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 CATCHMENTTarek 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)
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UPSTREAM
RESERVOIR
DOWNSTREAMWater use options of reservoir for catchment benefits1. Irrigation potential2. Flood control3. Fish passage requirements4. E-flow
Watershed communities/
water user sectors
Land management options for reservoir benefits1. Soil conservation 2. Enhancing reservoir life
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Yali Reservoir, Vietnam• 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?
Trung Nghia (TN) sub -catchment
Kon Tum (KT) sub -catchment
Catchment suspended sediment yield (SSY)
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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
Proportion of catchment erosion which ends up in the waterways
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Large variability in Yali catchment SSY
2009: Ketsana1996: Wukong
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Long term trends in SSY
Annual increment in SSY in 2005-09 is ~ double the 90-97 rate
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Drivers of trends in SSY
Source: IWMI, 2002
A. Changes in rainfall/flow regime
B. Changes in land use
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A. Long term trends in Hydrology
High variability but no clear increasing trend
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B. Trends in land use
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Trung Nghia (TN) sub -catchment
Kon Tum (KT) sub -catchment
1. PECC1 official design eqn.– 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
Estimating Yali sediment inflow
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Estimated Yali sediment inflowSuspended sediment yield (Mt/yr)
coarse sediment yield (Mt/yr)
Suspended Load (MCM)
Bed load (MCM)
SL (tot) Yali (MCM)
SL Yali (Catchmnent ) Ave 2.258 0.452 1.829 0.29 2.12
SL Yali (Catchmnent ) Max 6.695 1.339 5.426 0.86 6.29 SL Yali (Catchmnent ) Min 0.712 0.142 0.577 0.09 0.67
SL Yali (Empirical) 2.030 0.406 1.645 0.26 1.91 SL Yali (Design Calc.) 2.139 0.428 1.733 0.27 2.01
SL Yali (basin SSY) 2.423 0.485 1.964 0.31 2.28
Note:(1) Bed load was estimated based on PECC1 estimate:
Bed load = 0.2* suspended load
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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
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Yali annual sediment deposition dynamics
SL(in) = 2 mcmSL(res) = 1.67 mcm
SL(out) = 0.33 mcm
SL(res)05-09 = 3.13 mcm
SL(res)90-97 = 1.38 mcm
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Next (final!) steps1. 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
Thank you for your attention
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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. Reservoir name
Main crop under irrigation
Number of Reservoirs
Reservoir volume (m3)
Total Irrigated area (ha)
I. Kon Tum city Total Rice 10 10,554,000 1759II. Dak Gley district
Total Rice 5 1,188,000 198
III. Tu Mo Rong district
Total Rice 1 750,000 125
IV. Sa Thay district
Total Rice 8 2,496,000 416
V. Ngoc Hoi district
Total Rice 6 3,138,000 523
VI. Kon Plong district
Total Rice 1 90,000 15
VII. Kon Ray Total Rice 4 648,000 108VIII. Dak Ha district
Total Rice & Coffee 19 19,875,000 7236
VIII. Dak To district
Total Rice 15 3,048,000 508
TOTAL 69 41,787,000 ~0.5%% of long term mean annual inflow to Yali