During the last few years, conflicts between agriculture atid aquaculture have been an important issue in the Bac Lieu province, Mekong Delta. Vietnam. A large area of rice production has been converted to shrimp or .shrimp-rice hased production systems that require the intake of saline water into fresh water zones that have been used for agriculture. To manage this conflict, the provincial authorities have reviewed land use plans und ideniitied a hufter zone with a mixed land use system of shrimp-rice (rice in the rainy season and shrimp in the dry season when sluices are opened). Under the CPWF (Challenge Program on Waier and Food) Project No. 25. role playing games (RPGs) were applied for analyzing the land and water management strategy of farmers in the buffer zone. The RPGs organized in three villages (Phong Thanh, Ninh Thanh Loi and Vinh Loc) indicate that due to much higher revenue eatned from shrimp compared with rice, farmers are attempting numerous techniques to prolong the duration lil saline water in their fields for shrimp cultivation. This strategy makes the growing of a subsequent rice crop impossible even in the rainy season, thus requiring harmonization of water management at different levels (farm ami canal systems). The results from these RPGs also indicate the need for fuither research on cultivation techniques for the shrimp-rice systems and on participatory methods to achieve better understanding of farmers" decisions.

Agricultural production in the coastal wetlands of Asia is often hindered by salinity intrusion caused by tidal fluctuation. This paper reports changes in environmental and socio-economic conditions that followed the phased construction and operation of sluices for controlling seawater intrusion from 1994 -2000 in a coastal area of the Mekong River Delta, Vietnam. Canal water salinity decreased rapidly upstream of sluices, allowing rice cropping intensification and increased rice production in the eastern part of the study area. However, the livelihoods of farmers in the western part were adversely affected due to cessation of supply of brackish water that was needed for brackish-water shrimp farming, while the acid sulphate soils present there posed problems for rice cultivation. The poor farmers and landless people suffered more because the fishery resource that they depended on declined sharply due to reduced salinity and increased acidity in the canal water. The findings confirmed that the environment and resource use in the coastal lands are very sensitive to external intervention. A clear understanding of the socio-economic and environmental impacts of salinity control measures in coastal areas can help planning to enhance farmers' incomes while minimizing negative environmental impacts. Land-use policy formulation, planning and management should adopt a more holistic approach, taking into account the interests of all resource users, especially the poor, instead of focusing on any particular sector.

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By comparing the successful story of a hydrodynamic model (based on its contribution to policy changes, management options and livelihood improvement) with other modelling cases in the Mekong River Delta, five success factors are identified. These are (1) simulated phenomena relevant to and understandable by policy makers; (2) response to the needs of policy setting; (3) developed and handled by national modellers with direct links to the policy process; (4) availability of input data; and (5) long application history. These success factors provide higher opportunities for engaging modelling activities with policy setting