Damage to the River Mekong Basin
Mekong is a river that runs across Southeast Asia and is considered as the tenth longest river in the world. It is approximately 4,900 km and covers an area of roughly 795,000 square km. the river runs across several countries, including China, Burma, Laos, and Vietnam.
Since the river flows through highly populated areas with intensive agricultural activities and water diversion practices, it has continuously undergone a shift in its hydrology especially when it flows through China.
For instance, China is currently embarking on a project in which it will construct dams out of the river, three of which have been completed, while 12 are on different stages. In Thailand, the Pak Mun dam is already complete, and in Cambodia, a reserve has been constructed on the Tonle Sap River, which flows into the Mekong.
These dam construction activities have had adverse effects on the hydrology of the river. The lower Mekong River has experienced a reduction in water levels over the years, and this reduction has been attributed to dam construction activities upstream.
For instance, the filling of the Manwan reservoir 1n 1992 caused a drastic reduction in the water level in the river (Walling, 2006). An assessment of the river at various stages showed that an interruption of the regular water flow, evidenced by an increase in sediment in Mekong’s bed.
Eve though some of these constructions are not undertaken on the main course of the river, the effect is still significant, for instance, studies show that construction on the Lankang River, the Mekong’s main stream, has caused a considerable reduction of water downstream (Lu and Siew, 2006).
Dam construction has increased the volume of sediments in the Mekong River. This is because a reduction in the flow of water effectively reduces the amount of water to transport the sediments downstream. Therefore, the sediments settle at the bottom of the river and reduces it depth.
Indeed, studies show that areas along the middle and latter points of the Mekong River have had a reduced amount of sediment flux, mainly attributed to the sedimentation of the Manwan dam. The sediments are also captured in the reservoirs and dams that are constructed on the river or its tributaries.
A reduction in sediment flow has had a huge effect on the hydrology and ecosystem of the Mekong, especially at the downstream sections (Kummu & Varis, 2007). Sediment flux leads to a low water depth and this has caused ferries to get stuck, smaller fish are now caught and the catch has dropped drastically while the Chiang Rai port on River Mekong is recording very low business.
Sediment flux along the Mekong River has mainly affected areas immediately downstream of the dams under construction or being in-filled. This quite different to some areas in which the flow has either increased or remained constant most probably as a result of alluvial storages within those areas.
Surprisingly, a decline in sediment flux also comes with some advantages, for example, it would enhance regulation of the flood cycle, hence lowering the frequency and degree of floods. However, areas that depend on floods to get nutrients will suffer consequently.
The Tonle Sap River and its ecosystem have been mostly affected by dam construction upstream (Kummu and Sarkulla, 2008). Dam constructions have caused a shift in the direction of flow of the Mekong River and this has led to a grave effect on the ecosystem.
Alterations in flow and a reduction of the volume of flow have affected Tonle Sap’s floodplain, and its forest, by altering the flood-pulse mechanism of Lake Tonle Sap. This has caused a gradual loss of the forest and other protected areas and this in turn affects the livelihoods of persons who live downstream and who depend on Tonle Sap’s natural resources.
Mitigation strategies to address damage to natural systems
The first mitigation measure to prevent damage to the downstream Mekong River is to regulate the construction of dams and reservoirs. To achieve this effort, the countries through which the river passes have formed a commission known as Mekong River Commission.
The commission has regularly blamed China for its disregard to the effort to stop construction of dams. Regulation of dam construction would ensure that water in the dam remains at levels that do not lead to sediment flux, nor does it lead to flooding.
Lu and Siew (2005) argue that rivers have a natural ability to “maintain an equilibrium despite alterations in their hydrologic regimes”, while this assertion may be true, it may not work in cases of extreme damage to river regimes. Therefore, a mitigation strategy must be put in place.
Such a strategy would involve dredging, where sediment are physically removed from the river bed so that the water can flow freely. While this is only a short-term solution, it will be useful while permanent methods, which may take a long time due to the involvement of many countries, are being sought.
References
Kummu, M., and Sarkkula, J. (2008). Impact of the Mekong River Alteration on the Tonle Sap Flood Pulse. Ambio., 37(3).
Kummu, M., and Varis, O. (2007). Sediment-related impacts due to upstream reservoir trapping, the Lower Mekong River. Geomorphology 85, 275 – 293.
Lu, X. X., and Siew, Y. (2006). Water discharge and sediment flux changes over the past decades in the Lower Mekong River: possible impacts of the Chinese dams. Hydrol. Earth Syst. Sci., 10, 181-195.
Lu, X. X., and Siew, Y. (2005). Water discharge and sediment flux changes over the past decades in the Lower Mekong River. Hydrol. Earth Syst. Sci. Discuss., 2, 2287-2325.
Walling, D. E. (2006). Human impact on land-ocean sediment transfer by the world’s rivers. Geomorphology 79, 192-216.