Property:Lessons learnt
Jump to navigation
Jump to search
This is a property of type Text
R
The importance of gravel and floodplain connectivity to drive significant change. Need for wood in by-pass channel. Where the constraints have been addressed by realigning and re-naturalising the channel at Grange Farm, habitat improvement has been more successful, although further intervention is required. Introduced gravel has been displaced in high flows and needs to be replaced with larger calibre material which will remain stable and restore the designed pool-riffle sequence. The abrupt change in valley floor gradient at this site constrained the design of the new channel and caused this situation; this is unusual and should not be a deterrent to similar river restoration schemes elsewhere. +
The in-channel works have been successful and flow diversity and sinuosity has been achieved. Both the berms and woody debris have vegetated rapidly and the works are now barely discernible. A diverse range of marginal vegetation has established and trout were observed resting on the glides. Ecological surveys were carried out in August 2013 and the results of these will determine the extent of ecological recovery following the works.
Some adaptive management of the plug has been necessary as a result of the extremely high flows experienced immediately after construction. Clay, overlain with coir matting, was used to reinforce the plug and this appears to have worked well with flows directed around the meander other than in high flows. Some erosion has occurred on the outside of the meander bend cutting back the bank and exposing patches of bare chalk. The material eroded has been deposited downstream of the meander loop and formed a natural berm on the inside of the bend. On the day that RRC visited the Environment Agency Field Team were on site pinning an alder tree that had fallen across the meander loop. The Alder was repositioned in order to maintain access for canoeists as well as retain its function as large woody debris.
The floodplain reconnection has been successful with suspended sediment settling out on the floodplain during high flow events and water draining back into the river as flood levels subside. +
G
The in-channel works have been successful and flow diversity and sinuosity has been achieved. The lateral berms and woody debris have vegetated quickly, providing physical habitat and creating additional flow diversity. Marginal vegetation is well established and the banks support an extremely diverse range of species. The planted trees are growing well and several self-seeded trees, predominantly alder, are establishing along the banks.
The new backwaters hold an abundance of fish fry, and trout were observed resting in the pools. In addition, a kingfisher and otter spraint and prints were sighted during the RRC visit. Ecological surveys were carried out in August 2013 and the results of these will determine the extent of ecological recovery following the works. Some adaptive management of the upstream end of the plug has been undertaken. Locally sourced turfs have been used to reinforce the plug and reduce erosion during high flows. Some cattle poaching has occurred at the upstream end of the reinstated channel, and although action is not currently necessary, this will continue to be monitored by the Environment Agency. +
A
The key findings at Alkborough are:
# Sediment accretion within the realignment site is continuing but at a slower rate than was initially recorded in 2007/8. Much of the site is now at an elevation of 3.1 m or more. Accretion levels on the mudflat outside the site can be considered stable with the exception of the infilling of a particularly low lying section of the mudflat where significant accretion has taken place.
# The sediments both inside and outside the realignment site are described as fine-coarse silts, with fine sands being present in some areas, and are typical of the area. No changes in particle size were noted over time although water content and sediment organic content decreased inside the site between 2007 and 2008.
# The benthic communities are impoverished (low diversity, abundance and biomass) and reflect the low salinity and high turbidity of this part of the estuary. Outside the site, the infaunal species and their abundances are typical for this area with Heterochaeta costata and Paranais litoralis being the dominant species. Inside the realignment site, the community is dominated by invertebrate species typically associated with freshwater and terrestrial environments. However, infaunal estuarine species (predominantly P. litoralis) are present and widespread throughout the site.
# High tidal elevation and reduced flooding frequency appear to favour colonisation by vegetation. Whilst a significant amount of perennial rye grass (Lolium perenne) still exists, a total of 6 salt tolerant species were found including Phragmites australis, Aster tripolium, Atriplex prostrata, Ranunculus sceleratus, Puccinellia maritima and Rumex obtusifolius. Of these species, P. australis was the most common and widely distributed and was generally found along the edges of old agricultural drains.
# The conditions within the site have led to the development of a mosaic of generally sheltered habitats, not present on the established mudflats outside the site, which have attracted a variety of bird, fish and epifaunal invertebrate species. Many of the fish species present are typically associated with freshwater and were not found in samples outside the site although a number of euryhaline fish were also found. Commonly occurring species included flounder and eel and the size distribution of flounder suggests that the site is acting as a nursery for this species. This is a valuable function of the site considering the historic habitat loss elsewhere in the estuary. The high densities of Neomysis integer caught suggest that this species is an important food source rather than the benthic invertebrates which are not thought to be present at sufficient densities to support the number of birds using the site.
# Of the birds present, 16 species of waders use the site for feeding, 5 of which also use the site for roosting. Of these, lapwing, curlew, redshank and dunlin were the most frequently recorded. 18 species of wildfowl used the site for feeding, with 13 also roosting. Shelduck, teal, wigeon and heron were the most frequently occurring species. Particularly high numbers of golden plover were noted during November 2008. A number of the species using the site are of conservation significance and classed as Annex 1 species under the Habitats Directive. There is a broad association between bird distribution and habitat type with golden plover and curlew generally feeding in the infrequently flooded grassy areas, away from most other species. However, the majority of bird activity is in one sector which contains a wide variety of habitats. It is therefore difficult to draw conclusions about habitat preferences or use for individual species.
# The Alkborough site has the dual aim of flood defence and compensation for habitat loss due to coastal squeeze. That is, replacement of mudflat habitat. Given the site design, the elevation and the restricted flooding, it is unlikely that this will be achieved in the long term and there is already evidence that the site will become vegetated. However, the site does appear to be acting as a nursery area for fish and is a significant feeding and roosting area for birds. In this respect, the development of the site appears to have been beneficial to this region of the estuary which is otherwise largely characterised by narrow mudflats with species poor communities and, in most areas, little vegetation.
U
The key issue regarding this project only became apparent after its completion. Comments received from the Dorchester Fishing Club described concern over the installation of the woody material. The concerns were related to the size of the wood in the channel and how it could come loose during high flows. The Project Manger has since described how the limbs were buried in trenches within the bank which wouldn’t have been visible post works. This technique should ensure no movement during high flows. The comment regarding the size of wood in the channel is probably valid. As a result of burying the larger end of the limb on the bank it in some cases only left thinner branches in the water. In hindsight larger limbs should have been sourced in some locations to ensure the part of the limb in the water was as large as possible. If over the winter some of the wood isn’t having the desired affect there is an option to source several larger limbs and fix those at key points next year. +
M
The key learning points:
• Good planning required to fully understand a large site, ensure surveys are specific from an early stage, understand the difficult areas in detail
• Good communications internally and externally are essential, consider using a RACI tracker for large project teams
• Involve archaeology fieldworks as early as possible to understand risk and investigation techniques such as GPR and intrusive works.
We have worked with voluntary groups and Universities, to involve students in long-term monitoring of the habitat and species establishment. Brighton University currently have masters and PhD students undertaking research that includes Medmerry. There is also the potential to include Medmerry in core environmental and wetland modules.
Lessons from translocating water voles, have been published in 'In Practice' to ensure good practice is circulated amongst professionals. This includes specifications of water vole exclusion fencing; for example, the mesh size formerly recommended in the water vole conservation handbook proved to be too large, allowing juvenile water voles to pass through. A full lessons learnt exercise and an CIWEM site visit are planned for the summer of 2014.
As expected the shingle beach, which used to be the flood defence, has rolled backwards and has been flattened by the sea. This does not impact the flood risk because the inter-tidal area that the scheme has created acts to absorb and dissipate the sea's energy. +
O
The lateral dike which is part of the side channel system helps to guide water flow in the main channel in such a way that navigation is positively affected. Though this dike was build prior to the side channel project, it does serve as an example of a potential restoration technique which benefits both natural dynamics and ecology as well as navigation along the main channel. +
S
The levels should have been set so that no lowflow runs through the culvert surrounding the park. However, some flow does still go through the culvert. This means that the channel within the park can suffer from very low flows. +
R
The long term overall benefits in terms of biodiversity of the restoration will been significant. However during the planning and the delivery stages several issues came to light that made the work more complicated and increased costs. +
T
The main flagship site at Madebrook involved the design, planning and construction of a new de-culverted watercourse in an urban setting. The technical challenges were many and steadily overcome by the project team. Costs were high and this made budgeting a challenge, good collaboration and flexible design allowed the project to proceed to a successful conclusion. Involving the local community at an early stage and keeping them involved is key in a project which will at times disrupt the local area. Good liaison has helped maintain good will and has helped build confidence as we move on to new projects in the local area. +
E
The main overall effects on river geomorphology determined by
Tena et al. (2013, 2014) highlight the remarkable but irregular
effectiveness of flushing flows for macrophyte removal, which reaches
95% in the sub-reaches closer to the dam but decreases substantially
downstream. The released flood showed a significant ability to entrain
and transport sediment, but limited overall geomorphic impact. Mobilization
was primarily limited to fine-medium gravels, whereas bedload
rates remained low, likely due to the short duration of the events. The
seasonality of the releases was directly related to sediment availability,
with higher sediment peaks observed in autumn despite similar flushing
peaks. In parallel, different routing velocities were found for discharge
and sediments.
Some of these findings can be attributed to the fact that the rate of
discharge increase per unit time during flushing flows is an order of
magnitude higher than during natural events (Batalla and Vericat,
2009). Therefore, flushing flows show greater transport capacity than
the natural floods, despite having a lower magnitude and shorter
duration. The authors also concluded that the Lower Ebro River shows
evidence of being under geomorphic adjustment 40 years after dam
construction.
Most importantly, flushing flows in the Lower Ebro River have been
shown to be compatible with hydropower operation. Gómez et al.
(2014) calculated and compared the cost of the reduced power
generation due to the release of flushing floods with the observed
willingness to pay for river restoration programmes. They concluded
that the provision of artificial floods had a cost equivalent to a small
fraction of the energy delivered to the market and overall annual
revenue (0.17% for the two annual flushing floods). +
B
The management through landstewardship agreements and a participatory (universities, volunteering, citizen science), approach have facilitated the integrated management of the wetland and awareness raising. Socio economic improvement of local business (i.e. navigation) has been launched through collaboration with navigators for public use purposes. +
R
The measures ensure water-covered areas when the power plant is “hydro peaking”, and the combination of the thalweg enhancement and the placing of groups of boulders, contributes to a large part of the river basin having water velocities within the salmonid's preferences. "Sjøforsløpet" has the potential to add significant areas of good salmonid spawning and breeding areas to Rossåga, but time is needed to judge the success of the measures. According to the water management regulations, the ecological potential for fish has changed from poor to good. +
The measures in the Børselva watercourse (Børselvvassdraget) have created better water quality and hydrological continuity (open water flow) in the formerly overgrown watercourse. The flow levels have improved, self-cleaning has improved and pollution has been reduced. This has resulted in a more varied benthic fauna, better spawning and growing conditions for the trout and improved conditions for the bird fauna. +
The need to precisely control the management (hydraulic management and grazing):
- breeders do not strictly respect the demands of the managers (grazing period and grazing pressure)
- capcity of the pumping staition inferior to that announced by the manufacturer
The need to organize from the beginning:
- the monitoring at mid and long terms
- the means to ensure adaptive management in order to respond to the possible gap between the vegetation obtained and those predicted.
- The need to raise awareness (breeders, hunters) that a more environmentally friendly environment offers more irregular services than a area only managed for a particular service +
S
The overall conclusions are that without water quality data, it is not certain how big an impact on water quality unsewered properties are having. On the face of it, septic tanks do not present as big an issue for river ecology as soil erosion and sediment transport and that a whole catchment approach to understanding the pressures is needed. +
N
The park users, particularly dog walkers, now see the open Ravensbourne as a focal point, circling the area and making use of the crossing points. Children and dogs play along the banks even though the site has still to mature.
The marginal planting is suffering disturbance from dogs and children and may take longer than expected to establish a good cover, though this may eventually produce a good diversity of edge habitats. The wildflower plugs have been decimated by crows in search of worms. About a third were removed from the ground and became desiccated.
The planting scheme was designed as a balance between creating an instance impact for the local users and allowing natural processes of colonisation to occur. Even so the local users have stated that they would have expected more immediate impact from the planting.
The success of the project can be attributed to the multi-disciplinary project team and the Partnership between the Borough Council and the Environment Agency. +
A
The positive outcome of the river restoration project in Aston Clinton is as a result of great partnership working across all the stakeholders involved. This project really demonstrates that by pooling skills and resources across many organisations and individuals, costs can be reduced and all stakeholders become passionate about achieving an end result that reflects everyone's interests; flood management, biodiversity, ecology, farming and benefitting the community.
Though the project did not run smoothly all the time, this meant that lessons have been learnt regarding project management, especially CDM regulations, early engagement and communication. which can be implemented into future projects and future partnership work. +
R
The preparatory work for these weir removals involved:
- “Weir removal/modification Feasibility Appraisal” by JBA Consulting, covering hydrology, ecology, structure, services, contamination, cultural heritage and concept design.
- Planning Permission application (16/0459).
- Impoundment Licence application (NW/076/0006/005).
- Environmental Permit application (EPR/RB3396JX).
- Consultation and formal agreement with weir owners.
- Consultation with local community groups, interest groups and Councillors.
- Consultation with Local Authorities and other relevant statury agencies.
- Appropriate survey and mitigation for otters, bats, trees, crayfish, fish and invasive species.
- Design & tender of ground works.
- Health & Safety requirements.
- Construction Design & Management Regulations.
- Pollution control measures.
- Archaeological Watching Brief.
- Monitoring.
- Publicity. +
The preparatory work for these weir removals involved:
*“Weir removal/modification Feasibility Appraisal” by JBA Consulting, covering hydrology, ecology, structure, services, contamination, cultural heritage and concept design.
*Planning Permission application (16/0459).
*Impoundment Licence application (NW/076/0006/005).
*Environmental Permit application (EPR/RB3396JX).
*Consultation and formal agreement with weir owners.
*Consultation with local community groups, interest groups and Councillors.
*Consultation with Local Authorities and other relevant statutory agencies.
*Appropriate survey and mitigation for otters, bats, trees, crayfish, fish and invasive species.
*Design & tender of ground works.
*Health & Safety requirements.
*Construction Design & Management Regulations.
*Pollution control measures.
*Archaeological Watching Brief.
*Monitoring.
*Publicity. +