description of region | water resources | past droughts and floods in the Thames region | climate change and hydrological extreme events
changing land use patterns and flood risk | development, demand and the production of water scarcity references

Southern England is the most densely populated and driest region of the UK. The largest river, the Thames, supplies the majority of the population. The water industry was privatised in 1989. The effect of privatisation has been new institutional arrangements in the regulation of the water industry. While continued improvement in wastewater treatment is an issue, the main challenge for water utilities in southern England is balancing supply and demand. The hot summer and drought of 1995 highlighted the vulnerability of water supplies to large scale climatic disruptions. Policy questions include:
  • What factors influence domestic demand for water, both in reducing short-term peaks and long-term use?
  • How can demand management, as an institution of rules, strategies and shared norms among diverse stakeholders, ensure reliable water use?
  • What institutional arrangements result in various alternatives for augmenting supplies?
  • What is the residual risk of water scarcity, after demand management has been implemented?

3 main issues

  • continued improvement in wastewater treatment
  • balancing supply and demand
  • ensuring reliable water use through demand management, as an institution of rules, strategies and shared norms among diverse stakeholders

description of the thames valley

The Thames region is approximately 12 900 km2 in area, with an average yearly rainfall of 690 mm [1]. Approximately two-thirds of the catchment is permeable, consisting of chalk, middle Jurassic limestones, and river gravels, and is thus subject to direct recharge from rainfall. The remaining third of the catchment consists mainly of low permeability strata, such as clay; here, surface water runs off directly into watercourses [1,2]. The watershed represents less than ten percent of the land area of England and Wales, but contains twenty-three percent of the population, generates just over twenty-seven percent of GDP, and has a similar percentage of all construction work [3].

The river basin is conventionally divided into four areas: the tidal, lower, middle and upper Thames. The Upper Thames flows from Thames Head (its source) to its confluence with the River Windrush at Newbridge, falling 46 metres over a distance of 64.7 km [4]. The Middle Thames runs through the first major cities along the river — Oxford (population 120,000), and into Reading [5]. The first major discharge of effluent directly to the Thames occurs in this stretch of the river — below Oxford.

The lower Thames runs from the confluence of the River Kennet in Reading to Teddington weir — the official upper tidal limit of the Thames [6]. In this stretch of the river, the flow of the Thames is supplemented both by springs and seepages rising from the chalk aquifer, and from tributary flow; run-off from clay is important near the Teddington weir. At Teddington, the freshwater flow in winter may exceed 30,000 Ml/day; but this flow decreases significantly in summer, and has been known to dry up completely (e.g. during the 1975/76 drought) [7]. Under normal conditions, the Teddington flow is maintained at a minimum of 800 Ml/day, but this may be reduced to 200 Ml/day during times of drought. Urban run-off, discharges from major sewage treatment works, and tributary water of only ‘fair’ quality all contribute to declining water quality in this stretch of the river, as compared to the upper reaches.

The tidal Thames, from Teddington onwards, flows through central London, widening from less than 100m in the upper reaches to more than 7 km at Southend. Discharge of treated effluent from London occurs mostly downstream of the city itself. Water quality in this final stretch of the river is carefully monitored [7].



water resources

Water resources in the Thames region are supported by groundwater, which provides a considerable base flow component to many rivers, particularly in the upper reaches of the catchment. The River Thames is the only major river in the catchment; the basin is unique in England and Wales in that the public water supply network is reliant on one major river for water supply. The Thames functions as a reservoir running the length of the catchment, supplying more than half the total demand for water through direct abstractions [1,8]. Approximately 55% of the effective rainfall within the catchment every year is taken up into the water supply system, more than three quarters of which flows to the water supply of 12 million people.


past droughts and floods in the thames region

The Thames region, together with the UK as a whole, has experienced four major dry periods in the last twenty years: 1971 to 1976 (with 5 dry years out of six), 1984 (February to August), 1988 to 1992, and 1995 to 1997 [9,10]. As water resources are groundwater-supported, single-season meteorological droughts affect water resources in this region less than in other regions in the UK. Multiple season, or multi-year (‘back to back’) meteorological droughts, such as the period from 1995 to 1997, are a more typical cause of hydrological and agricultural droughts. The most recent groundwater drought is the most severe since records began; many boreholes were at or below historic minima in 1997 and the early months of 1998.


climate change and hydrological extreme events

The impact of climate change on both water resources [11] and demand patterns [12] has recently been integrated into water management planning in England and Wales. With the publication of the UK government’s Review of the Potential Effects of Climate Change in the United Kingdom in 1996 [13], the relationship between water resources and climate change began to receive more attention. In the same year, the economic regulator of the water industry announced that climate change, formerly excluded from consideration in the economic regulation process, would now be taken into account in the next review of water company performance.

With regard to the possible implications of climate change, analysis has been carried out on peak flood levels recorded along the Thames over the past one-hundred years [14]. This show that there has been a nearly constant rate of occurrence of flood events above a bank-full threshold, although a greater number of extreme events occurred in the first half of the record, i.e. before 1940. Channel dredging and flood prevention schemes have resulted in a localised decline in peak flood levels and event duration.

However, GCMs (Global Climate Models) suggest that precipitation and runoff in the UK will increase in all areas except south east Scotland [15]. This could indicate increased flooding problems on major rivers like the Thames, particularly since the precipitation increase is a winter phenomenon, and most floods on these rivers occur in winter. The 2050 scenario indicates increased runoff of between 15-25 percent for at least two thirds of the Thames catchment (the remainder seeing increases of between 25-100 percent). Existing flood control schemes would be seriously underdesigned in the face of such changes; and current insurance arrangements may no longer be adequate - as event claims may increasingly go into the domain of re-insurance. For example, if the changes for the river Thames increased the flood depths for the 100 year event by just 100 mm, the increase in damages caused by that event (on the Windsor to Teddington reach alone) would be from £49.3 million to £64.3 million, or an increase of over 30 percent.


changing land use patterns and flood risk

The Upper Thames flows through a predominantly rural landscape and does not pass through any major towns. However, the Middle Thames, from its confluence with the River Windrush to Teddington at the head of the Thames estuary, the runs through a predominantly urban landscape as set out above [16]. Warning times in the upper parts of the catchment are limited to hours, extending to days in the lower areas, depending on the use made of rainfall forecasts. The catchment has changed dramatically over the last century. Crooks (1994) [14] summarises these changes under three headings:

  • Channel dredging and clearing of all the main water courses during the 1930s and 40s - the tributaries before this time were in a very overgrown state. The results of these works on the tributaries would be to increase the rate of flood runoff into the main river.
  • Increasing urbanisation and the development of new towns - increased runoff
  • Improved land drainage: by providing an easier path for water to reach a main channel, flood peaks may be increased. However, the average catchment wetness is likely to be decreased by land drainage so that, provided that the rate of rainfall is less than the infiltration rate, a lower percentage of runoff will result.


development, demand and the production of water scarcity

The Thames region is home to nearly 12 million people, and is densely populated. Fourteen counties, fifty eight district councils, and thirty three local planning authorities in London lie wholly or partly within the region.

The Thames region already faces pressure on its existing water resources, with 55% of effective rainfall abstracted for use, and a geographical mismatch between demand (concentrated in the drier west of the basin) and supply. The majority of demand for water is domestic, and originates in major population centres -- such as London and surrounding satellite cities, Banbury, Guildford, Luton, Reading, Swindon, Oxford, and Watford. Rapidly growing urban centres, such as Swindon in the Upper Thames, have placed strain on local water supply in recent years.

The Thames region is predicted to be facing significant development pressures in the next two decades [17]. The Environment Agency has warned that: "water resource availability is a critical factor which can only be partially offset by reductions in leakage and water conservation measures. Proposed levels of development could raise serious problems for water resources in the medium to long-term" (Environment Agency 1998, 44) [18]. In this way, Local Authorities are now required "take water constraints into account when considering the location of new development, including the environmental impact of any new water resource development which may be required as a consequence" and to "require specific water conservation measures in new development" (SERPLAN 1998, 40) [19].

The limits to available water supply will be reached, if demand continues to grow at recent rates and no new major resource developments are initiated, within the next 20 years [18]. The growth in single-person households (which use more water per capita), changing consumer goods ownership patterns, and increased garden watering are critical factors in the growth in demand. Sustainability reductions to meet increasingly stringent environmental legislation (for the most part originating at the EU level), and an increasing incidence of pollution incidents (particularly affecting groundwater) will further reduce water availability. As demand increases, the margin between supply and demand (‘headroom’) will decrease gradually. Nonetheless, as the robust performance of water sources and lack of water restrictions demonstrated during the most recent drought episode in the Thames region (1995 — 1997), this increasing insecurity of water supply will not necessarily be evident to water consumers, unless the frequency and amplitude of extreme meteorological drought events, in line with some climate change scenarios, were to increase significantly.



1. NRA (1994) Future Water Resources in the Thames Region: A Strategy for Sustainable Management, Reading, National Rivers Authority

2. NRA (1995) Policy and Practice for the Protection of Groundwater: Regional Appendix, Thames Region, Reading, National Rivers Authority

3. EA (1998) Progress in Water Supply Planning: The Environment Agency's Review of Water Company Water Resource Plans. Bristol, Environment Agency

4. NRA (1995) Fact File: Upper Thames, Reading, National Rivers Authority. PLACE

5. NRA (1995b) Fact File: Middle Thames, Reading, National Rivers Authority. PLACE

6. NRA (1995c) Fact File: Lower Thames, Reading, National Rivers Authority. PLACE

7. NRA (1995d) Fact File: Tidal Thames, Reading, National Rivers Authority. PLACE

8. Jamieson, D. G. and N. J. Nicolson (1984) Water Resources of the Thames Basin: Quantitative and Qualitative Aspects. Journal of the Institution of Water Engineers and Scientists 38 (5), 379 - 391

9. Brown, A. (1992) Inland water quality and pollution. The UK Environment. A. Brown. London, HMSO: 87 - 105

10. IOH (1995) Hydrological Data United Kingdom: 1994 Yearbook, Wallingford, Oxon, Institute of Hydrology and British Geological Survey

11. Arnell, N. W., A. Jenkins, et al. (1994) The Implications of Climate Change for the National Rivers Authority, NRA Research and Development Report, 12. Bristol, NRA.

12. Herrington, P. (1996) Climate Change and the Demand for Water, London, Department of the Environment

13. DoE (1996) Review of the Potential Effects of Climate Change in the United Kingdom. HMSO, London

14. Crooks, S.M. (1994) Changing Flood Peak Levels on the River Thames, Proceedings of the Institute of Civil Engineers: Water, Maritime, and Energy 106, p. 267-279

15. Handmer, J.W., Penning-Rowsell, E.C, and Tapsell, S. (1998) Flooding in a warmer world: the view from Europe. In: Downing, et al (Eds) Climate, Change and Risk, London: Routledge: 125-161

16. EA (1998b) Middle Thames Fact File, Environment Agency - Thames Region

17. NRA (1995e) Thames 21 - A Planning Perspective and a Sustainable Strategy for the Thames Region, Reading, National Rivers Authority

18. EA (1998d) The Environment Agency's State of the Environment Report for Thames Region, Reading, Environment Agency - Thames Region

19. SERPLAN (1998) A Sustainable Development Strategy for the South East, London, The London and South East Regional Planning Conference.



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