The subject of water resources provided the greatest motivation for the growth in hydrological studies in the twentieth century. An expansion of hydrological measurements, especially in the second half of the twentieth century, was driven largely by needs for the evaluation of water resources, which initiated widespread and comprehensive study of the hydrological environment. In the UK, legislation for water dated from the Victorian era, when Acts of Parliament were passed to grant powers at a local level to provide water supply and sewerage for the rapidly expanding population centres. It was the Water Resources Act of 1963 that consolidated water resources management at a regional and national level, creating River Authorities responsible for enforcing the law in relation to water resources. The 1963 Act set the legal basis for regulation of abstractions and impoundment of water.
The establishment of hydrological measurement networks resulted from the legal requirement laid on the former river authorities to evaluate the water resources of their areas. Before the new gauging stations had time enough to produce the long-term information required by the planners, hydrologists had to devise techniques for making assessments from the limited data, which stimulated development of statistical methods and modelling techniques in hydrology, see Chapters 11-14. It will be seen that demand for reliable and safe public water supply is critical to the management of water resources, albeit placed in an environmental regulatory framework. Hydrological studies for water resources in the UK are often linked to balancing requirements for water supply with environmental considerations through mechanisms such as water resources management plans and abstraction strategies. It is only possible to cover some of the relevant techniques here. Detailed guidance on the subject of water supply, including hydrological analysis and water quality standards can be found in Twort et al. (2000) and other specialist texts.
The British Isles are often characterised as having a temperate, maritime climate, with annual average rainfall over England and Wales of 890 mm, reaching more than 2500 mm in hilly regions in the north and west. However, parts of the south and east of England have high population densities and relatively low annual rainfall of less then 200 mm. The 'water exploitation index' is the amount of freshwater resources abstracted as a proportion of effective rainfall. It is a useful summary measure of whether a region can be considered to be under 'water stress'. In the south-east of England the water exploitation index is greater than 20 per cent. Fig. 17.1 shows
how this compares to other parts of Europe. It can be seen that south-east England is anomalous compared with most other parts of northern and western Europe. Only in much drier countries is there greater water stress.
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