The 2009 Flood Risk Regulations and the 2010 Floods and Water Management Act now require all local authorities in England and Wales to “develop, maintain, apply and monitor a strategy for local flood risk management in its area”, and where flooding occurs, to “investigate what should be done and by who.” This necessitates the need for an integrated approach to river, sewer and overland flow modeling for the purpose of assessment and mitigation of flood risk. This paper presents an explicit integrated catchment modeling methodology for use in assessing the environmental impact from urban catchments on the receiving waters and planning wet weather discharges in urban drainage systems. The method consists essentially of linking one dimensional (1-D) hydrodynamic simulation of flows in rivers, open channels and pipe networks with two dimensional (2-D) hydrodynamic simulation of surface flooding in the urban environment and river floodplain. The resulting model provides a comprehensive analytical framework for simultaneously modeling below ground and above ground elements of catchments to accurately represent all flow paths and improve understanding of the processes occurring in the holistic environment. The model can take into account interactions of natural-manmade environments and effectively simulate the water quality impact of polluting runoff and effluent from urban areas. Such capabilities will greatly enhance the ability of water utilities to conceive and evaluate sound and reliable urban catchment strategies such as storm sewer separation, active real-time control and provision of adequate additional storage. The versatility and wide range of applications of the model are discussed and conclusions are stated. Enhancement of urban catchment planning, management and operation is a principal benefit of the proposed methodology.