Dams on Mekong tributaries as significant contributors of hydrological alterations to the Tonle Sap Floodplain in Cambodia

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)(1987)(1988)(1989)(1990)(1991)(1992)(1993)(1994)(1995)(1996)(1997)(1998)(1999)(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.

Model-Based Assessment of Water, Food, and Energy Trade-Offs in a Cascade of Multipurpose Reservoirs: Case Study of the Sesan Tributary of the Mekong River

“…The future climate change projections of Ty et al (2012) are in line with projected changes in the Mekong Basin . In addition, the impacts of hydropower development in the 3S Rivers on the Tonle Sap Lake in Cambodia have been assessed by Arias et al (2014b). Kummu et al (2010) estimated the sediment trapping efficiencies of existing and planned hydropower reservoirs in the Mekong Basin.…”

Large-scale impacts of hydropower development on the Mompós Depression wetlands, Colombia

“…CC BY 4.0 License. dispersion, and colonization of plants; triggers for fish migration; and access to soil moisture, among many others (Arias et al, 2014;Poff & Zimmerman, 2010).…”

Longitudinal gradient in limnological variables in the Upper Paraná River: a brief description and the importance of undammed tributaries

“…The studied region suffers great influence of upstream reservoirs, especially from Porto Primavera dam (Montanher & Souza Filho, 2015), that retains more than 70% of the Paraná river total phosphorous (Roberto et al, 2009). Decreases in nutrient concentrations caused by dams barring the river course are widespread in the world and reported in several studies (Kummu & Varis, 2007;Fu et al, 2008;Ouyang et al, 2011;Arias et al, 2014). The low values of total phosphorous and nitrogen and the high values of Secchi disk depth observed in those sites closest to Porto Primavera dam are in accordance to the general trend observed worldwide, indicating that Porto Primavera dam is indeed acting as a sink of environmental nutrients.…”