On the Importance of Suburban Catchments to the Discharge Behaviour of Large Drainage Networks

Design, maintenance and management of large urban drainage systems are commonly based on hydrodynamic modelling of the system, requiring data of the system and its connected areas. Operators of urban drainage systems in large cities are responsible not only to deal with waste- and storm water generated within the city boundaries but furthermore also for the runoff generated in the surrounding suburban and rural areas. Lack of information regarding the details of the drainage system in these surrounding areas is a frequent problem. This paper presents a simple methodology to identify the most relevant areas and to give information how many and which surrounding communities are to be assessed in detail. It is shown that estimating the suburban connected area is of minor importance when considering submerge and overflow frequencies within the city boundaries. Furthermore it is estimated that for most of the investigated indicators only few relevant surrounding communities need to be assessed in detail.