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River tributaries have a key role in the biophysical functioning of the Mekong Basin. Of particular attention 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 would alter the hydrology of the Tonle Sap 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 definite future development scenario (DF) 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 d-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 actually be exploited and that dams would be built even in locations where there is a high risk of ecological disruptions. 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. [ABSTRACT FROM AUTHOR]

The Mekong River supports unique biodiversity and provides food security for over 60 million people in the Indo-Burma region, yet potential changes to natural flow patterns from hydropower development are a major risk to the well-being of this system. Of particular concern is the ongoing and future development of 42 dams in the transboundary Srepok, Sesan and Sekong (3S) basin, which contributes up to 20% of the Mekong's annual flows and provides critical ecosystem services to the downstream Tonle Sap Lake and the Mekong Delta. To assess the magnitude of potential changes, daily flows were simulated over 20 years using the HEC ResSim and SWAT models for a range of dam operations and development scenarios. A 63% increase in dry season flows and a 22% decrease in wet season flows at the outlet of the 3S basin could result from the potential development of new dams in the main 3S rivers under an operation scheme to maximize electricity production. Water-level changes in the Mekong River from this scenario are comparable with changes induced by the current development of Chinese dams in the Upper Mekong Basin and are significantly higher than potential flow changes from the proposed 11 mainstream dams in the Lower Mekong Basin. Dams on the upper sub-tributaries of the 3S basin have very little effect on seasonal flow regimes because most of those projects are run-of-the-river dams and have small reservoir storages. The effects on hourly flow changes resulting from intra-daily reservoir operations, sediment movement, water quality, and ecology require further study. Strategic site selection and coordinated reservoir operations among countries are necessary to achieve an acceptable level of development in the basin and to mitigate negative effects in seasonal flow patterns, which sustain downstream ecosystem productivity and livelihoods. [ABSTRACT FROM AUTHOR]

The article focuses on the Mekong River which provides renewable energy and food security to the countries including China, Vietnam and Cambodia. Also includes the threat to fisheries and agriculture because of hydropower development; food, energy, and water challenges being faced by global tropical rivers; and control of impending hydropower operations to improve fisheries yield.