Property:Lessons learnt
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4200m3 of earth was removed from the floodplain during the lowering and removal of embankments. Reconnecting the floodplain has created 19,500m3 of space for water which now reconnects to the lower floodplain frequently after intense rainfall events at a 1 in 2 event magnitude. +
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==Expectations and Response==
It was expected that the measures would have a positive effect on the river ecology, especially on bullhead, brook lamprey and salmonids due to the introduced hard bed substrates. A greater heterogeneity in substrates was expected which would result in re-establishment of Ranunculus and other macrophyte species. The increased hydrological continuity with the floodplain and exclusion of cattle benefits the riparian zone and typical riparian species.
''Ecological Response''
A total of 58 macrophyte taxa were recorded during the assessment of 5 transects. No invasive species were found and only one negative indicator Fennel pondweed was found. The key species brook water-crowfoot and hemlock water dropwort were only minimally present with less than 5% coverage. The most dominant species were Reed sweet grass and branched bur-reed with both species taking 10% of the coverage.
Compared to the pre-restoration state, the reach has less brook water-crowfoot and a strong increase in the negative indicator Fennel pondweed. A fewer number of taxa were observed and a reduced number of species were recorded as covering more than 5% of the channel. It was concluded that temporary disturbance caused by the construction of the measures could be the cause of this decrease. The installation of fences did increase marginal vegetation growth at some cross sections.
The fish survey 11 species of fish were caught in 2008 compared to 10 in 2006. There was an large increase in salmon, trout and bullhead, but a decrease in lamprey and minnow. The higher flow conditions in 2008 could be the reason why there was more bullhead and salmon, who prefer swift flowing water, and lamprey and minnow, who prefer more shallow water.
''Hydro-morphological Response''
The physical biotopes mostly glide and a few pools, observed in 2008 were the same as in 2006, with the exception of the created riffles. The riffles had an impact on the sediment regime, with more localized areas of sediment deposition and transport. The exclusion of livestock also decreased the input of fine sediment and an increase in sediment trapping margin vegetation.
The physical channel form was significantly changed by the measures. The depth decreased where the bed of the channel had been raised. However, the higher water level in 2008 minimized the decrease in water depth even at the riffles. Also the change in velocity was minimal due to the higher discharge in 2008 compared to 2006. There was however more coarse material and less coverage of silt.
The complete dataset and more detailed information can be found in the report ‘Physical and biological monitoring of STREAM restoration projects: Year three report’
''Social-economic Response''
The impact of the measures on socio-economic aspects like flood protection are not monitored and therefore unknown. The Hampshire Avon Catchment Flood Management Plan published in 2009 indicates that the area of Seven Hatches is on the border between the Salisbury area with policy 5, Areas of moderate to high flood risk where we can generally take further action to reduce flood risk, and the Upper Avon, Wylye sub area with policy 6, Areas of low to moderate flood risk where we will take action with others to store water or manage run-off in locations that provide overall flood risk reduction or environmental benefits. There are therefore still problems with flood protection that have to be addressed.
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A Memorandum of Collaboration is being signed rather than a Wetland Contract, in view of the current local situation where entities have shown that they are not in a position to commit further resources (man-power and finances) to additional tasks. This is mainly due to the fact that the relevant entities are already committed to execute actions that are currently taking up all their resources and running on very tight budget lines. In order to be able to assign budget, a formal request would need to be put forward by the relevant entities, and approved by central Government for upcoming financial years. Such requests need to be made well in advance. Despite this, stakeholders proved willing to commit to a lower level, via a different form document similar to a Memorandum of Understanding, whereby they express agreement on further collaboration on an agreed list of priorities/actions. +
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A coalition of federal, regional and European stakeholders at the Danube made a large-scale project possble. The large dimension of the project is one of the main ecological succsess factors. +
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A difficulty may be in ensuring that flows in the complex Lower Colne system do not cause flooding elsewhere, as well as the access and cost of the proposed project. It had prior to the last LRAP update in August 2010, been mothballed. +
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A lack of flexibility in the consents meant that a design needed to be rigid before continuation. A better understanding of what is needed from a third party with such limitations in money, availability and future maintenance and accountability would have avoided this issue. To ensure success, we engaged geotechnical services in the design process. Although our evidence was clear from surveys, we needed additional agreement of civil engineers for the EA to be confident our design was appropriate.
Weather was an issue as rain meant rapid water level rises due to the large run-off volumes in the urban area. In addition, numerous weir structures held back large quantities of water. To overcome this, the weir boards were demolished first to allow a free flow of water, and drain the excess ponded areas within reach. Despite a headwater, without first removing the weirs, the water and silt deposits were too deep for safe working.
Working in an urban environment was a challenge due to the surrounding infrastructure and cables. Designs had to be flexible to ensure adjustments to account for this. In addition, there were many landowners (40 individuals) to track down and discuss access and maintenance agreements. +
A number of lessons were learnt from this project, the most important of which was the relative ease with which monitoring data can be collected and used to inform project development and delivery. Where possible WRT and WWCP will now include a monitoring budget in future riparian restoration projects to ensure that similar datasets can be built for other watercourses within the Wyre Catchment.
The project has also allowed WRT and WWCP to build their relationships with a local university. The pre-project monitoring was carried out by a Lancaster University student as part of her Degree course, it is expected that we will be successful in identifying a further student to undertake post project monitoring for a similar period of time to that which was covered initially. The quality of the monitoring which was delivered by the student was very high and ultimately she was highly reliable and required little supervision. This has highlighted the value of working with local universities to us and we will continue to do this in future projects +
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A number of valuable lessons have been learnt through the process of this project, one of the most important being that previous lessons learnt were implemented into this scheme, cutting down on the time it takes to develop and deliver projects. In addition the following form the additional lessons learnt from this project.
* It is not always necessary to engineer river restoration project or provide detailed construction designs, especially in the case of demolition of weir structures in areas of no perceived flood risk.
* Building relationships can lead to cost effective methods of undertaking a variety of river enhancement work, however, all partners must be willing to think a little “outside the box” when discussing delivery options.
* Angling club concerns remain centered around access to the river when water levels are reduced, the creation of berms which slope into the water not only constrict the channel and create flow diversity but also provide year round access to the water irrespective of the water levels. +
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Access was very limited due to the presences of fishing lakes adjacent to the river. Most works had to be completed by hand. Some work was carried out by amphibious excavator where the benefits outweighed the potential damage to the gravel bed from the excavator tracks.
Additional tree works were required due to periods of high winds and the need to make the area safe for construction work to be carried out.
Re-profiled river banks with bare soil were exposed during high flows and could have lead to erosion and sediment input. Seeding and the installation of a biodegradable jute matting was carried out to minimise erosion.
(This had not been anticipated in the design. Ideally work would be carried out early enough to allow bank vegetation to re-establish from the existing seed bank.) +
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According to the Essex Wildlife Trust (2005), the scheme has been effective in safeguarding the local natural environment of the Salcott Channel and the West Mersea Oyster Fishery downstream of the realignment site. The additional monitoring works undertaken at the request of the local oystermen have demonstrated no noticeable effects on their activities.
The natural slope of the site has benefited small fry which have been observed rising through the vegetation with the tide. The gradual slope allows for the zonation of vegetation and provides a mosaic of habitats for a range of sizes and species of fish. The semi permanent pools, which are inundated on high tides, serve as feeding and refuge areas over a tidal cycle. On one occasion, 2000 herring/sprat were caught using a seine net in one tidal pool. This illustrates the value of the realignment site as being beneficial for both commercial and recreational fisheries in the Blackwater estuary.
The tidal regime monitoring (Environment Agency, 2003) determined that no clear evidence of any significant change in upstream tidal levels following implementation was found, which is consistent with the predictions of change (these were of the order of a few millimetres). The general direction and phasing of flood and ebb flows remained unchanged (this was considered unsurprising given the generous configuration of the main drainage channel (Salcott Creek)). There seemed to be a slight increase in current speeds at the station closest to the realignment (as well as a 15% increase at another station). These increases were most marked on the ebb tide as water receded seawards. It was noted that the observed increase in current speeds compared favourably with anticipated increase. The absolute increase in velocity does not appear to have produced any significant erosion of the channel bed. No major hydrodynamic changes were observed in Salcott Creek in the period immediately after the breach (when potential changes would be expected to be most pronounced). By ‘restraining tidal outflow’ the main breach also promoted sediment deposition and accretion which consequently led to elevation increases and vegetation colonisation. The monitoring allayed local fears with regards to sediment concentrations that the realignment could generate ‘sediment plumes’ as no significant increase in sediment concentrations immediately after the breach were observed. This is consistent with little erosion being observed. Monitoring of suspended sediment concentrations was able to demonstrate that the realignment site was acting as a net sink for sediment (with sediment deposition described as ‘significant’) and not as a source and was thus able to dispel concerns associated with accumulations of fine sediment that were reported to occur downstream. The Essex Wildlife Trust(2005) states that ‘it turned out that the ‘problem’ was caused by a new colony of tubeworms and was unrelated to the Abbotts Hall realignment’.
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Accretion: Hagge et al. (1997) note that sediment accretion was not measured as such but it was generally observed that sedimentation was taking place, and that the sinks (i.e. the ring channel and the two depressions created by the sand dredge) were slowly being filled with mud (ca. 5m in the depressions over 10 years). The pensinsula created with the material excavated from the ring creek became an island in 1991 through natural creek evolution.
Fish, benthos and plankton: The fish present in the lagoon were found to be typical of the Wadden Sea, which means that they
can pass through the culverts (which experience average current speeds of up to 4m/s). The benthos and plankton composition was also found to be typical of the fronting intertidal by 1994. The relatively long duration of this establishment period was firstly attributed to the size of the area, but more importantly to the sub-optimal, varying conditions over the first years of the site’s existence (i.e. testing of various tidal regimes and malfunctions of the sluice gates). By 1997, only a few species present on the fronting tidal flats were not found within the site. There were however clear differences between species densities – especially for molluscs. Molluscs were relatively rare in the site, which the authors thought was most likely due to a high predator pressure, who found the habitat to be favourable (young mollusc specimen were found). For polychaetae, the predator pressure seemed lower, as their larvae are produced year round (Hagge et al., 1997).
Birds: With regards to general shorebird use after the land claim when compared to the period prior to it, Atkinson et al. (2001) summarised a report by Hotker (1997) as follows: It appears that only the herbivorous species wigeon and barnacle goose showed increases in the RTE and, even with the remaining intertidal habitats, shorebirds showed a large decline. Only redshank used the RTE for feeding at high tide and the reduction in tidal range, reduced invertebrate densities and enclosure by tall embankments rendered the remaining area unsuitable for shorebirds. As a result of the embankment, the numbers of Brent geese, shelduck and most shorebird species decreased in the area surrounding the embankment compared with pre-embankment numbers. Most species elsewhere in the German part of the Wadden Sea increased or were stable over the same period. Hotker concluded that ‘the lost feeding opportunities due to the land claim could not be compensated in the immediate surroundings of the study site’.
Breeding bird data is available from the site managers’ website (Naturschutzstation Arlau, 2011). The islands in the lagoon have apparently become home to established breeding colonies for several rare birds, including terns, pied avocet and plover. The graph from the image gallery shows how the nine most numerous breeding bird species present in the RTE (excl. gulls) have developed since 1987.
Site functioning/operation: Hagge et al. (1997) concluded that the appropriateness of the saline lagoon as compensation for
the lost habitats had been limited. Apart from it not constituting like-for-like compensation, the system is very sensitive, and requires constant maintenance. For example, scour caused a substantial depression to develop immediately behind the southern culvert, which connects with a more substantial tidal creek than the northern culverts (maximum flow velocities of 5.5m/s occur). Remedial action involved filling this hollow with a mix of 0.5-1.5-tonne boulders and stones (personal communication with sluice manager in 2007). Furthermore, the system is sensitive to long periods of low water levels; these are however frequently required to maintain the embankments to the neighbouring reservoirs and the sluices.
The following recommendations were made for successful on-site water/tide level management, to ensure the area does not suffer from oxygen starvation or extensive algae coverage, and supports a range of habitats and fauna:
* enable maximum, simultaneous, water exchange through both gates;
* enable natural tidal rhythm throughout the whole year;
* enable uncontrolled water exchange to lengthen the life of the sluice technology, and
* simulate a storm surge once or twice a month during the winter months - by damming
water over a maximum of three tidal cycles.
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Accretion: In order for the site to support both mudflat invertebrates and saltmarsh plants, it was important that fine marine sediments would be imported into the site, as these would provide the ideal environment for intertidal flora and fauna. Furthermore such sediment import would ensure that the site would continue to increase in elevation as sea levels rise. Observations from previous managed realignments have shown that sites can accrete relatively rapidly immediately after a breach, but that elevation increases then tend to level off. At Chowder Ness, site elevation monitoring has so far followed a similar trajectory. To date, overall, the site has increased in elevation with the main change in elevation occurring in the initial two years following the realignment.
*Invertebrates: The monitoring has shown that invertebrates have colonised this new sediment. In 2009, between 571 and 15,429 specimens were found per m² (belonging to between 2 and 6 species). The abundance, diversity and biomass of species in the mudflat have been increasing since the realignment has been implemented, and are now similar to the fronting, pre-existing, mudflat sites; in fact, average abundance within the samples collected in 2008 was greater than the fronting mudflats.
*Birds: Shorebirds are making good use of the site; for example, a total of 16 different waterbird species were recorded using the realignment site between September 2008 and March 2009. Species observed in the highest numbers on the site included shelduck, golden plover, lapwing, dunlin, curlew, black-headed gull and common gull.
*Saltmarsh and Grassland: With regards to the development of other habitats, there was a requirement to also create saltmarsh and terrestrial habitats. By 2009, as expected, a small proportion of the site had developed into saltmarsh; this is concentrated along the eastern edge of the site. This saltmarsh is mostly dominated by sea aster, although this is interspersed by other saltmarsh plants commonly associated with the lower marsh, such as spear-leaved orache and sea milkwort. With regards to terrestrial habitats, these were created to support a range of farmland bird species at the top and landward side of the new flood embankment, and along a grassland berm between the base of the embankment and the soke dyke. Within the 2009 surveys, eight bird species were seen to use the grassland, of which six were definitely breeding. These species included moorhen, skylark, meadow pipit, pied wagtail, reed bunting and grasshopper warbler.
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Allow plenty of time for the development and delivery of a large project such as this where the ecological window for delivery is very limited. Involve all stakeholders at the earliest possible stage of development. Due to the sensitivity of the site, archaeology was a major factor and where this is the case adequate funding should be accounted for to the help manage this risk. Future management of the site is very important to ensure that high quality floodplain habitats are created. Here, the tenant farmer will continue with low density, conservation cattle grazing. The project was carefully designed to not back up any water onto the field immediately upstream. +
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Although the dead wood method yielded no results in this particular location, it has since been applied in various other projects and is generally well received by society. An important lesson is that a sufficiently high discharge is required for this measure to function. Projects such as this one can be complicated by a shortage of available wood and problems cleaning out debris. It has also been noticed that willow wood is less suitable for this measure, as it degrades quickly and is likely to sprout. +
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Although the method yielded no results in this particular location, it has since been applied in various other projects and is generally well received by society. An important lesson is that a sufficiently high discharge is required for this measure to function. Projects such as this one can be complicated by a shortage of available wood and problems cleaning out debris. It has also been noticed that willow wood is less suitable for this measure, as it degrades quickly and is likely to sprout. +
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An early challenge for this project was to influence the owners to agree to a major landscape change within the Grade 2 listed site. This was achieved by presenting to them the advantages of creating a natural and sustainable river system and the abandonment of an unsustainable and ecologically impoverished ornamental lake. Lesson learnt - engage early with the landowner.
The next challenge was to deal with the constraints of the site including:
• Funding
• Heritage
• Ecology / SSSI features
• Planning / permitting process
• The moat
The planning process added approximately 6 months to the project. We did not foresee the challenges made during this process nor the length of time it would take to bring the process to a close. Conditions imposed added time and costs to the project.
Funding presented a challenge as is always the case with restoration projects. Funding was sourced from the EA, NE and the Trustees of the Tichborne Estate.
The ornamental moat previously relied on an outflow from the lake. This project incorporated a major restoration of the moat to isolate it from the Cheriton Stream.
The heritage and ecological requirements were dealt with by engaging suitably qualified consultants so that the designs were suitable to achieve the necessary permits and permissions. +
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Applying an ecosystems approach form the start could have attracted more partners funds and benefits and avoided any negative impacts. +
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Applying nature based solutions in the current consenting and permitting environment is not easy. Water and wildlife need space and the current land management payment systems and permitting and consenting process needs to be changed and/or adapted to reflect more dynamic river systems that are given space to evolve. In certain places within our river systems we need to move from drainage to habitat and the regulatory and funding environment needs to be changed to enable this to happen. +
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Archaeological considerations and heavy rainfall/flooding both caused considerable delay and a change in the scope of this project. Due to the proximity of the Stonehenge World Heritage site, English Heritage was not happy with the original restoration plan, so the project was delayed to re-plan. During this time the area received record rainfall, leading to flooding which prevented work from being undertaken. For future projects, further time should be allowed to fully investigate potential archaeological issues and allow for bad weather/environmental delays. +