OXFORDSHIRE WATER RESOURCES

Analysis and policy recommendations by SOS expert Water Group

Summary This paper describes the current state of the County’s water resources and how they are determined. It addresses the problems of too much water and too little, in terms of flood, drought and water supply, at these time of climatic change and when a large and rapid rise in the population is proposed by the Strategic Housing Market Assessment (SHMA). It concludes with recommendations for action.

One of the most rural counties in South East England, Oxfordshire is also one of the driest in the UK. It occupies much of the basin of the upper Thames, an area of 2605 sq km. The present population is estimated to be 666,100, giving a density of 255 per km sq, slightly less than the figure of 260 for the UK as a whole. The County contains geologically contrasting areas of impervious clay and Chalk and limestone. These measures form the Chilterns, the Berkshire Downs and the Cotswolds where large volumes of groundwater are stored.

Information about the state of the water resources in Oxfordshire has a long history going back to the early 1800s. It is collected on various time scales from minutes to months from the network of instruments and monitoring sites strategically located across the County. Included are: raingauges, weather stations, installations to measure river flows and water quality, together with sites where soil moisture and groundwater levels and groundwater quality are measured in observation wells and bore holes. The Environment Agency is responsible for collecting, processingand analysing these observations, with the Met Office, which also operates the weather radar network, and the satellite imagery over the County. Thames Water is also involved, along with CEH Wallingford and a number of other bodies which collect and contribute water resources information

Under average conditions, the difference annually between rainfall and evaporation ensures an adequate flow in the Thames and its tributaries and the maintenance of sufficient soil water and the recharge of ground water. Dry weather during the summer decreases this difference to cause reductions in flows and less water to be available to the soil and ground water stores. Drought exacerbates these conditions, especially when it extends over the winter, or several winters, such as between 2010 and 2012. Over a 10-year period these conditions may apply during one to three years. Above average winter rainfalls increase flows in the Thames, raise soil water contents and increase ground water levels. Rapid increases in flows are notable in clay areas, while ground water levels rise more slowly on the Chalk and limestone where the volume of water stored is immense. When intense and localised storms occur, such as during the summer, flooding follows, especially where the soil is so dry that percolation is inhibited and where paved areas are extensive. The increase in the latter in recent years has exacerbated this problem, as has lack of maintenance of streams and watercourses. Extended wet periods during the winter cause flooding on a larger scale, while rapid snowmelt, such as in spring 1947, produce the highest peak flows. However current projections of climate indicate milder winters with more rain, so that snow melt floods are less likely to occur. The City of Oxford, Abingdon and several other Thames-side settlements have experienced several periods of flooding in recent years. A flood relief channel is planned for the west side of Oxford to reduce the risk to properties in the City. However there is anxiety amongst some that flood levels will increase downstream as a result.

Preventing flooding in Oxfordshire is the responsibility of the County Council and the Environment Agency through the work undertaken on river courses, streams and drains, such as by the construction of embankments and employing barriers. Slowing down the movement of flood water by making channels more sinuous, recreating wetlands as epitomised by the River of Life Project provide another dimension.The County Council also distributes sandbags along with the District Councils. The Agency issues flood warnings and has prepared a flood risk map of the County so that home owners can understand what level of danger they are exposed to. This map, constructed from analysis of recorded floods, has been the basis for the advice provided by the Agency on planning applications considered by the City and District Councils. Proposals for developments in areas shown to be at risk may not have all been turned down in the past .Now the floods experienced in recent years suggest that the magnitude/ frequency relationships are changing and that risks have risen----the 50 year flood (the flood on average expected to be experienced once in 50, years) may now be the 25 year flood. Consequently a greater part of the County must now be considered unsuitable for development. In addition there are significant areas which are subject to local floods from poor surface water drainage, to flooding from sewers and to groundwater flooding especially where the unwanted water cannot drain away.Where such flooding occurs is an important restriction on development.

Water services within Oxfordshire are largely the responsibility of Thames Water. Water supplies are delivered to households, farms, hospitals, academic bodies, businesses and industrial enterprises, such as the BMW plant at Cowley. Some households rely on a private supply The major sources are Farmoor Reservoir, and the Gatehampton well-field at Goring. Water mains, pipelines and conduits carry this treated water to customers. Much of this network is more than 50 years old, demanding continuous attention because of leakage. Leaks may cause the loss of 20% or more of the water put into supply. There are large transfers of water out of the County from Farmoor and Gatehampton to Swindon. After use and treatment, much of Swindon’s water is released into the upper Thames. Thames Water’s sewers carry the waste water away from consumers to be treated in waste water treatment works. The treated water is discharged subsequently to the Thames and its tributaries. The existing capacity of the County’s sewers and treatment works will have to be increased considerably to cope with the extra 100,000 households and the sources of employment associated with them. Some households employ septic tanks which need to be emptied regularly. A large volume of water is extracted from the Thames at sites downstream of the County, notably to provide the supply to London. Recycled water makes up a large part of the water put into supplies in the County and in the Thames Basin, requiring careful monitoring of abstractions to maintain quality. The levels of nitrates and phosphates have presented a problem for some time,but new ones have been emerging, such endocrine disruption in male fish and cyanobacteria blooms which can be toxic. With several hundred new chemicals entering the environment each year, vigilance is required especially where micropollutants are concerned. Are quality problems being built up which will only be revealed at some time in the future?

Water consumption across Oxfordshire is currently above 140 litres per head per day and the metered charge for supplying domestic water and carrying away waste water is some £1.20 per cubic metre. Some properties are metered, the remainder being charged an amount according their rateable value. Thames Water encourages home owners to install meters and promotes the use of devices which lower consumption. The hope is that perhaps by 2030 water use can be reduced to 100 l/h/d per day. However, even if this reduction is realised, with the anticipated increase in the County’s population the overall demand for water will rise by at least24 million litres per day. By increased metering, pressure reduction, improved leakage control, increasing the charge for water and continuing publicity campaigns to save water, this demand may possibly be met from existing resources during average conditions. However dry weather and prolonged drought will increasingly stress the resource and require more stringent measures, such as shutting off supplies at night and/or to selected areas of the County. Indeed hotter summers are likely to increase the demand which may also rise with living standards. Climate change scenarios indicate that summers will become hotter and that dry periods will be more frequent, leading to the argument that existing resources need to be augmented not simply for Oxfordshire, but also for meeting downstream demand, particularly from London. A large reservoir near Abingdon is considered to be one solution,along with its connection to the River Severn, the enlargement of reservoirs in Central Wales and the operation of the whole as a water resources system.. This long term solution would be costly. It would require agreements across boundaries of the type that have not been applied in the England previously where most water resources development has been confined to single river basins. It would raise questions about the significant increase in the capital value of Thames Water with its foreign owners. There would also be considerableenvironmental problems, such as those concerned with the maintenance of sufficient flow in the Severn during dry periods and water quality differences between the Severn and Thames basins.

The ambitious plans to increase the population and housing across Oxfordshire envisage by the Strategic Housing Market Assessment (SHMA) will put considerable strains on water supplies across South Oxfordshire and the Thames Valley. These supplies are already at risk during extended dry periods (such as that experienced between 2010 and 2012) and climate change is expected to exacerbate these risks further. Water metering might help, but to reduce individual water use from 140 to 100 litres per day would require considerable behavioural change as well as investment into low water use systems and rainwater harvesting. Major infrastructural solutions, such as a new Abingdon reservoir or transfer of water from the River Severn will be controversial, expensive and come with environmental problems. In addition a major new reservoir would result into a substantial loss of farmland and a substantial change in the rural nature of west Oxfordshire. Currently many small villages lack adequate waste water systems and developers are reluctant to pay for their extension to handle the effluent from new houses. New waste water problems will arise from the large scale development which is proposed

RECOMMENDATIONS

While there is no one simple solution to Oxfordshire’s water problems a few basic principles should be followed:

  1. The County Council, the City and District Councils, the Environment Agency and Thames Water should review the adequacy of the resource to meet future demand for domestic and industrial water use over the coming 50 years for both the county and demands lower in the basin. The limitations of water supply thus identified must be considered in future revisions of the Oxfordshire Strategic Economic Plan and related Strategic Housing Assessment. This is in line with the guiding principles of the NPPF of ensuring development is within environmental limits.
  1. Future housing and industrial development must include water saving measures, including water harvesting, grey water use and low use appliances.
  1. There must be no development on the County’s flood plains. The County Council and City and District Councils with the Environment Agency should review existing flood risk maps and identify those areas where development will be hazardous because of expected changes in flood frequency in the next 50 years. In cases the cost of retrofitting flood protection measures should be borne by the developer.
  1. Strenuous efforts should be made to increase the natural water storage in the basin (such as wetlands, SUDS, farm reservoirs). Sustainable arrangements must be made to provide for the continuing maintenance of existing and planned systems.
  1. It should be recognised that the future is likely to bring substantial water quality problems and increasing volumes of water are reused and new pollutants, with unknown health effects, emerge.

There is an opportunity to achieve sustainable development within Oxfordshire. However in reaching this goal it must be acknowledged that there are increasing risks from flooding and from water shortages. Future development plans should take serious account of the considerable environmental limits which water imposes.

Our experts welcome the opportunity to discuss further the issues raised in these notes.

SOS Water Group, March 2 2016

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