When EIA influences design - A case study

23rd December 2014

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Naomi Warr

Arup offers an example of successful design modification to mitigate a reservoir development's environmental impacts

All practitioners know that EIA is intended to be iterative such that it positively influences the design of proposed developments with the aim to either design out potential negative impacts or to substantially reduce them. When it succeeds, this results in a more holistic design that benefits the design team, assessment team, the client, natural habitats and ultimately the people who live and work in and around the proposed development.

Bristol Water’s Cheddar Reservoir Two is a prime example of such a success. The reservoir site is south of the existing Cheddar Reservoir and covers an area of 210 hectares. The existing site is largely agricultural land and the Cheddar Yeo river forms its southern boundary. The proposed reservoir, including the embankment, would span 1400 metres north-east to south-west and would be approximately 900 metres wide at its narrowest.

Part of the reservoir footprint was unavoidably located in flood zone 3, so an area of compensatory flood storage was set aside to the west of the reservoir. In the initial design, this area simply provided flood storage. However, as the ecological and cultural heritage surveys progressed, it became evident that in the absence of mitigation, there could be significant negative impacts on a number of habitats and species including European protected species. In particular the proposed development and surrounding areas provided foraging habitat for a number of bat species and included areas of high cultural heritage potential. There was also a need to establish effective landscape design to ensure a seamless fit with the existing reservoir and agricultural environment.

The project team initiated a series of detailed, interdisciplinary meetings between the project engineers, ecologists, heritage experts, hydrologists and landscape architects, which integrated the different mitigation requirements into subsequent designs.

Habitat creation in the flood compensation area as well as the wider development area was a big part of the design mitigation and included changes to the project design to include a stream diversion - with an artificial nesting bank suitable for kingfishers, creation and enhancement of new and existing rhynes (drainage ditches), reinstatement of a duck decoy - a pond historically used to capture wild ducks and designated as a scheduled monument and the creation of a wetland area, incorporating wet woodland.

In addition, five kilometres of hedgerow was identified for translocation, nearly 60 hectares of species rich grassland created, and improvements to the River Cheddar Yeo were identified to improve the morphology for the proposed flow regime. In depth consultation with statutory bodies was key to reaching agreement on these mitigation measures to reduce negative effects of the proposals to levels that were assessed as not significant and therefore remove barriers that would otherwise hinder development.

As well as reaching agreement with the statutory authorities, overall agreement for the integrated design mitigation within the project team itself represented a huge success not only in getting the project approved but also as a testament that intelligent, well-thought-out and integrated design can lead to improved natural environments. Conflict between different members of the project team - in particular between the design and environmental assessment team - can be resolved by early and continual involvement of environmental specialists so that their assessment work and proposed solutions can be fed into the design.

Mitigation must be deliverable and therefore the ownership of land or agreements with landowners to host mitigation is important. In this instance, the design team therefore worked extensively to integrate all mitigation and enhancement into the required land holdings for the new reservoir. Bristol Water facilitated this process by working closely with the design team, removing the need for offsite mitigation for the habitats that were lost under the reservoir footprint. Where this is possible, it represents a huge bonus for projects which may struggle to find suitable sites for mitigation of ecological effects.

Design mitigation would have been severely restricted if the EIA team had not identified the constraints and potential mitigation early on and been able, permitted and encouraged by the client to work alongside the design team to positively influence the final design.

As EIA practitioners we need to be more confident and possibly more dynamic in the way that we influence designers. Mitigation solutions don’t necessarily mean significantly higher costs but will lead to better, more complete designs that not only get planning approval, but actually fit into the paradigm of sustainable development.

Arup Associates is a global firm of consulting engineers, designers and planners.


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