Abstract
Abstract. River tributaries have a key role in the biophysical functioning of the Mekong Basin. Of particular interest are the Sesan, Srepok, and Sekong (3S) rivers, which contribute nearly a quarter of the total Mekong discharge. Forty two dams are proposed in the 3S, and once completed they will exceed the active storage of China's large dam cascade in the Upper Mekong. Given their proximity to the Lower Mekong floodplains, the 3S dams could alter the flood-pulse hydrology driving the productivity of downstream ecosystems. Therefore, the main objective of this study was to quantify how hydropower development in the 3S, together with definite future (DF) plans for infrastructure development through the basin, would alter the hydrology of the Tonle Sap's Floodplain, the largest wetland in the Mekong and home to one of the most productive inland fisheries in the world. We coupled results from four numerical models representing the basin's surface hydrology, water resources development, and floodplain hydrodynamics. The scale of alterations caused by hydropower in the 3S was compared with the basin's DF scenario driven by the Upper Mekong dam cascade. The DF or the 3S development scenarios could independently increase Tonle Sap's 30-day minimum water levels by 30 ± 5 cm and decrease annual water level fall rates by 0.30 ± 0.05 cm day−1. When analyzed together (DF + 3S), these scenarios are likely to eliminate all baseline conditions (1986–2000) of extreme low water levels, a particularly important component of Tonle Sap's environmental flows. Given the ongoing trends and large economic incentives in the hydropower business in the region, there is a high possibility that most of the 3S hydropower potential will be exploited and that dams will be built even in locations where there is a high risk of ecological disruption. Hence, retrofitting current designs and operations to promote sustainable hydropower practices that optimize multiple river services – rather than just maximize hydropower generation – appear to be the most feasible alternative to mitigate hydropower-related disruptions in the Mekong.
Highlights
More than half of the world’s greatest rivers have been altered by dams (Nilsson et al, 2005) and there is worldwide evidence showing that hydropower development causes significant hydrological and ecological disruptions to downstream freshwater ecosystems (Poff and Zimmermann, 2010)
We have taken a step further and shown that the corresponding hydrological alterations from the 3S hydropower projects are as large; perhaps more importantly, we have demonstrated that the cumulative effect of development in the Upper Mekong and the 3S will cause significant disruption to the inundation patterns of the Lower Mekong floodplains, in particular through an increase in dry season water levels as well as a reduction in water level rise and fall rates
This paper presented a study in which hydrological modeling and assessment tools were used to provide evidence of the expected hydrological alterations that hydropower development in the Lower Mekong tributaries could bring to the Tonle Sap
Summary
More than half of the world’s greatest rivers have been altered by dams (Nilsson et al, 2005) and there is worldwide evidence showing that hydropower development causes significant hydrological and ecological disruptions to downstream freshwater ecosystems (Poff and Zimmermann, 2010). Arias et al.: Dams on Mekong tributaries as contributors of alterations to the Tonle Sap Floodplain stakeholders differ from those downstream. Such is the case of the Mekong, a transboundary basin with historically low levels of hydrological regulation (i.e., the fraction of the annual water discharge that can be stored in reservoirs) comparable to other large tropical basins such as the Amazon and the Congo (Lehner et al, 2011; Nilsson et al, 2005). Aggressive plans for multiple large hydropower schemes throughout the Mekong Basin for economic development are expected to bring significant disruptions to the hydrological regime (Lauri et al, 2012; Piman et al, 2013b), compromising the geomorphology (Kummu et al, 2010; Walling, 2009), fish ecology (Ziv et al, 2012), and productivity of the downstream floodplain ecosystems (Arias et al, 2014) that sustain the food security of millions of people
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
