Case study

Newlands Common Sustainable Drainage System

The heavy flooding around Britain over the last couple of years make the question of how to provide the 28,000 new house per annum required by the South East plan, without exacerbating existing flood problems, a difficult one.

Transport Planning
Infrastructure Design
Environmental Assessment

Details

Project

It is now widely recognised that land use plays just as important a role in the origin of flooding events as the weather. In a “greenfield” environment, rainwater falls on the river catchment and a significant proportion percolates through to the soil. The proportion that does not recharge the groundwater table evaporates or eventually ends up at the outfall point of the catchment. However, the increased urbanisation of catchments has resulted in the loss of this natural control mechanism. With the result that rainfall is now being much more rapidly conveyed to the outfall point, thus creating a large peak flow, much increased total volume and potential flood conditions. The other issue with these pesky “run-off’s” is that the rush of water entering the outfall from the urban catchment usually brings with it a rush of polluting substances. This can result in the deterioration of the area around the outfall and the loss of species both there and downstream.

Sustainable drainage systems or SUDS are an alternative approach to the management of surface water drainage, which strikes the balance between the management of surface water run-off and the need to conserve natural resources. While SUDS techniques are becoming more and more common in construction projects, there has been limited research in the UK, the South in particular, on the results of implementing SUDS, and the success with which is achieves a more ‘natural’ drainage regime.

Challenge

A 298-hectare area of farmland to the West of the town of Waterlooville in Hampshire, known as Newlands Common, is one of the sites that was identified in the South East development plan as being suitable to provide around 2,000 of the new houses required. The site is located within the upland catchment of the river Wallington. Therefore, for an application for development of this site to be successful, it was imperative that all of the stakeholders were satisfied that on-site flooding and downstream impacts would not be an issue.

From the outset of this particular project, it was recognised that if the principles of SUDS were properly applied and if all stakeholders were brought to the table at the earliest stages of design, it had the potential to become a national case study for SUDS and what can be achieved.

The Newlands Major Development Area (MDA) therefore presented a major opportunity to study pre- and post- development effects of SUDS.

This opportunity was recognised by project engineers Mayer Brown, site owners Grainger plc and the Environment Agency (EA) and as a result a unique partnership was forged in order to use the MDA as a research project. The University of Portsmouth later joined the project and with funding from the South East England Development Agency (SEEDA) employed a Research Associate for the project. The Research Associate was based in Mayer Brown’s head office in Woking to work alongside their design and construction supervision teams.

Regular meetings took place including all of the major stakeholders (Grainger plc, Mayer Brown, the EA, Southern Water, Winchester City Council, Havant Borough Council and Hampshire County Council) to develop acceptable drainage strategies which incorporate the ideologies of SUDS, as well as providing a forum to discuss public adoption of SUDS.

Major obstacles had to be overcome, which centred around the SUDS design criteria and maintenance issues. Wesley Jones, a Development Control Specialist for the Environmental Agency stated, “It is unique in the fact that we have collected baseline data for the catchment over four years. Therefore we are in a very special position to analyse what effects the development will have on the catchment hydrology, water quality and biodiversity. The project will show how SUDS mitigate against the effects of urbanisation and will highlight how SUDS can reduce flood risk, protect waterways against diffuse pollution and enhance the environment for wildlife.”

Solution

This research will make a major contribution to increasing the understanding of the treatment processes in SUDS and provide case study material to promote their use at other new developments. The client Grainger Plc has been very satisfied with the outcome of this long term consultation and design process.

“Being a pioneer on a large scale SUDS system such as the Newlands project is not for the faint hearted. If the project hadn’t had the determination from all parties we would have probably ended up with a traditional drainage solution,” said development officer John Beresford. The full commitment of all the major stakeholders created the opportunity to consolidate all aspects of SUDS into this one project.

Developers are not adverse to SUDS usually the resistance arises because of the bureaucracy and red tape between the authorities. This usually relates to who will adopt the SUDS system and fear of the unknown. We are hoping that as a result of the Newlands research project we’ll see a guidance note ‘SUDS for adoption’ which will see others incorporate SUDS into their development projects.

The ongoing research work at Newlands is already feeding into the design and construction of the swales and lakes that will become part of Newlands Common. It is hoped that this large-scale scheme and the commitment demonstrated through this project will provide the impetus for other developers and authorities and hopefully help towards preventing the cost and chaos of flooded homes in the future.


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