The application of hydrological models in shallow landslides prediction

1. The application of hydrological models in shallow landslides prediction 指導老師：李錫堤　教授 報告者： 李浩瑋 報告日期：2010/11/4

2. Outline • Introduction • Review • Objective • Method • Data • Preliminary results

3. Introduction Taiwan has been vulnerable to shallow landslide disasters caused by heavy rainfalls. Mitigate landslide disasters ： Evaluate the potential of slope failure events in space and time Lee at al., 2008 Landslide susceptibility analysis in the Tachia Creek drainage basin

4. Introduction Statistical approaches： (Fuzzy Logic, Logistic Regression, and Neural Networks…) Deterministic approaches： Physically-based models • Steady state model • SHALSTAB MODEL(Montgomery et al., 1994) • SIMMAP (Pack et al., 1998) • Transient model • TRIGRS (Baum et al., 2002) • Basic： • Modelling of slope the hydrological response • Topography is considered (Iverson, 2000)

5. Objective • To establish a slope-instability analysis and a hydrological • model for landslide prediction during heavy rainstorms. θ • FS？ Soil Ground surface Water table Sliding surface

6. Application of hydrology model • SHALSTAB • (Dietrich and Montgomery, 1994) Review • - Steady- state hydrological conditions • - Fully saturated conditions • - Homogeneous soil • - Slop-parallel groundwater flow • - Impermeable basal boundary Method Data Result • Hydrological model • Infinite slope • Critical Rainfall

7. Application of hydrology model • TRIGRS • (Baum et al., 2002) Review • - Transient hydrological conditions • - Fully saturated conditions • - Homogeneous soil • - Slope-parallel watertable • - Impermeable or infinite basal boundary Method Data Result • Infiltrate model solution of Richard’s equation Infinite slope model

8. Application of hydrology model Review • (Casadei., 2003) • - Transient hydrological conditions • - Unsaturated conditions • - Slope-parallel watertable • - Homogeneous soil • - Impermeable boundary Method Data Result • Coupled hydrological–slope stability model Groundwater table above the slip surface Infinite slope model

9. Flow chart Input data Rainfall Data DEM Data Area Data Soil Parameter Groundwater level Estimation model Hydrologic Parameter Infinite Slope Stability Model Output data Groundwater Height Safety Factor Landslide susceptibility Map

10. Hydrologic Model Stream line Contour line Upslope contributing area a TOPMODEL(TOPgraphy based hydrological MODEL)(Beven. et al., 1979) Review Method Data Result

11. Topographic index Review a： Specific area tan β ：slope Method Data Result

12. TOPMODEL Structure Review Method Data Srz Result Suz Groundwater table qv Zw Srz： Root zone Suz： Unsaturated zone D：SoilDepth Zw：Water table height qv：垂直入滲率

13. TOPMODEL Assumption Saturated defict, zj This equation can be solved for z: Steady-state

14. Hydrologic Routing Review Method Data • The recharge to the groundwater table Result • The baseflow from the saturated zone

15. Hydrologic Routing Review Method Data • The recharge to the groundwater table Result • The baseflow from the saturated zone

16. Infinite Slope MODEL Review 依據有效應力概念，土體之阻滯力 τr 表示如下 Method Data 土體之駟動力τd為飽和土體沿坡面之分力 Result FS>1 Stable FS<1 Unstable

17. Infinite Slope MODEL Review Method Saturation ,W Data Result TOPMODEL calculate local storage deficit Zi Distribution of the soil saturation induced slope instability

18. Study Area Review Method Data Result

19. Study Area Review Method Data Result

20. Geological Map Review Method Data Result

21. Geo-material Parameter Review Method Data Result

22. TOPMODEL Parameter Review Method Data Result

23. Landslides induced by AERE Typhoon Review Method Data Result

24. Topographic index Review Method Data Result

25. Local saturation deficits Given • m=0.032 • . • Compute • l=5.43 Review Method T=0 Data Result

26. Soil profile saturation Review • Saturation> 1.0, Set to 1.0 • Saturation< 0 , Setto 0 Method Zi Data Result

27. Soil profile saturation Review Method Data Result

28. Rainfall Process Review T=36 Method Data Result

29. Prediction T=36 Review Method Data Result Distribution map of slope failures of actual vs predicted by model

30. Classification Error Matrix Review Method Data 非山崩網格 Result 山崩網格 預測的山崩網格，坐落 於非山崩網格中 預測的山崩網格，坐落 於山崩網格中

31. Classification Error Matrix Review The results of both are quantitatively compared by using two following evaluation indexes. AR= ( N1 ) / ( N1+ N2+ N3+ N4)(1) FAR= ( N3 ) / ( N1+ N2+ N3+ N4)(2) Here, AR is accuracy rate (%), FAR is false alarm rate (%) and N1, N2, N3 and N4 (see Table ) Method Data Result N1, N2, N3, N4 : number of cell on each category

32. Classification Error Matrix Review The results of both are quantitatively compared by using two following evaluation indexes. Method Data Result N1, N2, N3, N4 : number of cell on each category AR= 57.61%

33. 崩塌地分析成果及評估 文獻回顧 正確率的計算方式可以分類誤差矩陣表（classification error matrix）進行表示，其計算方式如下： 研究方法 Total=121809 研究資料 初步成果 未來工作 山崩正確率=57.61% 非山崩正確率=88.91% 總體正確率=88.62%

34. Future Work • Calibration parameter • Model validation • Comparing the results

35. Thank you for your attention