River modelling for flood risk map prediction

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Date
2009
Authors
Alaghmand, Sina
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Abstract
The research illustrates an importance of river flood in urban areas which cause lost of lives and properties damages. Knowledge on the river basin response to rainfall events of runoff is vital in engineering practices for urban planning and development. Flood hazard map prediction is a combination of hydrological modelling, hydraulic modelling and river flood visualization using GIS. The case study of this research is Sungai Kayu Ara located in Damansara, Kuala Lumpur. A total of 36 scenarios are identified in order to assess the effects of rainfall magnitude (20 year, 50 year and 100 year ARI) and duration (60, 120, 180 and 360 minutes) for existing, intermediate and ultimate development conditions. The results of hydrological model simulation indicated that, an increase in the rainfall magnitude leads to increase of runoff volume and peak discharge while increase of rainfall event duration increases the runoff volume but decreases the runoff peak discharge. Furthermore, an ultimate river basin development conditions (90% imperviousness) generate higher runoff volume and peak discharge in comparison with existing and intermediate development conditions. The river flood hazard maps are generated based on water depth, flow velocity and combination of water depth and flow velocity. These maps showed that the impact of water depth is more considerable than flow velocity during river flood. Hence, hazard attributed to water depth is more significant in comparison with flow velocity. River flood hazard maps are the base of the river flood risk prediction. River flood risk maps are considered as the function of river flood hazard, vulnerability and exposure. In this case, land-use type, main road accessibility and debris flow are involved to reflect the terms vulnerability and exposure in river flood risk map prediction. These four elements are provided as GIS raster layers in which all pixels indicate the severity value of each element. The generated river flood risk map is the result of combination of four main elements, river flood hazard, land-use type, main road accessibility and debris flow. The suggested method for river flood risk map prediction recommends four classes of severity for river flood consists of, low, medium, high and extreme. The established flood risk prediction map has shown that the river flood hazard, debris flow hazard, land-use type and main road accessibility have significant impact and able to facilitate the planning and management of river flooding in urban areas. The variation of predicted river flood risk pattern is a function of river flood hazard and debris flow hazard patterns; as the distribution of hazards produced by land-use type and main road accessibility is uniform.
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Master
Keywords
River modelling , Flood risk map
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