Flood-plain mapping of the River Leam and River Itchen

As part of the requirements of s. 105 of the Water Resources Act 1991, the Environment Agency is producing flood-plain maps of all major rivers. Where no historic data are available for a large flood event, mathematical model s are used to simulate 100-year design flood flow events, which allows the definition of flood-prone areas. These maps, together with a database of th e water levels and flows, will form part of a national Flood Plain Informat ion System. This paper describes the development and generation of flood-plain maps for the Rivers Leam and Itchen in Warwickshire. The data collection and review of topographic and hydrometric data are outlined. Procedures for combining information from gauged data, historical flood data and methods based on c atchment characteristics form the basis for estimating design input flows t o hydraulic models. Modelling principles and data requirements of two diffe rent hydraulic models, used to estimate peak water levels of design return period, are described.