報告者：林雅詩 指導教授：蔡龍珆 老師 2010/12/23

1. Impact of rainstorm-triggered landslides on high turbidity in a mountain reservoirLin, G. W., Chen, H., Petley, D. N., Horng, M. J., Wu, S. J., Chuang, B., 2010. Impact of rainstorm-triggered landslides on high turbidity in a mountain reservoir. Engineering Geology. 報告者：林雅詩 指導教授：蔡龍珆 老師 2010/12/23

2. Outline • Introduction • Objectives • Study method • Results • Discussion • Conclusions

3. Introduction • Landslide is the key influence on sediment delivery in upland river catchments, which controls both amount and characteristics of sediment released. (Al-Sheriadehet al., 2000; Korup et al., 2004; Johnson et al., 2008) • Landslide is also increasingly considered as a primary factor dominating the turbidity of rivers and reservoirs. (Jordan, 2006; Sobieszczyk et al., 2007)

4. Introduction • Several studies indicate that much of the sediment produced in upper basins often does not immediately migrate downstream but is instead deposited in the riverbed, resulting in channel aggradation. (Kasai et al., 2004; Koi et al., 2008)

5. Study area – Geographical Shihmen Reservoir ------------------------------------------------------------------------------------------------------------------------------------------------------- Finishes the month July 1964 Position 24.81°N, 121.24°E effective storage capacity 309×106 m3 average annual precipitation 2556 mm slope gradient 83% 30° to 50° Flow direction southeast to northwest Fig 1. Geographical. http://www.wranb.gov.tw/ct.asp?xItem=2605&ctNode=815&mp=5

6. Study area - Geological Table 1.Formation Fig 2. Distribution of the rock formations in the Shihmen Reservoir catchment.

7. Typhoon Track Fig 3. The location of Shihmen Reservoir catchment within Taiwan and the tracks of typhoons.

8. Typhoon events

9. Typhoon events 1990 1994 1987 1992 1996 Fig 4. Sediment deposition (tonne), Annual precipitation (mm) and accumulated rainfall during typhoon (mm) during 1963~2005.

10. Typhoon events Sediment deposition (tonne) Fig 4. Sediment deposition (tonne), Annual precipitation (mm) and accumulated rainfall during typhoon (mm) during 1963~2005.

11. Objectives • To study the relationship between water turbidity and the landslide debris of the Shihmen Reservoir. • To reconstruct the process and impact of forming high turbidity water in the reservoir area.

12. Study method Statistics of Typhoon Suspended Sediment Discharge Turbidity The relationship between turbidity and landslides.

13. Term descriptions

15. Suspended sediment discharge DH-48 depth integrating suspended sediment sampler Turbidity Nephelometer 400NTU Sample ? NTU 15

16. Results analysis

17. Results analysis Fig 5. Higher water discharge could drive more landslide debris. Vertical bars indicate the standard error.

18. Results analysis Fig 6. Sediment concentration had a positive relation with the water turbidity. Dashed lines indicate the 95% confidence limits.

19. Discussion Fig 7. The diagram displays the hyperpycnal flow in the Shihmen Reservoir.

20. Conclusion • High landslide ratios do not correspond to high sediment discharge because sediment discharge is still dominated by water dischargeand landslide debris possibly still stay on slopes. • Factors causing high turbidity in the reservoir water were (1) landslides and surface weathering in the upstream catchment; (2) the high density hyperpycnal flow between upstream channel and the reservoir bottom.

21. Thanks for your attention.

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