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Impacts of landuse change on sediment transport in the yali reservoir catchment
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Impacts of landuse change on sediment transport in the yali reservoir catchment

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3rd Mekong Forum on Water, Food & Energy 2013. Presentation from Session 9: Managing the impacts of dams across cascades.

3rd Mekong Forum on Water, Food & Energy 2013. Presentation from Session 9: Managing the impacts of dams across cascades.

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  • 1.65 1.38 0.273.75 3.13 0.62
  • Transcript

    • 1. IMPACTS OF LANDUSE CHANGE ON SEDIMENT TRANSPORT IN THE YALI RESERVOIR CATCHMENT Tarek Ketelsen, Luke Taylor, Mai Ky Vinh, Truong Hong CHALLENGE PROGRAM ON WATER & FOOD IN THE MEKONG: Optimizing the management of hydropower cascades at the catchment level (MK3)
    • 2. Land management options for reservoir benefits 1. Soil conservation 2. Enhancing reservoir life UPSTREAM RESERVOIR Watershed communities/ water user sectors DOWNSTREAM Water use options of reservoir for catchment benefits 1. Irrigation potential 2. Flood control 3. Fish passage requirements 4. E-flow 2
    • 3. Yali Reservoir, Viet nam Trung Nghia (TN) sub -catchment Kon Tum (KT) sub -catchment • What is the sediment inflow to Yali? • How do historic sediment loads vary with changes in flow/rainfall and land use? • What are the implications for reservoir life? 3
    • 4. Catchment suspended sediment yield (SSY) Proportion of catchment erosion which ends up in the waterways Global: (Vanoni, 1975) 10 – 20,000 t/km²/yr Mekong: (Kummu, 2010) 18 – 489 t/km²/yr 3S Basin (Kummu, 2010) 220 – 240 t/km²/yr Yali (KT & TN observation data 1990 – 2009) 79 – 1,051 t/km²/yr 4
    • 5. Large variability in Yali catchment SSY 2009: Ketsana 1996: Wukong 5
    • 6. Long term trends in SSY Annual increment in SSY in 2005-09 is ~ double the 90-97 rate 6
    • 7. Drivers of trends in SSY A. Changes in rainfall/flow regime B. Changes in land use Source: IWMI, 2002 7
    • 8. A. Long term trends in Hydrology High variability but no clear increasing trend 8
    • 9. B. Trends in land use 9
    • 10. Estimating Yali sediment inflow Trung Nghia (TN) sub -catchment 1. PECC1 official design eqn. – Kon Tum (KT) sub -catchment Based on long time series of discharge at KT 2. PECC1 empirical catchment SSY relationships – – based on long time series discharge data (1960s-1990s) at KT and TN Scaled based on ungauged area 3. Observed sediment loads KT, TN (1990-2009) – Scaled based on ungauged area 10
    • 11. Estimated Yali sediment inflow Suspended sediment yield (Mt/yr) SL Yali (Catchmnent ) Ave coarse sediment yield (Mt/yr) Suspend SL (tot) ed Load Bed load Yali (MCM) (MCM) (MCM) 2.258 0.452 1.829 0.29 2.12 6.695 1.339 5.426 0.86 6.29 0.712 0.142 0.577 0.09 0.67 SL Yali (Empirical) SL Yali (Design Calc.) 2.030 0.406 1.645 0.26 1.91 2.139 0.428 1.733 0.27 2.01 SL Yali (basin SSY) 2.423 0.485 1.964 0.31 2.28 SL Yali (Catchmnent ) Max SL Yali (Catchmnent ) Min Note: (1) Bed load was estimated based on PECC1 estimate: Bed load = 0.2* suspended load 11
    • 12. Yali Reservoir trapping efficiency • Brune’s method (1953) based on residence time of reservoir • Applied previously in the Mekong • Sesan TE: 0.851 – 0.95 (Kummu, 2010) • Yali: 0.83 12
    • 13. Yali annual sediment deposition dynamics SL(res)90-97 = 1.38 mcm SL(res) = 1.67 mcm SL(in) = 2 mcm SL(res)05-09 = 3.13 mcm SL(out) = 0.33 mcm 13
    • 14. Next (final!) steps 1. Explore sensitivity of Yali sediment inflow to land use change using the Revised Universal Soil Loss Equation – – Maximum catchment erosion (aggressive deforestation scenario) Minimised catchment erosion (aggressive afforestation scenario) 2. Estimate changes in reservoir half life based on change upland management 14
    • 15. Thank you for your attention
    • 16. Sediment delivery ratio • • Sediment transport cycle more complex and slower than water cycle Signification proportion stored in catchment: – – – – • Hillslopes Gullies Microtopographic features Human structures (check dams, reservoirs) SSY = <10% of sediment production in large catchments (>100km²) (Annandale, 2003) No. I. Kon Tum city II. Dak Gley district III. Tu Mo Rong district IV. Sa Thay district V. Ngoc Hoi district VI. Kon Plong district VII. Kon Ray VIII. Dak Ha district VIII. Dak To district TOTAL Reservoir name Total Total Main crop under irrigation Rice Rice Total Number of Reservoirs Reservoir 3 volume (m ) Total Irrigated area (ha) 10 5 10,554,000 1,188,000 1759 198 Rice 1 750,000 125 Total Rice 8 2,496,000 416 Total Rice 6 3,138,000 523 Total Rice 1 90,000 15 Total Total Rice Rice & Coffee 4 19 648,000 19,875,000 108 7236 Total Rice 15 3,048,000 508 69 % of long term mean annual inflow to Yali 41,787,000 ~0.5% 16