Property:Lessons learnt
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This is a property of type Text
B
The value of a multi-benefit scheme, through joint funding and agreed outcomes.
The value of good PR and information from an early stage in project development. +
G
The wetland basin is quite large, sized for greater flows than have been experienced so far. This means that the water in the treatment basin overflows only during very heavy rainfall events. This is not a significant problem, it just means that the basin is acting more as an infiltration basin rather than a temporary storage basin. The system still functions to prevent polluted water entering the stream.
The plug planted sedges in the basin are thriving in this environment as the system was not fully activated until the plants were well established. However in the more shaded swales with greater velocity of flows and concentration of pollution the plugs have failed and need to be replanted.
Sedges have grown lush and verdant in the basin and water is cleaned and returned to the stream as expected or returned to the water table. Although perhaps not as aesthetically pleasing as in the design, the boulder arrangement at the head of the swales has worked well to slow water and prevent excessive erosion in the swales.
Water quality issues were far more significant than we had anticipated on commencement of the project, particularly in relation to domestic misconnections. High pollutant levels were evident beginning of our swales. We also found that although we proved our systems had a beneficial impact on water quality, just downstream of each project were outfalls which would bring in yet more pollutants. Therefore wetlands and SuDS alone could not demonstrate catchment level water improvements needed under WFD. Small scale interventions have a place in a suite of wider measures that need to be tackled with more drive, especially pollutant impacts from misconnections and vehicle use. +
L
The wide-ranging discussions held at the start of the project served to reconcile the different expectations and to allay the concerns of users. The solid technical feasibility study and the realistic impact assessment facilitated the acceptance of the project by all stakeholders and local residents. +
U
The work has resulted in rapid evolution of the site to a condition of improved physical heterogeneity (in-channel and wetland areas), with associated ecological responses. This has also resulted in a general aesthetic improvement, from a very simple canalised, embanked and perched channel to one that is much more physically variable, natural-looking and connected with standing water features (i.e. wetlands). The planting of trees in the riparian zone also benefits the site in this regard.
A practical benefit of the works was the improved protection of key areas of farming land from local flood risk. This was achieved through the removal of embankments on river right, permitting greater floodplain connectivity (with associated physical/ ecological benefits) to the east/ south of the channel while reducing pressure on the opposite bank. Furthermore, the implemented works greatly improved agricultural drainage; the bed of the restored channel was over 1 m lower than the previously perched condition, meaning that field drains could flow freely where they had previously been backed-up. Although not a primary objective of the project, considering these design objectives was essential to achieving buy-in by the local farmer.
There are also more general Natural Flood Management (NFM) benefits of the project. With greater floodplain/ wetland connectivity, there is greater inundation of areas adjacent to the channel under certain flood magnitudes. The storage of water in such areas will provide an increased level of protection to downstream areas. Furthermore, the re-establishment of native woodland will also contribute to NFM, adding roughness to the floodplain (slowing flows and increasing water storage times) and increasing the interception of water (surface flow and rainfall) through slowing flows and water absorption. Through such processes, the works will provide greater resilience to the effects of climate change. This is also the case for drought conditions; the previously homogenous condition of the channel has been replaced with a much more diverse morphology (particularly considering the wetland areas) that provides far greater potential for biotic refugia.
The work has generally improved the understanding of the benefits of such projects and the appropriate methods of their delivery. This has been a key case study for this type of work for SEPA and, with monitoring ongoing, dissemination of information will provide an invaluable resource to the wider river restoration community.
Given the explicit development of an integrated steering group and the associated project management approach, challenges during the project were minimised. Also, experience from previous construction projects by the design/ build team meant that many potential issues were avoided. There was careful planning of the construction phase of the project such that the most intrusive works (i.e. construction of the realigned channel and large wood implementation) were conducted ‘offline’, minimising the risk of high flow events impacting the works and fine sediment pollution. Such ‘assisted recovery’ designs explicitly require a degree of ‘field fitting’, allowing for unexpected issues encountered to be managed through appropriate short notice design variations. This was the case in the furthest downstream section of the site where, due to wet ground, it was not safe for construction machinery to excavate the initially proposed realigned channel in this area. It was therefore decided that the proposed design be modified such that the third (furthest downstream) wetland feature would be instated through this ~200 m long section, subsequently proving to be an appropriate revision. Such a short notice adjustment was only possible due to the close and established working relationship between the designer, regulator (i.e. SEPA) and contractor.
H
The work was carried out by a joint NRT/RGFA work party which enabled sharing of expertise between the two parties. +
K
There are no lessons learnt as yet.
We are keen to get insights from any similar projects targeting river flow restoration/support through perched reservoirs derived from upland mining operations. +
I
There are some significant limitations to Manning's equation, especially in waters that are heavily impounded as most Essex rivers are. This means that any attempts to use this equation to work out the flow and height of the water is limited, this adds a degree of complication to any water height and flow calculations. If this is the case, then water heights from specific days or contact with the local EA hydrologist is recommended to allow real time calculations to be taken at times of known flow. +
B
There is significant Archaeological interest on the site. With an identified Roman Villa remains in the local area. This adds a significant cost element to the project. Investigations are currently underway to identify the implications for this project but this may make the pond and wetland enhancement uneconomic. Early contact with the local Archaeological unit is recommended. +
H
These measurements show the potential of stimulating the origination of gravel beds. Actively introducing gravel would be a technological approach, which may be undesirable. If gravel is already naturally present in the stream, extra gravel may be added, but otherwise, a Building with Nature approach is considered more desirable.
Flow velocity variation can also be stimulated by main channel mowing or by introducing dead wood. When there is insufficient space for these natural measures, (as is the case for the Tongelreep), introducing gravel is an option. Providing sufficient shade over the gravel area is important. +
R
This has been a 3-year project. The partnership has taken that time to become established with clear objectives for the future. Partnerships of this size do take time. +
P
This has demonstrated that river restoration can be achieved by private developers as a cost-effective mitigation measure. The construction cost of the scheme, mostly earthworks, was approximately 5% of the total.
It is important to show that these types of schemes can be delivered effectively by private developers, in close consultation with other stakeholders. This complements other river restoration work being undertaken by the public sector.
Finally, in the process of facilitating development (which assists in economic regeneration) these types of restoration schemes can contribute a range of ecosystem services including supporting services (habitat creation; biodiversity); regulating services (flood control) and cultural services (potential recreation and amenity through riverside walkway; tranquillity; and educational services through being used as a demonstration project). +
R
This is a constant battle, it is something that needs to be undertaken each year. There was no action in 2008 and this saw a huge increase in the presence of pennywort. As the occurrence of the plant becomes less the time and cost associated with the project also decreases. +
P
This is a small project, total cost is expected to be less than 5k. However, it still has to be treated as if it is a major project. This has led to a very bottom heavy project with a substantially more spent on the consenting process rather than the delivering the project. There is a strong argument to suggest that any river restoration project must be worth the consenting process and smaller projects may not offer value for money. +
W
This is an ongoing project still in its early stages. +
S
This is the start of a 6-year programme of flood risk management works within Leicester. The Soar is navigable in Leicester and as most work was undertaken to improve conveyance we were limited in what improvements to marginal habitat could be undertaken. Most work involved wetland creation within the river corridor and creation of backwaters. Going forward future flood schemes on the Soar tributaries should look at the in-channel and marginal habitat improvements which should help to have a greater impact on WFD classifications.
Leicester is home to surprising amount of protected species for an urban environment. A lot of monitoring work was undertaken and careful consideration given to this during construction. This is something that will feed into future work to ensure that new foraging habitat created is not affected by subsequent work.
Leicester has a very diverse community which speak a large number of languages and for many English isn't their first language. A lot of the information we are trying to convey is in English which means that especially in tackling issues around diffuse pollution the message may be lost. We are looking at ways we can be more effective in getting the message out by doing work with schools and community groups who can then pass the message on. +
F
This permeabilization
represent an
improvement in the
longitudinal
connectivity of this
river reach, however
it is considered
necessary to
permeabilize the weir
located 3 km
downstream in order
to achieve a more
complete
reconnection. +
U
This project did pose some issues during its delivery. The extent of the berm creation and bed reprofiling was limited due to the presence of overhead power lines. A safe working method was implemented by the Ops Delivery team. Initially the excavator to be used had an 8m reach; this was also used on the North Channel job. However this reach was wider and to maximise the benefits of the project a long reach had to be brought to site. This came at additional cost but enabled effective delivery of the project. The long reach machine was also used on a few parts of the North Channel project which were out of reach form the original machine. The tree works described above were also able to be carried out with the larger machine. +
This project did pose some issues during its delivery. The generally narrow nature made any changes made to the bed more sensitive than in other reaches of the Frome. The existence of gravels within the river bed was not as extensive as first thought. There were sections that were mostly clays which made it harder to reprofile effectively. The decision made on site was to minimise or exclude any works to the bed if gravel quantities were low.
The banks of the channel were high and steep; they were also quite soft so when trenches were dug to install LWD structures the banks in places seemed quite fragile. This limited the angle which could be dug and did restrict the use of this technique in places on the reach.
The benefit of adding value as described above cannot be under estimated. As described it can give a project additional materials (tree limbs etc) but can also gain acceptance of the project by other stakeholders such as the tenant farmer or river keeper. These can be achieved with minimal additional cost to the project. +
R
This project had a range of key challenges that were overcome through the design process, including:
• The restoration of natural hydromorphological processes whilst minimising the potential for large scale channel migration. This was resolved through the design of a multi-stage channel which allows the low flow channel to adjust within a more permanent high flow bank line. Seeded gravels were also allowed to rework naturally to create a wide range of in-channel habitat niches. The two stage channel safely accommodates both the low dry weather flows and the high flood flows.
• Ensuring that the river could be re-meandered through contaminated land at the site without increasing remobilisation of in situ contaminated sediments and leachate. An uncontaminated capping layer using uncontaminated soils was used to protect the environment and park users from contaminated materials.
• Minimising the need for expensive off-site disposal of contaminated materials and the need to import uncontaminated soils for capping. Soils on the site were categorized as contaminated and less contaminated (i.e. with contaminant concentrations below hazardous levels), and the former were used as a base layer for landscape features within the park. These were capped with less contaminated soils from the site to prevent exposure to the wider environment. +
W
This project has benefited from detailed investigative work and consultations that were undertaken as part of the site selection, scheme design and impact assessment work as well as for the preparation of the monitoring programmes. However, the need to find such a large site that met all the requirements was a long-term and costly exercise. There has been a full time project manager with supporting teams including representatives from statutory and non-statutory authorities and these aspects have enabled problems to be foreseen and rapidly addressed. The team approach has also allowed innovative new design elements to be identified which should provide high value at low cost (e.g. the island features in the site and a new ‘heterogenic’ borrow-dyke design).
The initial monitoring is still ongoing, and the full results from the first five-year monitoring programme have not been reported yet. However, from the interim progress reports that have been produced by ABPmer and Jacobs up to the end of 2010 (i.e. up to four years after the breaching), the following general observations have been made:
Breaches and channels: The breaches and channels through them are very stable which confirms the effectiveness of the approaches that were taken to design them.
Accretion: Within the site, sediment accretion has occurred relatively consistently and evenly due to the slow flows and stable internal creek/channel configurations. In the first year after breaching (2006 to 2007), accretion was around 10cm (of which about 50% is considered internally relocated materials and 50% externally imported sediments). In each subsequent year, the annual accretion is considered to be predominantly related to imported sediments and amounted to 3 to 5cm on average (specifically 5cm in both 2008 and 2009, and 3cm in 2010).
Invertebrates: The accretion and the relatively stable and depositional nature of the environment has helped to promote rapid benthic invertebrate colonisation of the mudflat (approx 80ha in extent). After the first, year invertebrates abundance was at 20,000 organisms/m2 and has ranged between 10,000 and 20,000 organisms/m2 in each successive year. The benthic assemblages have been dominated by large numbers of mud snail (Hydrobia ulvae) and although the patterns of organism recruitment are clearly complex and variable, there is evidence that the assemblages are maturing over time. This is indicated by the bivalve species becoming an increasingly important component over time (representing 2%, 4%, 14% and 26% of the populations in each successive year).
Birds: The bird monitoring (by CJT Ecology) shows that over the course of the four completed years of the monitoring programme the site has been supporting very good numbers of waterbirds. This was the case even from the first winter survey (2006/07) when the site supported around 7,000 waterbirds and included good numbers (i.e relatively high in a national or international context) of many key species such as shelduck, dunlin, black-tailed godwit, ringed plover and golden plover. In the following two winters the value of the site continued to improve as the abundance of waterbirds increased to around 10,000 and then 12,000. For the most recent winter (2009/10) however the overall abundance levels declined slightly. These broad trends are strongly influenced by some major inter-annual changes in the abundance of certain species which, in turn, are likely to be influenced by the weather conditions (e.g. particularly bad weather conditions were experienced in 2009/10 when compared with other years) and/or a range of other factors that influence the natural dynamics of bird populations (e.g. breeding success, timing of migrations, national population trends and inter-annual or inter-generational changes in roosting/feeding site selection). It is of note however, that the numbers of birds using the site as a roost reduced in 2009/10 while the number of birds feeding increased. This may indicate that the habitat and the relationship with migratory birds is still maturing and developing or that under adverse weather
conditions the site’s value as a feeding site as opposed to a roosting site increases.
Saltmarsh: Saltmarsh coverage of elevated areas of the sites (approx 25ha in extent) has occurred relatively rapidly. On average plant coverage (i.e the amount of marsh plant compared to bare mud at any given location) has rapidly increased from less than 1% in 2007 to 6% in 2008, 60% in 2009 and finally at or around 100% in 2010.