Strategies involved when developing new networks

Clare Hobson, Brian S McIntosh and Paul Jeffrey from Cranfield University's School of Water Science analyse the demand for water during the infrastructure planning process

As one of three case studies in the EC-funded TiGrESS project, the School of Water Sciences at Cranfield University, in partnership with Exeter University and Three Valleys Water, is carrying out research to look at the relationships between regional land-use change and water supply infrastructure performance and investment.

While the treatment and infrastructure networks that provide potable water and treat wastewater are largely fixed-in-space, the communities and built environments they serve are constantly changing. Therefore there is a need to coherently relate planned housing development at the regional scale with water supply infrastructure planning. Government plans for the economic development of the south and south-east of England make provision for large-scale commercial, housing and industrial development along the M11 corridor, which runs from north-east London, to the city of Cambridge.

This area has sustained substantial economic growth over the past decade and recent housing pressures have become intense, prompting government plans for up to 500,000 new homes1. The Environment Agency has warned this may mean water shortages for the south-east where water companies are already planning new reservoirs in order to meet current demand2. Consultants Levett-Therivel agree the water supply infrastructure does not have the capacity to cope with the proposed increase in population and development plans are likely to have a serious negative impact in terms of water shortages3.

Figure 1 illustrates some of the interactions between water resources and planning at both ground and management level. At ground level local authorities have planning control over the location of water infrastructure such as WTWs and reservoirs. Water companies use the planning system to assist them in predicting the scale, location and timing of new demands. In return, areas of excess water capacity may influence which areas are selected by planning authorities for development4. However, interaction is not formalised and the concerns raised following the government's announcement of proposed housing development in the south and south-east have highlighted communication problems between the land use planning and water management sectors4.

Reliable projections of future water demand are essential for the design of water supply networks as either over or under-capacity in the system can lead to significant financial, environmental and economic costs. To avoid future water shortages in the south and south-east, and better relate land use planning to water supply capacity, both land use and water supply planners may benefit from forecasting methods that take into account changes in property numbers, and that are based on the information easily available during regional planning processes. The primary objective of the work being undertaken is to develop a spatially discretised strategic water demand and supply analysis tool, termed Infraplan. The purpose of Infraplan is to provide a platform for water supply companies, regional planners and water resource managers to explore relationships between land use change, water demand, and the expansion of water supply infrastructure.

As part of the process of developing the water demand component of Infraplan (Figure 2), the School of Water Sciences has analysed water consumption data from a set of metered households in Stevenage, a town within the M11 corridor. The objective of the analysis was to determine to what extent it is possible to explain variation in water demand using the characteristics of the development listed in Table 1, rather than of the people who populate it. Univariate statistical techniques were applied to 24 months of daily water consumption data in order to establish whether the water consumption varied significantly with any of the housing characteristics examined.

Property type was observed to significantly influence both peak and average components of both winter and summer demand. Flats and cluster homes were observed to consume the lowest quantities of water, while detached properties are the highest water users (Figure 3). In respect of the other property types, terraced and semi-detached properties can be said to have medium water consumption. In combination with analysis of the relationships between other property characteristics (Table 1) the Cranfield University team has developed a stochastic simulation model of water demand for different household types and other land-uses including retail, industrial, etc. The model has been integrated into the Infraplan tool and is capable of generating monthly water demand values for different land uses, based upon simulated changes in regional land-use distribution across a 50km x 50km portion of the M11 corridor.

Through the development of a range of regional development and infrastructure investment strategy scenarios the TiGrESS M11 corridor team plans to use Infraplan as a means of facilitating informed dialogue about strategic water resources management. In doing so it should be possible to investigate the impacts of different infrastructure planning and cost recovery horizons on supply capacity at a much earlier stage in the regional planning process than is currently possible.

References: 1 Office of the Deputy Prime Minister (ODPM) Sustainable communities in the south-east: Building for the future. Office of the Deputy Prime Minister's Publications, London, 2003. 2 P Hall, Hot Potatoes and Bad Omens (Serplan's sustainable development strategy for the south-east). Town and Country Planning, 1998, 67 (6) 1998. 3 BBC News, New homes could mean water bans, http://news.bbc.co.uk/1/hi/uk/3556644.stm. Thursday, August 12, 2004, 04:19 GMT. 4 S Slater, S Marvin and M Newson, Land Use Planning and the Water Sector. Town and country planning review 1994, 65 (4) 375-397.

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