Reed, D.W., Field, E.K. 1992. Reservoir flood estimation: another look. Report No. 114, IH, Wallingford, 96 pp.
The assessment of flood risk is a vital element in the safe design, maintenance and operation of impounding reservoirs. Since the introduction of reservoir safety legislation in 1930, strengthened by the 1975 Reservoirs Act, the record of reservoir flood safety in the UK has been excellent by world standards. Nevertheless, the need remains for adequate provision to discharge floods safely at some 2400 large impounding reservoirs, many of them old and often sited above the communities which they serve.
This report summarises a study funded by the Department of the Environment's Reservoir Safety Commission under DoE Contract No. PECD7/7/135. It takes another look at reservoir flood estimation. Reference is made to developments elsewhere, but the review is primarily concerned with UK methods and experience. After identifying the procedures currently recommended, the report explores aspects of flood estimation and research which are particularly relevant to reservoir flood safety appraisals. Extensive comparisons of design floods are presented for 15 reservoired catchments.
Special topics are explored: the sensitivity of reservoir flood estimates to the precise storm duration assumed, and comparisons between 'summer' and 'winter' values of the Probable Maximum Flood (PMF) and between 0.5PMF and 10,000-year flood estimates. New algorithms are presented for 'level-pool' flood routing, with detailed examples. Controversial areas are explored, including snowmelt allowances in PMF estimation, and the incorporation of local data into reservoir design floods.
The report concludes with a selective review of procedures and developments elsewhere in the world, highlighting some of the fundamental choices in reservoir flood estimation which underlie UK practice. More than 150 references are cited, almost all of them post-dating the Flood Studies Report of 1975.