12The Mekong Delta is one of the largest and most intensively used estuaries in the world. Each 13 year it witnesses widespread flooding which is both the basis of the livelihood for more than 14 17 Million people but also the major hazard. Therefore, a thorough understanding of the 15 hydrologic and hydraulic features is urgently required for various planning purposes. interference which is governed by flood protection levels, cropping patterns and communal 27 water management. In addition, we examine the tidal influence on the inundation in various 28 parts of the Delta, since it is expected that climate change induced sea level rise will increase 29 the tidal contribution to floodplain inundation. 30 2

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The Cu Chi irrigation system in Vietnam forms part of the Dau Tieng reservoir system in the Dong Nai basin. Water competition in this system is intensifying as a result of increasing urban and environmental demand. System operation modelling using the Irrigation Main System OPeration (IMSOP) model was applied to the Cu Chi irrigation system, Vietnam, to improve its operational performance. The operation improvement process involved the comparison of supply and demand during two years, 2001 and 2002, revealing that the system's operation was carried out without consideration of the crop water demand and proper canal regulation. The retrospective operational analysis revealed a substantial amount of oversupply and inequity of distribution. Two new operation strategies were selected after a simulation analysis and evaluated in the field. The new scenarios showed a more equitable distribution of water in the system. The average pre-intervention supply-demand ratio which ranged from 1.68 to 2.51 was reduced to 1.20 for continuous flow and 1.17 for rotational operation. A comprehensive analysis of water reallocation to Ho Chi Minh City for urban and industrial purposes and its effect on the security of supply on the Cu Chi system was also undertaken. Copyright # 2004 John Wiley & Sons, Ltd.

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