Urban water management: Spatial assessment of the urban water balance

Abstract

For fast emerging Asian megacities, knowledge of water resource conditions is indispensable for sustainable water balance management and planning. Urbanisation results in the sealing of surfaces to different degrees in relation to the urban densities and structures developed and ultimately to an alteration of the urban hydrograph. In recent decades urban flooding in Ho Chi Minh City has become one of the most pressing issues. To support the Ho Chi Minh City’s planning authorities, within the frame of this the research project TP. Ho Chi Minh, the rainfall-runoff regime of the southern Vietnamese metropolis of Ho Chi Minh City was investigated. On the basis of high resolution digital databases as well with a previously generated urban structure type map, a German water balance model ABIMO was used to calculate the long-term annual means of individual water balance components for the entire administrative area of the city. Current conditions and further time-series of future urban development scenarios as set out in the draft land use plan up to the year 2020/25 over static climate conditions were modelled. The results were mapped for each of the individual 16,282 land-use blocks of the city’s official land use plan and construed to planning recommendations. The results showed that for the current conditions from a total annual precipitation input of 1573 mm, 117 mm or approximately 7 % is unable to infiltrate or evaporate and converts into surface run-off. Evidence, that urbanization is one of the main cause of increased flooding, could be given by the finding that currently 212 million m3 and based on the simulation for the year 2020/2025 overland flow of 586 million m3 will occur. Finally on the basis of modelled results, a planning recommendation map was compiled displaying zones as planning priorities, targets and measures.