Flood modeling and mitigation measures in an urban environment – a Case Study, Victoria, Australia

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Flooding on urban basins is intensifying due to rapid urbanization. Flooding primarily occurs because of drainage congestion of inland flow and/or over bank flow of rivers during severe rainfall events. Rapid urbanization is causing a major change in rainfall-runoff phenomenon and the drainage system as well. The overland flow pattern is becoming complex due to huge structural development, and therefore, the correct prediction of surface runoff is becoming a challenging issue.

The traditional storm water modeling approach, mainly for 1d pipe-network, is able to simulate the drainage system correctly until there is no overflow from the network inlet. When such overflows exist due to insufficient drainage capacity, it is difficult to produce the actual flooding condition using this traditional one-phase simulation technique.

Alternatively, by giving some extra effort the two-phase modeling (duel drainage) technique can be employed where the street-network is simulated as open channel to drain the water overflowed from the storm water pipe-network, and a better representation of flooding scenario can be obtained, if the flood extents do not expand beyond the streets. However, unfortunately for the larger events (100yr and PMF) in most cases the flood extents expand to private properties, where the duel drainage approach is unable to produce correct flooding scenario.

Therefore, the 1d/2d integrated flood simulation model, which is capable of incorporating all the drainage elements (flow paths) and their interactions properly, is necessary for an accurate prediction of urban flooding. This paper demonstrates the 1d/2d integrated modeling approach in an urban catchment. xpswmm and xp2D (xpswmm-2D) mathematical modeling software, which is one of the most widely used models designed to simulate urban storm water runoff, has been used to perform a simultaneous and integrated simulation of all drainage elements along with the 2d overland flood modeling in order to get a correct delineation of the flood extents for minor (10yr) and major (100yr) events.

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