This guidance aims to provide best practice advice for the design and management of urban sewerage and drainage systems to reduce the impacts that arise when flows occur that exceed their capacity. It includes information on the effective design of both underground systems and overland flood conveyance. It also provides advice on risk assessment procedures and planning to reduce the impacts that extreme events may have on people and property within the surrounding area. The broad objective of the guidance is to improve engineers, planners and designers appreciation of the risks associated with urban drainage systems and their understanding of how these risks may be mitigated. It provides guidance so that systems can be designed to safely and sustainably accommodate periods when the design capacity of drainage systems are exceeded during extreme events. The guidance will be relevant to areas drained by piped systems or SUDS.