Enhancing sustainability of the Transboundary Cambodia - Mekong River Delta Aquifer

The lower section of the Mekong River Basin is underlain by a major transboundary aquifer system shared by Cambodia and Viet Nam: The Cambodia – Mekong River Delta Aquifer[1]1. This transboundary aquifer system (TBA) connects two ecosystems of global environmental significance and socio-economic importance: the i) Tonle Sap area and the ii) Mekong Delta, and includes some major urban areas, including Phnom Penh and Ho Chi Minh. The whole area is approximately 200,000 km2 with about 63% lying within Cambodian territory. Tonle Sap, the largest lake in the Peninsular Indochina, is hydraulically connected to the Mekong River and serves as a natural regulating reservoir ensuring adequate groundwater recharge to the aquifer. One key hydrogeological characteristic of the aquifer system is that the upstream section in Cambodia has one single alluvial aquifer overlying older ‘hard rock’ formations, while in the delta region, in Viet Nam, at least eight alluvial aquifers can be distinguished on the basis of depositional sequences ranging in age from Holocene to Middle Miocene (approx. 15 million years), and up to 800m thick.

The groundwater resources in this TBA have a considerable impact on human livelihoods and socio-economic development. Groundwater is critical for rice production and makes a substantial contribution to the national GDP of Viet Nam, and; supports the agricultural sector in Cambodia, accounting for half of the country’s GDP and employing 80–85% of its’ labor force. For these reasons, the aquifer is heavily exploited for irrigation and water supply. The annual groundwater extraction rate throughout the TBA is estimated to be about 800–900 million m3/year.

The diverse ecosystems of the region are exceptionally productive, as are the benefits derived from them by its inhabitants. The integrity of ecosystem services is critical both in terms of biodiversity and of the sustainability of a range of natural resources and products available to both urban and rural populations. The effects of surface and groundwater interactions nourish large tracts of forests and wetlands, which produce building materials, medicines and food, and provide habitats to thousands of species of plants and animals. Groundwater naturally interacts with areas of low-lying land where permanent wetlands tend to develop. These wetlands provide habitat for fish breeding, buffer flood events by absorbing huge quantities of excess water, and offer natural water cleansing functions. In addition, groundwater sustains wetlands during the dry season: when groundwater levels drop below the historic norms, wetlands can dry out.

The sustainability of water resources and the health of the delta and Tonle Sap ecosystems cannot be achieved without a proper and shared understanding of the regional groundwater flow regimes, especially with regard to the up-gradient recharge zones within the Cambodian territory.

The establishment of cooperative management frameworks for this major transboundary aquifer embracing the whole Mekong delta and extending upstream in Cambodia, is of critical importance because of the region’s high dependence on water resources, and vulnerability to climate-related hazards (floods and droughts, sea level rise).

So far, two major barriers have hindered the implementation of cooperative groundwater resources management strategies and plans: i) the different levels of understanding that the two countries have of the TBA system, and; ii)the differences in groundwater management policies in Cambodia and Viet Nam that increase the difficulty of reaching a bilateral agreement for sustainable TBA development.

Project Objective

To strengthen environmental sustainability and water security in the Lower Mekong Basin by focusing, for the first time, on improved governance and sustainable utilization of the Cambodia-Mekong River Delta Transboundary Aquifer.

Budget

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