The Mekong basin is undergoing rapid development. Basin wide water infrastructure development, climate change and landuse change are causes for concern due to potential impacts on highly valued fisheries, agriculture, and natural ecosystems through changes in water, sediment and nutrient flows. In the Mekong floodplains, impacts of flood protection dykes, land subsidence, and sea level rise need to be better understood. The aim of this presentation is thus to i) assess the current level of changes through historical hydrological data analyses, ii) model (hydrological and hydraulic) future threats and their impacts, and iii) discuss potential adaptation and mitigation measures to reduce future impacts. Historical water levels of the Mekong were analyzed by comparing pre and post 1991 daily data of 6 stations along the Mekong mainstream from Chiang Sean, in northern Laos, to Stung Treng, in Cambodia, and the PreKdam station in the lower Mekong floodplain. The year 1991 marked a turning point in the rate of development in the basin. Observed changes in water level patterns along the Mekong were linked to temporal and spatial water resources development from 1960 to 2010. Variations in climate are important, but they were not observed to be the main causes of changes in key hydrological indicators related to ecosystem productivity. The development of mainstream dams in the upper Mekong basin in the post 1991 period resulted in a significant change of seasonal water levels, raise rates, fall rates, and the number of water level reversals observed in Chiang Sean. This effect diminishes downstream until it becomes negligible at the Mukdahan monitoring station, which represents a drainage area of over 50% of the total Mekong Basin. Further downstream at the Pakse station, changes in hydrological indicators post 1991 were observed to be significant again, which can be directly attributed to water resource development in the Chi and Mun River basins of Thailand. A reduction of 23% and 11% in the raising rate and fall rate, respectively, at the Tonle Sap provides clear evidence of a diminished flood pulse in the post 1991 period. Through subsequent modeling we infer how future changes could further impact water flows and livelihoods in the Mekong floodplains. Recent development of flood protection dykes, as well as sea level rise and land subsidence pose a major threat to the long term sustainability of the Mekong Delta. Future adaptation and mitigation strategies should include optimal operation of water infrastructure (hydropower, dykes, and irrigation systems) to reduce hydrological and sediment changes, reduction in groundwater pumping, water storage management, sea level rise protection infrastructure, land reclamation, enhancement of coastal and in-stream habitats and others. A single solution is not sufficient for this complex basin; multiple mitigation initiatives are necessary through transboundary communication and coordination. The analysis and methods, as well as the lessons learnt in this research can be translated to other river systems around the world undergoing rapid development and climatic threats.
Tom Cochrane is an academic and associate head of the Department of Civil and Natural Resources Engineering at the University of Canterbury in New Zealand. For the past 10 years he has led research on the interactions between infrastructure development, hydrology, and agriculture in the Mekong basin. He also conducts research in land and water resources conservation and urban stormwater monitoring and modelling. Tom obtained his PhD from Purdue University in 1999, worked as a consultant in South America for 5 years and joined the University of Canterbury in 2005.