Abstract
AbstractIntense rainfall in urban areas can often generate severe flood impacts. Consequently, it is crucial to design systems to minimize potential flood damages. Traditional, simple design of urban drainage systems assumes agreement between rainfall return period and its consequent flood return period; however, this does not always apply. Hydraulic infrastructures found in urban drainage systems can increase system heterogeneity and perturb the impact of severe rainfall response. In this study, a surface flood return period assessment was carried out at Lystrup (Denmark), which has received the impact of flooding in recent years. A 35 years' rainfall dataset together with a coupled 1D/2D surface and network model was used to analyse and assess flood return period response. Results show an ambiguous relation between rainfall and flood return periods indicating that linear rainfall–runoff relationships will, for the analysed case study, be insufficient for flood estimation. Simulation-based mapping of return periods for flood area and volume has been suggested, and moreover, a novel approach has been developed to map local flood response time and relate this to rainfall characteristics. This approach allows to carefully analyse rainfall impacts and flooding response for a correct flood return period assessment in urban areas.
Highlights
Urban drainage systems are most often designed with a specific return period or frequency of exceeding the maximum capacity
Full 1D/2D simulations of the 35 selected rainfall events have been performed and results analysed with special focus on the observed flood area and flood volume
Statistics and uncertainties derived from rainfall measurements or estimates, as well as the ones derived from urban drainage system development and modelling, can have a large impact on any analysis performed over complex urban drainage systems, especially if the assessment is focused on flooding, they should be a subject to consider in further studies (Deletic et al )
Summary
Urban drainage systems are most often designed with a specific return period or frequency of exceeding the maximum capacity. According to the European Standard DS/EN ( ): Drain and Sewer systems outside buildings, simple design methods for drainage systems can be based on the design storm frequency for surcharging of the systems For residential areas, this is, for example, recommended to be 1 in 2 years (i.e., a return period of 2 years). The design rainfall, that a specific part of the system should comply with for a specified return period, is defined by estimating the maximum rainfall intensity corresponding to the most critical rainfall duration of a point in question, e.g., following the Rational Method (Kuichling ) This assumes steady flow conditions and a linear relations between rainfall intensity and design flow at a specific point of the system, the contributing area being its gradient. The design flow can be used in simple systems to determine pipe dimensions under the assumption of uniform flow conditions, i.e., that backwater effects, pressurized pipes, etc. must not occur
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