David Kingsley-Rowe, senior environmental scientist at Cascade describes how to ensure accurate survey data to aid the definition of the baseline and provide the basis for identification of mitigation measures.
Cascade, a practice of Ricardo Energy and Environment, provided ecological support during the EIA for a planning application for flood defences near Lydd in Kent.
The Ministry of Defence (MoD) firing ranges at Lydd support a variety of coastal habitats, most notably shingle vegetation. These range from ancient stable acidic calcifuge grassland through to communities that are more maritime in nature, reflecting the retreating coastal frontage.
The site contains the most diverse and most extensive examples of stable vegetated shingle in Europe and is designated as part of the Dungeness SAC and Dungeness, Romney Marsh and Rye Bay SSSI. It contains both annual vegetation of drift lines (AVDL) and perennial vegetation of stony banks (PVSB).
In the UK, there are only a handful of sites where these habitats are the primary reason for designation (four for AVDL, and seven for PVSB). Many of the habitat variants are considered to be practically irreplaceable due to the time it would take them to recover from disturbance.
The flood defence work proposed by a joint venture between VolkerStevin, Boskalis Westminster and Atkins (VBA) would reduce flood risk by stabilising the beach and extending the inland embankment structure known locally as the ‘green wall’.
However, the construction of the flood defence would unavoidably impact designated habitats and it was critically important, as part of the ecological assessment within the ES, to understand not just the area of loss but the habitat variants within the construction zone so that appropriate compensation sites could be identified.
Flag Ecology were contracted to undertake the specialist shingle surveys and mapped the wide variation of sub-habitats in intricate detail (see image). This was a time-consuming and costly exercise with in excess of 60 days required to survey and map habitats within around 150ha. However, this hugely intensive work was absolutely necessary in order to identify the broad habitats and sub-communities, including at scales as small as 1.5m2.
Example SAC habitat map
An accurate understanding of potential losses is important on any site but when dealing with incredibly rare irreplaceable habitats, which can be damaged just by driving over them once, it is vital to understand distribution and extents. An extra complication was the need to consider the impacts of sea level rise and the habitat loss (or change) that is likely to arise from coastal squeeze. The proposed flood defence improvements have a life of at least a 50 years and so it was important to understand and reflect in the EIA these additional losses to ensure they would be adequately compensated for, even if the effect would not be felt for several decades.
Post-survey, significant GIS work was undertaken to verify and confirm the data, specifically habitat extents and condition. This detail was used to identify the needs for on-site mitigation (such as haul routes) but was also key in shaping discussions with stakeholders (MoD, Environment Agency and Natural England) and agreeing appropriate compensation for the scheme.
Due to the site’s designation as an SAC, any losses incurred as a result of the scheme (both from construction and from coastal squeeze) would have to be compensated for at an off-site location. The rarity of habitats both nationally and locally meant that this was always likely to be difficult, and relied on the accurate surveying of the site in order for the compensation requirements to be clearly understood.
After compensation areas had been identified at other locations it was necessary to demonstrate that where a specific sub-community was likely to be lost or damaged, the compensation site had the same or very similar habitats. Further survey effort was put into comparing the condition of both the communities under threat and the communities acting as compensation.
Without the comprehensive surveying and GIS work, the information on the baseline would be lacking and it would have been more difficult to identify, assess and mitigate for the construction impacts within the EIA. This work has also enabled the identification of appropriate compensation areas which will assist decision makers when considering the planning application.
