Coupling SWAT with land cover and hydropower models for sustainable development in the Mekong Basin Mauricio E. Arias 1 Tom A. Cochrane 1, Thanapon Piman 1,2, Ornanorg Vonnarart 2, Thomas B. Wild 3, Daniel P. Loucks 3 1 Department of Civil and Natural Resources Engineering, University of Canterbury, New Zealand 2 Mekong River Commission 3 Department of Civil and Environmental Engineering, Cornell University, USA
Outline 1. Overview of the Mekong and the 3S 2. Modeling approach 3. Methodological challenges and solutions 4. Results a. Land cover change b. Baseline river flows and sediment loads c. Deforestation effects on sediment loads d. Hydropower alterations and sustainable alternatives
The Mekong: context & challenges Largest transboundary river in Southeast Asia Basin area:795,000 km 2 River length: 4,200 km Discharge : 14,500 m 3 /s Livelihoods/ecosystems adapted to unregulated hydrological cycle Biodiversity hotspot Mekong challenges Hydropower Irrigation Land use change Changing climate
Case study: Sekong, Sesan, and Srepok Rivers Largest tributary contribution to the Mekong River (17-20%) Basin area: 78,650 km 2 Hydropower development and deforestation are accelerating A transboundary river shared between Lao PDR, Cambodia and Vietnam Closest tributary to floodplain and delta Important contribution of aquatic biodiversity and ecosystem services: fish, habitats, and migration routes 2
Maximize Hydropower Benefits?? Maximize Basin Benefits
Land cover change Dinamica Modeling approach Weight of Evidence / cellular automata 250-m grid cells Forest cover maps Surface hydrology and erosion SWAT Curve number / USLE 2,282 hydrological response units Daily water flows and sediment loads Dam operations and reservoir water routing HEC-ResSim 1-D river hydraulics 41 reservoirs/106 river reaches Daily regulated river flows Reservoir sediment trapping and routing SedSim Daily mass balance 41 reservoirs/106 river reaches Daily dam trapping and sediment loads
Methodological challenges and solutions 1. Inconsistent historical land cover maps in the region Solution: Use MODIS forest cover product 2. Lack of sediment data at 3S outlet Solution: approximate load based on a sediment mass balance upstream and downstream on the Mekong 3. Unavailable reservoir operation rules Solution: Use two different sets of operation 1. Full level/ Run-of-River 2. Seasonal fluctuation/optimize reservoir storage
Land Cover Change 49 % forest 43 40 31 % forest
Annual sediment yield (10 6 tons) Mean annual water discharge (m3/s) Sediment Yields 20 18 16 14 12 10 8 6 4 2 Sediment yield Water discharge 0 1985 1987 1989 1991 1993 1995 1997 1999 2001 2003 2005 2007 Year 4500 4000 3500 3000 2500 2000 1500 1000 500 0
Land Cover Change Effects on 7 Sediments Sediment load, million tons 6 5 4 3 2 1 0-1 Recent past ±1 SD Recent past ±1 SD Recent past (2003 LULC) Projected (2040 LULC) Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Hydropower Effects on River Flows
Hydropower Effects on Sediments From Wild and Loucks (2014). Water Resources Research
1-Jan 1-Feb 1-Mar 1-Apr 1-Jun 1-Jul 1-Aug 1-Sep 1-Oct 1-Nov 1-Dec 1- Flow m 3 /s Energy (GWh/day) Sustainable Hydropower Alternatives: Environmental Flows Downstream water flows Energy output 8,000 7,000 Outlet of the 3S basin 140 120 120 6,000 100 5,000 4,000 3,000 2,000 1,000 0 Baseline scenario (no dams) Ecological flows Maximize energy 80 60 40 20 0 Maximize energy 59 Maintain ecological flows
Conclusions Forest cover expected to decrease from 50 to 31% by 2040 Large temporal and spatial variability in sediment loads Construction of all dams would increase dry flows by 63% and decrease wet season flows by 22% Dams could trap 40-80% of annual sediment load Mitigation strategies: Catchment protection through Payment for Ecosystems Services Establishment of ecological flow criteria Sediment release mechanisms
Acknowledgments Funding: MacArthur Foundation, Critical Ecosystem Partnership Fund Regional partners: Conservation International Collaborators: Aalto University, EIA Ltd Finland, University of Washington, National Heritage Institute EVERYONE HERE!
SWAT water flow calibration/validation Calibration period (1985-2000) Validation period (2001-2005) NS Vol ratio NS Volume ratio Monitoring Mean annual coefficient of (computed coefficient of (computed station River flow efficiency /observed) efficiency /observed) Kratie Mekong 13040 0.97 1.00 0.96 0.99 Stung Treng Mekong 12548 0.97 1.01 0.96 1.00 Lumphat Srepok 740 0.60 0.94 0.59 1.16 Attapeu Sekong 426 0.54 1.01 0.64 0.95 Bandon Srepok 278 0.64 1.03 0.53 1.12 Cau 14 Srepok 250 0.63 0.99 - - Trung Nghai Sesan 132 0.47 1.00 - - Kontum Sesan 96 0.41 1.01 0.42 1.21
Sediment load calibration R 2 = 0.46 NS = 0.37 R 2 = 0.54 NS = 0.46 R 2 = 0.52 NS = 0.35 R 2 = 0.47 NS = 0.43
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