Something in reserve

Bristol Water’s proposed Cheddar Reservoir Two is a major part of the company’s long-term water resource plan. Phil Hodgson and Rick Grosfils look at some of the detailed work behind the plan.

Driven by increasing demand, water security is a growing issue and, although water may currently flow abundantly from our taps, it is a valuable resource and our future supply needs to be safeguarded.
In December 2013, Bristol Water submitted a planning application for a 9,400 million litre reservoir in Somerset, near the existing Cheddar Reservoir. This artificial lake, known as the Cheddar Reservoir Two, is an essential part of Bristol Water’s long-term water resource plan. It is forecast that the population in Bristol Water’s supply area will increase by 36 per cent, from 1.1 million in 2007 to 1.5 million in 2035. The second reservoir, as part of a balanced approach including cutting leakage further, encouraging water metering and helping customers save water, will help secure a major new water source for 50,000 homes in the
local area.
Following more than three years of analysis, careful planning and the recent submission of the planning application, there are numerous other steps to follow. Alongside seeking approval of the local authority, regulatory approval is needed from Ofwat, the water industry economic regulator, confirming that this proposal is the best choice available and represents real value for money for customers.
Bristol Water worked with Arup from August 2010 to select the optimum site for a new reservoir, assess the reservoir’s potential impact and prepare a scheme for its development. The combined team found a balanced solution through local insight and an integrated approach to water management problems.
The site for Cheddar Reservoir Two, immediately south of the existing Cheddar Reservoir and near Cheddar Village, was chosen as the preferred location after detailed technical studies and stakeholder consultation. Starting with an initial 53 sites, a “long-list” of 36 was established based on practical issues such as topography, environmental designations and protected sites. The 36 sites were individually investigated against 20 criteria, including ecology, engineering construction, visual and access – leaving a shortlist of six.
A detailed assessment was undertaken of the shortlisted sites, with trial pits and boreholes, habitat surveys, cultural heritage studies and whole-life costing assessment. The wider economic and social benefits that the scheme could bring to the favoured locations were also considered. The chosen site benefited from good ground conditions, available and suitable material to build the reservoir and good proximity to the existing water supply network. The site also offered the opportunity to enhance the social and ecological amenity of the area.
Bristol Water had a strong vision for the scheme, which was to ensure the security of future water supplies, but also to incorporate a wide range of social, environmental, amenity and recreational opportunities for the surrounding area.
Extensive environmental surveys and studies were undertaken to baseline the environmental impact assessment, and to influence the masterplan. For example, the reservoir footprint was aligned to safeguard mature trees and hedgerows, accommodate utilities and a river diversion, along with pedestrian, cycle and disabled driver access. An extensive archaeological investigation including geophysics surveys and trial trenching investigated this potentially rich archaeological area. This resulted in the proposed reinstatement of a 17th Century Duck Decoy (originally a structure for capturing wild ducks for food) as an integral part of the masterplan.
Although the location selected for the reservoir offers a range of benefits, it also poses unique challenges. Sitting partially within the Environment Agency’s Flood Zone 3, compensation for the floodable area lost is needed. This will involve slightly lowering ground levels across an area adjacent to the reservoir to increase the flood storage volume of the available land. However, this area serves multiple purposes because it was designed to encourage biodiversity, provide a habitat for local wildlife and create a quiet amenity space for visitors.
The local community has played an important part in the process. A consultation plan was drawn up in discussion with Sedgemoor District Council, and a two-stage consultation strategy implemented. This allowed views and ideas to be openly expressed, considered, and where appropriate incorporated within the masterplan. Each stage included three days of public exhibition and design workshops with community representatives and statutory authorities.
The design solution avoids adverse impacts, integrates mitigation and responds to the opportunities for environmental enhancement. Arup supported Bristol Water with this planning application by bringing together a team of specialists in project management, town planning, public consultation, reservoir design, landscape design and environmental assessment. Arup implemented a project structure that integrated disciplines and progressed with work in managed phases. This approach, coupled with close co-operation with Bristol Water staff throughout, encouraged inter-­disciplinary collaboration to resolve issues and pursue opportunities in a timely manner. The planning application is currently being considered by Sedgemoor District Council, and a decision is expected later
this year.