Forseth and Harby 2013) and was accompanied by thorough research efforts in order to study which measures would be suitable to improve the conditions for salmon and at the same time to take into account hydropower production. This researcj was led by the Norwegian Institute for Nature Research (NINA) and conducted in cooperation with SINTEF Energy, Norce Research and Skandinavisk Naturovervåking. It included i.a. a trade-off analysis between the production of Atlantic salmon and the production of hydropower by examining the use of several physical mitigation measures and changes in release of water. Local stakeholders and public natural resource management were involved by means of a counceling group. As a result, nine weirs in the river were removed and further habitat improving measures were put in place (e.g. installation of gravel habitat). +
M
Manor Park was redesigned to tackle the Japanese knotweed on site, rather than dumping it in a hazardous landfill site hundreds of miles away. This invasive species can be a huge problem as it grows very quickly and crowds out all other plants and wildlife if left unmanaged.
Also at Manor Park, wetland areas and wildflower meadows have been created. The EA also updated and improved the play area. And it is now much easier for people to access the river itself.
The EA working with local groups such as the Quaggy Waterways Action Group (QWAG) resulted in ideas such as distributing waste logs from the sites to resident’s gardens. The logs act as a natural habitat for the stag beetle, a protected species. We worked closely with local police officers to design the park to be a safe, crime-free place. Local people can walk dogs, bring children, splash around in the river, or simply catch a glimpse of a kingfisher flitting about near the water. The restoration work takes account of the effects of climate change. For example, colourful Mediterranean plants in the ‘Sunshine gardens’ need less water than most indigenous species. They will be better able to cope with hotter, drier summers.
The channel of the river was improved to restore low flow features. +
B
Many fish species such as the salmon, sea trout and eel have to migrate hundreds of miles from the sea to the headwaters of rivers such as the Trent to spawn. Other coarse fish such as the barbel, chub, roach and perch do not migrate from the sea but they do need to be able to swim up and downstream to reach different parts of the river that will provide suitable habitat so that they can complete their lifecycle.
Weirs, such as this one, can prevent them from migrating to upstream and into the many tributaries of the Trent system. They create barriers that divide up a river into isolated sections. As a result, wildlife, water, silts and gravels are no longer able to move freely through the river corridor which in turn means that it no longer functions effectively as a healthy river ecosystem.
Burton Bridge weir falls within the ‘River Trent from Anker/Mease confluence to River Dove’ water body. It is classified as having poor ecological potential. This poor potential is due to diatoms being assessed as being at poor quality, with fish and invertebrates at moderate quality. By improving fish passage along the River Trent, we will help the river to move towards good ecological potential. +
R
Many watercourses within the River Rea Catchment are failing to meet the required standards under the Water Framework Directive (WFD) due to failing fish numbers. The River Rea has long been known as a catchment in serious decline as a result of sedimentation, poor agricultural practices and fish migration barriers. The Severn Rivers Trust walkover surveys of the River Rea, confirmed that suspended sediment load is seen to be impacting on the ecological health of the river and a major cause of fish failure. Impacts such as agricultural run-off from fields and bank erosion caused by farm animals are major contributors to an excessive quantity of sediment entering the river system. Also good riparian habitats are in decline due to over shading and over mature and diseased alders dying and falling into the river causing excessive blockages and bank erosion scars.
'''Planned outcommes
*Reduced agricultural run-off - reduced the in-stream sedimentation and fertiliser contamination, improved farming practices
*Improved biodiversity – improved in-stream habitats, re-established fish populations, improved invertebrate biodiversity, and control invasive species.
*Improved river water quality - reduced diffuse and point source pollution. Work towards achieving GES.
*Improved fish migration - removed un-necessary weirs, re-established spawning grounds.
*Reduced lateral river erosion and poaching - installed revetments, reduce poaching by reducing livestock access to watercourses.
*Improved flow regime – Reduced abstraction and or augmentation, plus wetland creation.
*Social - improved environment for recreation, promote interest and local community involvement in river restoration and healthy environment.
*Economic - improved fisheries, introduced farmers to the 'Passport Scheme', reduced farmer’s expenditure on fertilisers, pesticides, fuel and top soil replacement.
*Flood Defence – Create wetlands and wet woodlands and reduce sediment to mitigate flood risk. Raise flood risk awareness.
The River Rea restoration Project is a partnership project that will use CRF funds to improve watercourses in areas of the Rea Catchment that are affected by sedimentation, diffuse pollution, degraded habitat and obstructions to fish passage. The restoration project on the Rea will help to remediate these issues, by working with farmers to encourage the installation of cost-effective and environmentally friendly alternatives. These include coppicing of riparian habitats, designating buffer strips between the fields and rivers and fencing and re-establishing eroded banks. The Severn Rivers Trust aims to improve the habitat and connectivity in order to encourage a sustainable return to natural river processes and reduce diffuse pollution from farmland to ensure that the failing water bodies achieve Good Ecological Status under the WFD.
Through restoration work, the project will address issues
including:
* Sediment which has a direct adverse effect on water quality
* Barriers to fish migration, preventing fish from reaching habitat that they should be present in
* Interrupted natural downstream movement of substrate which reduces spawning habitat for salmonids
* Poor in-channel and riparian habitat for riverine species
Community engagement is essential to the long term success of the project as it encourages local ownership and support. It is seen as an integral part of an integrated catchment management approach.