1. Post-event reconstruction of the short- lived Siaolin landslide dam Advisor ： J.J. Dong Presenter ： Y.S. Li Date ： 2010/10/14 莫拉克颱風引致之堰塞湖地形與水文參數分析－ 以小林村堰塞湖為例

2. Outline Introduction Methods Results The characteristics and failure mechanisms of the Siaolin landslide dam Conclusions Future works

3. Introduction(1/3) Formation of landslide dams ： Longevity of landslide dams ： (Casagli and Ermini,2003) (Costa and Schuster,1986 ) Stability

4. Introduction(2/3) Stability of landslide dams : (Dong et al.,2009) DBI : ： catchment area ： dam height ： dam volume Discriminant analysis ： ： peak flow ： dam height ： dam width ( along the valley) ： dam length( across the valley) Ds ＞ 0 ： Stable Ds ＜ 0 ： Unstable (Dong et al.,2009) (Ermini and Casagli,2003 )

5. Introduction(3/3) Why ? The database of landslide dams is incompleteness. → Lacked for systematic data gathering on process, characteristics, control measures, and effects of landslide dams. (Costa and Schuster, 1986) →The forming and breaching of rainfall triggered landslide dam is beneficial to understand the impact of extreme weather on surface process relates to landslide dam. (Kroup, 2004) →Detailed documentation of processes of dam failure remained scare. (Kroup, 2002) So … Morakot event. → The Siaolin landslide dam. → Reconstruction of the shape of landslide dam.

6. ASTM→ Grain size distributions of dam materials. 2. Field investigation Methods Reconstruction of dam geometry Topography Debris budget of landslide Debris budget of landslide Inflow rate and overtopping time 1. Aerial photographs1. Laboratory works 2. Debris budget DTM. Field investigation & Laboratory works. Kriging. 2. Inflow rate is 2974cms. → overtopping time. 1. Water level. →Water volume. (based on DTM) (Hungr and Evans,2004) Volume of debris entered the channel. Initial volume of a landslide. volume expansion due to fragmention. Volume of debris deposit on the slope. Volume of the entrained materials.

7. Results(1/5) Topographic Analysis Laboratory works Fine grain particles Lower Hydraulic conductivity Overflow ● ● EL. 440 EL. 420

8. Results(2/5) Volume and debris budget of landslide 25.21 million m 3 2.23 million m 3 13.33%15.41 million m 3 15.31 million m 3 Reference value

9. Results(3/5) Dam height ● EL. 410 ● EL. 440 ● EL. 420 No.11 Bridge

10. Results(4/5) Reconstruction of the shape of landslide dam

11. Results(5/5) The total dam volume is 15.34 million m 3. 15.31 million m 3 The maximum thickness of deposition is 60 m. The breached dam volume is 7.36 million m 3. The maximum thickness of erosion is 41 m.

12. The characteristics and failure mechanisms of the Siaolin landslide dam Characteristics 欄位名稱結果 堰塞湖天然壩座標 X=120°38'52" ; Y=23°10'19" 發生年 2009/08/07-2009/08/09 名稱旗山溪堰塞湖 誘因降雨導致崩塌土石堵塞淇山溪河道 集水區面積 354067960.758m 2 水系次數 3 平均流量 30.14cms 尖峰流量 2974cms 上游坡降約 7.6% 下游坡降約 1.0% 壩體組成材料與地質 SC 、 SM 、糖恩山砂岩 ( 上新世 ) 山崩移動土塊量 25210743.35m 3 山崩發生源面積 627294m 2 山崩水平滑距 2916.69m 比高 875m 壩高 damA=27.36m ( 平均壩高 ) damA=54m ( 縱剖面最高點的壩高 ) damA=44m (Breaching point 壩高 ) damA=60 m( 最大壩高 ) 壩長 damA=1553.6m 壩寬 damA=486.68m ( 平均壩寬 ) damA=760m( 縱剖面最高點的壩寬 ) 湖水深 35m 湖面積 73350 m 2 壩體積 damA=13179396.26m 3 ; damB=2161888.972m 3 湖體積 9876559.36 m 3 壽命約 44 分鐘 Failure mechanisms DBI=3.2 ； D s = -0.37Unstable Matrix-supported. Overtopping FS=3.46 Piping FS=3.46 Slope X X

13. Conclusions The total volume of landslide dam is estimated to be 15.34 million m 3, the dam height of breaching point is 44m, the maximum dam height is 60m, the dam length(along valley) and dam width(across valley) is 1554m and 760m. According to dam materials and estimated geometry and hydrologic parameters ： → The Siaolin landslide dam is classified as unstable and failure mechanism is dominated by overtopping.

14. Future works 3D landslide dam. Collecting the data of landslide dams during Morakot typhoon.

15. Thanks for your attention ！