Property:Monitoring surveys and results
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Restoring the river continuity of the Bresle River by returning it to its original bed in Sénarpont +
Biological monitoring of this project is based on fish
populations. The pre-works situation was assessed in
2013 on the basis of an electrofishing campaign in
the leat. The assessment was carried out with redd
countst on the project site in 2013 and 2014, and in
2015 with a count in the upstream 8 kilometres of
river made accessible for fish by the works (the count
was carried out in a partnership with the Onema
salmonid centre). Post-works monitoring was done
from 2013 to 2015. Two inventories were carried out
in 2015 by the Seinormigr association, using the IAT
(trout abundance index) protocol. The initial and
post-works assessments did not implement identical
methods, i.e. the first was a fish rescue in the former
leat and the second implemented the IAT protocol.
The results are nonetheless useful on the basis of
individual density calculations.
The bypass of the Sénarpont hydraulic structure
made possible to restore the continuity of the Bresle
River a further eight kilometres upstream. The works
also improved the functioning of the alder and ash
wet woodland by enhancing the supply of water.
The operation also restored 650 metres of river by
reducing the impounded reach to 400 metres and
reinjecting water into a number of side channels
(250 metres). The connection between the riverbed
and the side channels in the project sector created
new expansion zones (in non-critical areas) for flooding.
These lateral connections improve water quality
through enhanced self-cleansing and the creation of
greater habitat diversity, a positive factor for biodiversity.
The former impounded reach was replaced by a
series of diversified flows in multiple channels in the
valley bottom. Fine sediment was removed to reveal
the coarse substrate that is now renewed naturally
thanks to the restoration of the morphodynamic
process.
Monitoring of fish revealed that prior to the works
in 2013, trout density was 0.5 fish per 100 m². In July
2015, after the works, the measured density was
5.6 trout per 100 m². The trout population gained
in numbers by a factor of 11 with a significant increase
in the percentage of the juvenile population
(30% of the total in 2013, 85% in 2015). The site has
thus become highly favourable for spawners and the
growth of juveniles.
At the end of 2013, just after the diversion of the
river to its original bed, several sea trout were observed
spawning in the restored channel. Five redds
for migratory salmonids were observed on the site.
One year later, a dozen redds were noted. During
the inventory, bullheads and eels were also caught.
The strong point of this project is the restoration of
the overall functioning of the river and of its side
channels for a relatively small amount of money. The
Bresle EPTB succeeded in defending its restoration
objective and in negotiating over a long period to
convince all the land owners and the town council.
Today, the results are positive. Local residents have
easier access to the nature and take pleasure in observing
a dynamic river with a diversified ecology.
This project was all the more beneficial that a number
of mill owners who were previously hesitant to
work on their installations are now ready to launch
operations to restore river continuity.
Biological surveys were conducted before works via a
fish inventory and invertebrates monitoring conducted
downstream and upstream of the currently restored
area. Monitoring measures after completed work were
implemented. These were taken in 2011 and 2012 and
covered the physical aspects - flow types, substrate, etc.
- on riparian vegetation, as well as the biological aspects
- benthic macro-fauna, fish population, insect fauna,
amphibians, birds and mammals. All these surveys are to
be compiled and included in a map database (GIS). The
monitoring will be conducted annually over a five-year
period (until 2016).
This operation decompartmentalises the Fontenelle
over 1.2 km and reopens access to the Rançon and the
Seine to biological communities between the confluence
and the next upstream weir on the Fontenelle.
Electrofishing analyses in 2011 show a recolonisation of
the area by brown trout. Functional spawning grounds
have also been observed in the rehabilitated site (observation
of brown trout reproduction in 2012). The
removal of the structure allowed recolonisation of eels
across the whole restored stretch. Upstream of the site,
eel density rose from 10.25 individuals / 100 m² in 2005
to 127 individuals / 100 m² in 2011.
Three months after the works, spontaneous aquatic
vegetation appeared; callitriche plants, marshwort and
common reeds have thus been observed.
Benthic invertebrates quickly recolonised the site.
Downstream in particular, groups characteristic of the
presence of organic matter - dominance of Gammaridae,
Diptera Chironomidae and Ephemeroptera - have
been observed, partly due to the significant and rapid
development of the herbaceous layer. Analyses in 2011
revealed the presence of Glossosomatidae caddisflies -
a group very sensitive to pollution - upstream of the
rehabilitated site.
The resumption of river dynamics with the appearance
of preferential areas of deposits and erosion is visually
apparent in the new bed. Compared to the initial situation,
flow types are more diverse, particularly on the
upstream part of the sector. The downstream sector
meanwhile flows through a distribution of rather lentic
water flows, owing to its slope, which are ten times
lower than upstream.
The risk of flooding is reduced by the presence of flood
storage areas covering several hectares along the new
course of the Fontenelle. The 10-year flood of 16 December
2011 provided the opportunity to observe this.
Two years after the works, a significant improvement
of the biological and morphological environment is observed,
with the rapid reestablishment of species and
the remobilisation of sediments. However, it is difficult
to have real perspective for the time being. The next
post-restoration monitoring will confirm or refute this
trend.
The success of this project depends in part on the major
coordination project set up by SMBVCS. Local residents
were involved very early in the project. The declaration
of public utility initially taken was not used, as all local
residents gave their approval.
With this renovation of the Fontenelle, half of its
course has regained its former bed. The river remains
perched over the whole 400 m stretch. However, the
restitution of the whole stretch into its original river
bed does not seem effective in terms of the cost-benefit
ratio achieved. The works would only concern a limited
potential surface of the spawning grounds and require
the end of fish-farming present on this site, which is of
local economic interest.
M
Brown trout have already been observed spawning on the new limestone gravels. Crayfish monitoring was carried out pre works and showed a very low baseline population with only 6 individuals caught, repeat monitoring of this will be carried out along with repeat bird surveys of the site. +
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By Intercepting run-off and trapping sediment, this scheme will help achieve better water quality preventing the loss of soil, chemicals, nutrients, and faecal organisms. A further benefit is their ability to temporarily capture water and slow down flow. his can reduce localised flooding. Improved back channel habitat that is better connected to the main river will benefit fish invertebrates and plants both in the riparian zone and amin river. +
S
By May 2013, over 1200 eels had passed through this pass.
Post Project Appraisal +
By intercepting run off and trapping sediment, all these schemes will help achieve better water quality by preventing the loss of soil, chemicals, nutrients, and faecal organisms. A further benefit is their ability to temporarily capture water and slow down flow. This can reduce localised flooding.
66 Landowners were engaged through a workshop and series of presentations to identify suitable sites, raising the profile of the effectiveness of rural SuDs schemes. 6 schemes were then taken forward and simple measures installed to reduce run-off. Some of the schemes were completed under a regulatory position statement related to the disposal of waste sediment from distilling. This ensured that regulation was proportionate to the risk, reflecting the small scale of the scheme and the overall environmental benefit. +
V
Cessation of vegetation removal led to an extended vegetation cover in the first year after implementation of the measure. Submerged vegetation and floating vegetation expanded more than riparian vegetation. +
R
Cette opération innovante sur le territoire fait l’objet
d’un suivi complet (physico-chimie, poissons, macrofaune
benthique, hydromorphologie) pour mettre en
valeur les bénéfices écologiques et servir d’exemple à
d’autres gestionnaires.
Une station de suivi est définie sur la future zone de
travaux, au niveau du pont présent entre les deux
secteurs à restaurer. L’état initial est réalisé en 2011 et le suivi post-travaux
en 2012 et en 2014. Les suivis hydromorphologiques
et hydrobiologiques seront reconduits en 2016.
L’action a des impacts positifs sur le cours d’eau qui
retrouve des écoulements diversifiés et des substrats
à granulométrie variée. Sur le secteur amont, le resserrement
du lit par la mise en place de banquettes
favorise une diversité des écoulements empêchant
ainsi le colmatage du substrat par les matières fines.
L’amélioration de l’hydromorphologie se traduit par
des vitesses, un faciès d’écoulement (radier, plat courant,
fosse) et une oxygénation proches de l’état naturel
pour ce type de cours d’eau. Ces observations
sont plus nuancées sur la partie aval, la réduction de
section étant légèrement insuffisante; du colmatage
en période de basses eaux est observé.
La survenue de crues morphogènes permettra de
suivre la capacité du cours d’eau à faire évoluer son
profil et à remobiliser les matériaux rechargés. Ces
améliorations offrent une diversité d’habitat favorable
aux espèces aquatiques comme le montrent
les résultats du suivi biologique. Cette plus grande
diversité d’habitats se traduit par une amélioration
des peuplements piscicoles (échantillonnages 2012 et
2014), avec une diminution de la densité d’espèces
de chevesne, gardon et goujon et une augmentation
et stabilisation du nombre de chabots inféodés à ce
type de cours d’eau.
La faune macro-invertébrée benthique réagit positivement
avec une diversité taxonomique plus grande
(30 taxons en 2011 contre 39 en 2012) et la colonisation
du milieu par une nouvelle famille polluosensible
(Goeridae, trichoptères).
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Community Involvement - Engagement activities will include public consultations, practical volunteering activities like beach cleans, and tree planting, and awareness-raising through media and face-to-face contact. +
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Counting of sea trout travelling upstream at Breuilen-Auge
has been carried out since 2001. This
monitoring is implemented under an agreement
with the owner of the dam and of the fishway.
Reproduction areas accessible to sea trout have increased
sharply, thanks to improvements works
carried out over the past 30 years. The proportion
of accessible surfaces thus increased from 15% before
1982 to 86% in 2009. The sea trout travelling
upstream monitored at the Breuil-en-Auge fishway
represented 2,500 fish in 2001 and more than 6,000
in 2008, a figure confirmed in 2009 with over 5,500
sea trout. As the monitoring station was located
upstream to many tributaries, the current Touques
stock is therefore now 10,000 sea trout, making it
not only the number one river in France for sea trout
but also one of the best in all of Europe. These very
good results are accompanied by a significant rise in
fishing tourism.
The scale of these actions and their results make the
Touques basin a benchmark for continuity in the
Seine-Normandie basin.
The Touques axis is completely open to migration,
but there are still a dozen or so more obstacles upstream
of the tributaries. There are several projects
under way. The most penalizing obstacle lies in the
middle part of the Calonne. This obstacle, devoid of
fish passes despite the regulatory obligations, neutralises
the efforts already made upstream in the
Eure département due both to the obstruction of
upstream fish migration but also damage caused by
the turbine on fish returning to the sea. +
O
Due to maintenance problems, the block structure had to be adapted. It will therefore take longer for monitoring results to come in. +
R
Due to the problems of sediment contamination stored upstream of the dam, a study
was carried out prior to the removal in order to make a diagnosis of the sediments and
their treatment. A plan is implemented to remove some of these sediments and place
them in higher areas where they were confined and stabilized by planting native
vegetation.
Two years after the removal of the dam, a monitoring plan was conducted to measure:
- Physicochemical parameters of water as temperature, dissolved oxygen,
conductivity and pH.
- Habitat availability.
- Quality of the riparian forest.
- Flora (macrophytes) and fauna (macroinvertebrates and fish) present in the
river, as well as exotic species.
The fish community in the Cofio River near the Robledo dam is: Rainbow trout
(Oncorhynchus mykiss), Iberian barbel (Luciobarbus bocagei), chub (Squalius
pyrenaicus), calandino (Squalius alburnoides) and Iberian gudgeon (Gobio lozanoi),
being Squalius alburnoides the dominant specie. All are native species of the Tajo River
Basin except from the rainbow trout that is exotic and comes from sport fishing.
Sampling points were determined both upstream and downstream from where the
dam was located. The main results of this monitoring show clear signs of recovery in
the river reach affected by the presence of the dam, with some differences between
the areas that were located upstream and downstream of the dam. +
E
Durham University undertook Archaeological Monitoring in 2017 and during the removal in 2018
Immediately post-removal WCRT have been conducting regular fixed-point photography across the site, to highlight how the river adapts and responds to being re-naturalised.
Drone-captured aerial imagery has also been recorded post-removal; once collated this can be contrasted with the footage captured pre-removal for before-and-after analysis +
R
E-CO have continuos data from detailed monitoring reaching back to 1988 on fish population (salmon and sea trout). We also have data on the invertebrate community in the river from before the hydro-power development started. There are also physio-chemical data, and continous data on discharge and water temperature. There are also data on the efficiency of the fishway, both for fish migrating up and downstream.
The data will be published in a small summary report at a later stage. +
S
Each month seven water samples are collected by the RSPB on the Leighton Reedbed and six at Hawes Water.
Each quarter this is extended to include three on Barrow Scout and two on Silverdale Moss (18 in total).
Samples are sent off for analysis. +
D
Ecological surveys completed before (2014) and after (2015 & 2016)the restoration works have shown that that invertebrate diversity has increased since the improvement works and the trout population has nearly doubled on the improved section of the beck. Engagement and involvement of the landowner has ensured that the improvements will be protected during any future maintenance works. +
A
Ecologists in the Environment Team at Buckinghamshire County Council carried out an initial assessment once the project was complete to establish what life was found in the newly created watercourse. They plan to carry this out annually to see how the river develops and establishes over time. +
M
Eel pass installed using a design that incorporating an eel trap for monitoring purposes - pass is already being used. +
S
Electric Fishing surveys to be carried out in the first summer following completion. +
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Electrofishing and invertebrate sampling, ditch blocking and water level monitoring, wet weather surveys +