Water resource management in the USA: a case study of large dams

The construction of large dams in the USA reveals a rapid growth in activity in the post-Second World War period, with the largest number of dams being inaugurated in the mid-1960s. Texas, with 823 dams, is the state with the largest number, followed in turn by California, Oklahoma, Pennsylvania and Colorado. At the other extreme some states have fewer than a dozen dams. Although there are large variations in the number of dams between states nearly all of them record peak constructional activity between the late 1950s and early 1970s. Surprisingly, most dams have relatively small reservoirs with about 70 per cent of the total having capacities of less than 10⁶ m³. Over two-thirds of all dams have been constructed with a single aim in view, with flood control being the most important reason. Only 1.5 per cent of all dams are utilized for four or more purposes. The objectives behind dam construction reveal changes since the 19th century. In the early years of the 20th century irrigation, hydro-electric power generation and water supply were the most important reasons for dam construction, whereas in the post-1950 period flood control stands out as the dominant activity. Changing technology, the introduction of specific legislation and changing attitudes to the environment have been the major influences on dam-building activity over the period studied.