The impact of building coverage in the metropolitan area on the flow calculation
Date Issued
2012
Date
2012
Author(s)
Wang, Yen-Hsiang
Abstract
Due to the special hydrographic and physiographic conditions in Taiwan, whenever a typhoon or rainstorm event comes, flooding is likely to occur in the middle and lower reaches of the plains. Noteworthily, the loss of lives and property caused by flooding will be the most considerable one in the metropolitan area. However, the modern tall building stands in great numbers in metropolitan areas, which leads to the increase of impervious area as well as the decline of water storage area. Furthermore, a large number of intensive building changes the original land flow conditions, resulting in a beam shrinking flow and the additional form drag phenomenon which makes the flooding phenomenon more serious.
The main purpose of this research is to find out the correlation of building coverage and the Manning ’s n through flume model experiment. To probe into this issue, the Manning ’s n changes is further divided into those caused by surface impedance and those caused by the building impedance. Thus, the building coverage can be added to the general computing grid and reflects the flooding situation with building. Afterwards, a further calculation can be carried out to have in hand the volume conversion situations when flooding depth reaches a certain height and when the water flows into the building so as to reflect the actual situation when the building is flooded.
The model will be applied to the simulation district of Taichung City for an actual case simulation. Using the rainfall data of Typhoon Kalmaegi in 2008, we calibrate the surface roughness of the model in accordance with building coverage from the comparision of the flooding scope and flooding depth. The results show that we can seriously neglect the water blocking effect of the building before the adjustment of surface roughness. Therefore, it might be more pertinent to take into consideration of the building factor in the flooded mode and adjust the surface roughness according to the ratio of the building coverage in the grid, when the two-dimensional model is used to undertake the flow simulation of the metropolitan areas. In this way, we can make the flooding situation more in line with the actual situation.
Subjects
Inundation model
building coverage ratio
Type
thesis
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