1 CATCHMENT MODELLING FOR CATCHMENT FLOOD MANAGEMENT PLANS DAVID RAMSBOTTOM, CEng MICE MCIWEM, DARREN LUMBROSO, CEng MICE MCIWEM and MARK DAVISON HR Wallingford Ltd Key Words: Catchment, Flood, Modelling Abstract Catchment Flood Management Plans (CFMPs) are being undertaken for all river catchments in England and Wales. Catchment modelling is required to predict the effect on flood risk of future land use change and climate change, and possible future flood management policies. A method of catchment modelling has been developed as part of the Modelling and Decision Support Framework (MDSF). This paper briefly describes the catchment modelling approach recommended for CFMPs and application to several catchments including the Thames upstream of Kingston. Issues arising from experience is using the approach are also discussed. INTRODUCTION A programme of Catchment Flood Management Plans (CFMPs) has been launched for England and Wales by the Environment Agency. CFMPs are intended to provide a “broad- brush assessment of risks, opportunities and constraints”, sufficient to identify policies for managing floods in a catchment together with possible measures to achieve these policies (Defra/Environment Agency 2002b). Preparation of CFMPs involves catchment modelling to identify the effects of possible future climate and other changes on flood risk, and to assess the effectiveness of flood management policies and measures. The selection of an appropriate level of modelling is a crucial part of the CFMP process, as it has a major impact on the scope of work and cost of a CFMP. A Modelling and Decision Support Framework (MDSF) has been developed to facilitate the production of CFMPs (Defra / Environment Agency 2002a). The MDSF includes software that uses results from catchment modelling to calculate the economic damages and social impacts of flooding under present day and future conditions. The MDSF also includes guidance on catchment modelling, contained in the ‘MDSF Procedures’. When the initial version of the MDSF was produced in December 2001, it was recognised that there were gaps in the guidance for catchment modelling. Additional research work was therefore carried out to fill these gaps and provide more specific guidance (Defra/Environment Agency 2003a). The improved guidance was included in an update of the MDSF Procedures (Defra/Environment Agency 2003b). This paper briefly describes:  The development of the catchment modelling approach recommended for CFMPs;  A summary of the approach;  Experience to date of catchment modelling for CFMPs;  Current issues. REQUIREMENTS OF CATCHMENT MODELLING A catchment model for a CFMP must be able to: