Using complex models and conceptualizations                     for modeling shallow landslides hydrology                 ...
“Tutto precipita”                                            Gianni Letta                         “Everything falls apart”...
IWL 2 Napoli, 28-30 Settembre 2011                                         Outline     •Hillslope Hydrology is tricky     ...
IWL 2 Napoli, 28-30 Settembre 2011                                                  Richards        First, I would say, it...
IWL 2 Napoli, 28-30 Settembre 2011                                                  Richards        First, I would say, it...
IWL 2 Napoli, 28-30 Settembre 2011                                                  Richards        First, I would say, it...
IWL 2 Napoli, 28-30 Settembre 2011                                                  Richards        First, I would say, it...
Table 12.9: Example of roughness parameters for various surfaces (Evaporation into the Atmosphere, Wilfried Brutsaert, 198...
IWL 2 Napoli, 28-30 Settembre 2011                                      6  Rigon & LanniMonday, October 10, 11
IWL 2 Napoli, 28-30 Settembre 2011                                      6  Rigon & LanniMonday, October 10, 11
IWL 2 Napoli, 28-30 Settembre 2011                                      6  Rigon & LanniMonday, October 10, 11
IWL 2 Napoli, 28-30 Settembre 2011                                      6  Rigon & LanniMonday, October 10, 11
IWL 2 Napoli, 28-30 Settembre 2011igure 2: Experimental set-up.The OpenBook schematization. (b) The initial suction head p...
IWL 2 Napoli, 28-30 Settembre 2011                               Conditions of simulation                                 ...
IWL 2 Napoli, 28-30 Settembre 2011                                      Initial Conditions                                ...
IWL 2 Napoli, 28-30 Settembre 2011- 54                                          Simulations result                LANNI ET...
IWL 2 Napoli, 28-30 Settembre 2011  Richards 3D for a hillslope- 54                        Is the flow ever steady state ?...
IWL 2 Napoli, 28-30 Settembre 2011  Richards 3D for a hillslope                         (a) DRY-Low                       ...
IWL 2 Napoli, 28-30 Settembre 2011   Richards 3D for a hillslope                        (c) DRY-High                      ...
IWL 2 Napoli, 28-30 Settembre 2011  Richards 3D for a hillslope                                 The key for understanding ...
IWL 2 Napoli, 28-30 Settembre 2011                         When simulating is understanding              •Flow is never st...
IWL 2 Napoli, 28-30 Settembre 2011                                                 The Richards equation on a plane hillsl...
IWL 2 Napoli, 28-30 Settembre 2011                                                 The Richards equation on a plane hillsl...
IWL 2 Napoli, 28-30 Settembre 2011                                                 The Richards equation on a plane hillsl...
IWL 2 Napoli, 28-30 Settembre 2011                                           The Vertical Richards Equation  Iverson, 2000...
IWL 2 Napoli, 28-30 Settembre 2011                                             The Vertical Richards Equation  Iverson, 20...
IWL 2 Napoli, 28-30 Settembre 2011                           The Vertical Richards Equation                               ...
IWL 2 Napoli, 28-30 Settembre 2011                            The Lateral Richards Equation                               ...
IWL 2 Napoli, 28-30 Settembre 2011                            The Lateral Richards Equation                               ...
IWL 2 Napoli, 28-30 Settembre 2011                                             The Decomposition of the Richards equation ...
IWL 2 Napoli, 28-30 Settembre 2011                                   When simulating is understanding                     ...
IWL 2 Napoli, 28-30 Settembre 2011                                       When simulating is understanding                 ...
IWL 2 Napoli, 28-30 Settembre 2011                                      When simulating is understanding                  ...
IWL 2 Napoli, 28-30 Settembre 2011                                       When simulating is understanding                 ...
IWL 2 Napoli, 28-30 Settembre 2011                                                             So                         ...
IWL 2 Napoli, 28-30 Settembre 2011                                                               So                       ...
IWL 2 Napoli, 28-30 Settembre 2011                  Therefore when a perched water table form                             ...
IWL 2 Napoli, 28-30 Settembre 2011                                         IS THIS TRUE ?                                W...
IWL 2 Napoli, 28-30 Settembre 2011                                              IS THIS TRUE ?                            ...
IWL 2 Napoli, 28-30 Settembre 2011                                PARAMETRIC FORMS OF THE                                H...
IWL 2 Napoli, 28-30 Settembre 2011                                      THEREFORE             •The results are strictly re...
IWL 2 Napoli, 28-30 Settembre 2011                                           Another issue                Extending Richar...
IWL 2 Napoli, 28-30 Settembre 2011                                                    Another issue                       ...
IWL 2 Napoli, 28-30 Settembre 2011                                             Or          If you do not have this extensi...
IWL 2 Napoli, 28-30 Settembre 2011                                                     In any case                        ...
IWL 2 Napoli, 28-30 Settembre 2011                                      Stability onstage                                 ...
IWL 2 Napoli, 28-30 Settembre 2011                         Infinite Slope with unsaturated conditions                     ...
IWL 2 Napoli, 28-30 Settembre 2011                         It is enough to say that a point is                         uns...
IWL 2 Napoli, 28-30 Settembre 2011         Table 3: A matrix of the times needed to achieve specific percentages of destabi...
IWL 2 Napoli, 28-30 Settembre 2011                                        Total volume of water                           ...
IWL 2 Napoli, 28-30 Settembre 2011                Table 4: A matrix of the rain volumes RF i and total water volume VF i (...
IWL 2 Napoli, 28-30 Settembre 2011                                   So simple, too simple ?             • (The evident an...
IWL 2 Napoli, 28-30 Settembre 2011                         Panola and the soil depth question                             ...
IWL 2 Napoli, 28-30 Settembre 2011                                      Soil properties          Soil (sandy-silt)        ...
IWL 2 Napoli, 28-30 Settembre 2011                 Hillslope water discharge                       o 2 peaks             ...
IWL 2 Napoli, 28-30 Settembre 2011                                                               α = 13°                  ...
IWL 2 Napoli, 28-30 Settembre 2011                                     Same as in the ideal planar case                   ...
IWL 2 Napoli, 28-30 Settembre 2011                                              Pressure growing                   Lanni e...
IWL 2 Napoli, 28-30 Settembre 2011                                      Pressure growing                                  ...
IWL 2 Napoli, 28-30 Settembre 2011                          At the time of the simulations        We were not looking at t...
IWL 2 Napoli, 28-30 Settembre 2011                                      If you tilt you slide                             ...
IWL 2 Napoli, 28-30 Settembre 2011                                In complex topography                                   ...
IWL 2 Napoli, 28-30 Settembre 2011                                      Lessons Learned         • Simple stability analysi...
IWL 2 Napoli, 28-30 Settembre 2011                         Another case and its complexity: Duron                         ...
IWL 2 Napoli, 28-30 Settembre 2011             Farabegoli et al., 2011                                       Duron stratig...
IWL 2 Napoli, 28-30 Settembre 2011              Farabegoli et al., 2011   Duron soil depth                                ...
IWL 2 Napoli, 28-30 Settembre 2011             Farabegoli et al., 2011                                       Duron geomorp...
IWL 2 Napoli, 28-30 Settembre 2011             Farabegoli et al., 2011                                       Duron soil co...
IWL 2 Napoli, 28-30 Settembre 2011                                              Duron land use                    Farabego...
IWL 2 Napoli, 28-30 Settembre 2011                                                     And a tentative association of thos...
IWL 2 Napoli, 28-30 Settembre 2011                                              Forecasting of temperature                ...
IWL 2 Napoli, 28-30 Settembre 2011                                            Soil water content at different depth       ...
IWL 2 Napoli, 28-30 Settembre 2011     Probability of landsliding                              Simoni et al, 2008         ...
Duron IWL 2 Napoli, 28-30 Settembre 2011     Probability of landsliding                              Simoni et al, 2008   ...
Duron IWL 2 Napoli, 28-30 Settembre 2011     Probability of landsliding                              Simoni et al, 2008   ...
Duron IWL 2 Napoli, 28-30 Settembre 2011     Probability of landsliding                              Simoni et al, 2008   ...
Duron IWL 2 Napoli, 28-30 Settembre 2011     Probability of landsliding                              Simoni et al, 2008   ...
Duron IWL 2 Napoli, 28-30 Settembre 2011                                      And the snow again !                        ...
Duron IWL 2 Napoli, 28-30 Settembre 2011                                  Temperature of snow !                           ...
IWL 2 Napoli, 28-30 Settembre 2011                                      Lessons Learned         • Cows count ;-)         •...
IWL 2 Napoli, 28-30 Settembre 2011                                        Credits          We are indebted to Emanuele Cor...
IWL 2 Napoli, 28-30 Settembre 2011                                                  Thank you for your attention.         ...
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An improvement of my thinking about landslide triggering. If someone needs more explanations, please write to me at riccardo.rigon at unitn.it

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Presentation given at the second I

  1. 1. Using complex models and conceptualizations for modeling shallow landslides hydrology R. Magritte - La grande marea, 1951 Riccardo Rigon e Cristiano LanniMonday, October 10, 11
  2. 2. “Tutto precipita” Gianni Letta “Everything falls apart” Gianni Letta Panta rei os potamòs Tutto scorre come un fiume Everything flows as in a river Eraclito (Sulla Natura)Monday, October 10, 11
  3. 3. IWL 2 Napoli, 28-30 Settembre 2011 Outline •Hillslope Hydrology is tricky •But, as well as landslide triggering, should be simple in simple settings •About some consequences of the current parameterization of Richards equation •So, from where all the complexity of real events comes from ? 3 Rigon & LanniMonday, October 10, 11
  4. 4. IWL 2 Napoli, 28-30 Settembre 2011 Richards First, I would say, it means that it would be better to call it, for instance: Richards-Mualem-vanGenuchten equation, since it is: ⇤⇥ ⇥ C(⇥) = ⇥ · K( w ) ⇥ (z + ⇥) ⇤t n Se = [1 + ( ⇥) )] m ⇧ ⇤ ⇥ m ⌅2 w) = Ks 1 (1 Se ) 1/m K( Se ⇤ w () w r C(⇥) := Se := ⇤⇥ ⇥s r 4 Rigon & LanniMonday, October 10, 11
  5. 5. IWL 2 Napoli, 28-30 Settembre 2011 Richards First, I would say, it means that it would be better to call it, for instance: Richards-Mualem-vanGenuchten equation, since it is: ⇤⇥ ⇥ C(⇥) = ⇥ · K( w ) ⇥ (z + ⇥) Water balance ⇤t n Se = [1 + ( ⇥) )] m ⇧ ⇤ ⇥ m ⌅2 w) = Ks 1 (1 Se ) 1/m K( Se ⇤ w () w r C(⇥) := Se := ⇤⇥ ⇥s r 4 Rigon & LanniMonday, October 10, 11
  6. 6. IWL 2 Napoli, 28-30 Settembre 2011 Richards First, I would say, it means that it would be better to call it, for instance: Richards-Mualem-vanGenuchten equation, since it is: ⇤⇥ ⇥ C(⇥) = ⇥ · K( w ) ⇥ (z + ⇥) Water balance ⇤t n Se = [1 + ( ⇥) )] m ⇧ ⇤ ⇥ m ⌅2 Parametric w) = Ks 1 (1 Se ) 1/m K( Se Mualem ⇤ w () w r C(⇥) := Se := ⇤⇥ ⇥s r 4 Rigon & LanniMonday, October 10, 11
  7. 7. IWL 2 Napoli, 28-30 Settembre 2011 Richards First, I would say, it means that it would be better to call it, for instance: Richards-Mualem-vanGenuchten equation, since it is: ⇤⇥ ⇥ C(⇥) = ⇥ · K( w ) ⇥ (z + ⇥) Water balance ⇤t n Se = [1 + ( ⇥) )] m Parametric van Genuchten ⇧ ⇤ ⇥ m ⌅2 Parametric w) = Ks 1 (1 Se ) 1/m K( Se Mualem ⇤ w () w r C(⇥) := Se := ⇤⇥ ⇥s r 4 Rigon & LanniMonday, October 10, 11
  8. 8. Table 12.9: Example of roughness parameters for various surfaces (Evaporation into the Atmosphere, Wilfried Brutsaert, 1984) IWL 2 Napoli, 28-30 Settembre 2011 Does exist a free available and reliable solver of Richards equation ? 5 Rigon & Lanni Figure 12.1: Water fluxesMonday, October 10, 11
  9. 9. IWL 2 Napoli, 28-30 Settembre 2011 6 Rigon & LanniMonday, October 10, 11
  10. 10. IWL 2 Napoli, 28-30 Settembre 2011 6 Rigon & LanniMonday, October 10, 11
  11. 11. IWL 2 Napoli, 28-30 Settembre 2011 6 Rigon & LanniMonday, October 10, 11
  12. 12. IWL 2 Napoli, 28-30 Settembre 2011 6 Rigon & LanniMonday, October 10, 11
  13. 13. IWL 2 Napoli, 28-30 Settembre 2011igure 2: Experimental set-up.The OpenBook schematization. (b) The initial suction head pr (a) The infinite hillslope hillslopeil-pixel hillslope numeration system (the case of parallel shape is shown here). Moving from 0 to 900 7sponds to moving from the crest to the toe of the hillslope Rigon & Lanni Monday, October 10, 11
  14. 14. IWL 2 Napoli, 28-30 Settembre 2011 Conditions of simulation Homogeneous soil Gentle slope Steep slope Wet Initial Conditions Intense Rainfall Moderate Rainfall Dry Initial Conditions Low Rainfall 8 Rigon & LanniMonday, October 10, 11
  15. 15. IWL 2 Napoli, 28-30 Settembre 2011 Initial Conditions 9 Rigon & LanniMonday, October 10, 11
  16. 16. IWL 2 Napoli, 28-30 Settembre 2011- 54 Simulations result LANNI ET AL.: HYDROLOGICAL ASPECTS IN THE TRIGGERING OF SHALLOW LANDSLIDES (a) DRY-Low (b) DRY-Med 10 Lanni and Rigon Rigon & Lanni Monday, October 10, 11
  17. 17. IWL 2 Napoli, 28-30 Settembre 2011 Richards 3D for a hillslope- 54 Is the flow ever steady state ? LANNI ET AL.: HYDROLOGICAL ASPECTS IN THE TRIGGERING OF SHALLOW LANDSLIDES (a) DRY-Low (b) DRY-Med 11 Lanni and Rigon Rigon & LanniMonday, October 10, 11
  18. 18. IWL 2 Napoli, 28-30 Settembre 2011 Richards 3D for a hillslope (a) DRY-Low (b) DRY-Med Simulations result (c) DRY-High (d) WET-Low 12 Lanni and Rigon Rigon & LanniMonday, October 10, 11
  19. 19. IWL 2 Napoli, 28-30 Settembre 2011 Richards 3D for a hillslope (c) DRY-High (d) WET-Low Simulations result (e) WET-Med (f) WET-High F T September 24, 2010, 9:13am D 13 A RValues of pressure head developed at the soil-bedrock interface at each point of the subcritical parallel hillslope. The Lanni and Rigon Rigon & Lannie Monday, October 10, 11 head lines represents the mean lateral gradient of pressure
  20. 20. IWL 2 Napoli, 28-30 Settembre 2011 Richards 3D for a hillslope The key for understanding Three order of magnitude faster ! (a) (b) 14 Lanni andTemporal evolution of the vertical profile of hydraulic conductivity (a) and hydraulic conductivity at the soil-bedrock interface Rigon & Lanni Figure 6: RigonMonday, October 10, 11
  21. 21. IWL 2 Napoli, 28-30 Settembre 2011 When simulating is understanding •Flow is never stationary •For the first hours, the flow is purely slope normal with no lateral movements •After water gains the bedrock and a thin capillary fringe grows, lateral flow starts •This is due to the gap between the growth of suction with respect to the increase of hydraulic conductivity 15 Rigon & LanniMonday, October 10, 11
  22. 22. IWL 2 Napoli, 28-30 Settembre 2011 The Richards equation on a plane hillslope ⇤ ⇥⌅ ⇤ ⌅ ⇤ ⇥⌅ ⇥ ) ⇥ ) C(⇥) ⇥ = ⇥ Kz cos + ⇥ Ky ⇥ + ⇥ Kx sin Iverson, 2000; Cordano and Rigon, 2008 ⇥t ⇥z ⇥z ⇥y ⇥y ⇥x ⇥x ⇥ ⇥ (z d cos )(q/Kz ) + ⇥s Bearing in mind the previous positions, the Richards equation, at hillslope scale, can be separated into two components. One, boxed in red, relative to vertical infiltration. The other, boxed in green, relative to lateral flows. 16 Rigon & LanniMonday, October 10, 11
  23. 23. IWL 2 Napoli, 28-30 Settembre 2011 The Richards equation on a plane hillslope ⇤ ⇥⌅ ⇤ ⌅ ⇤ ⇥⌅ ⇥ ) ⇥ ) C(⇥) ⇥ = ⇥ Kz cos + ⇥ Ky ⇥ + ⇥ Kx sin Iverson, 2000; Cordano and Rigon, 2008 ⇥t ⇥z ⇥z ⇥y ⇥y ⇥x ⇥x ⇥ ⇥ (z d cos )(q/Kz ) + ⇥s Bearing in mind the previous positions, the Richards equation, at hillslope scale, can be separated into two components. One, boxed in red, relative to vertical infiltration. The other, boxed in green, relative to lateral flows. 16 Rigon & LanniMonday, October 10, 11
  24. 24. IWL 2 Napoli, 28-30 Settembre 2011 The Richards equation on a plane hillslope ⇤ ⇥⌅ ⇤ ⌅ ⇤ ⇥⌅ ⇥ ) ⇥ ) C(⇥) ⇥ = ⇥ Kz cos + ⇥ Ky ⇥ + ⇥ Kx sin Iverson, 2000; Cordano and Rigon, 2008 ⇥t ⇥z ⇥z ⇥y ⇥y ⇥x ⇥x ⇥ ⇥ (z d cos )(q/Kz ) + ⇥s Bearing in mind the previous positions, the Richards equation, at hillslope scale, can be separated into two components. One, boxed in red, relative to vertical infiltration. The other, boxed in green, relative to lateral flows. 16 Rigon & LanniMonday, October 10, 11
  25. 25. IWL 2 Napoli, 28-30 Settembre 2011 The Vertical Richards Equation Iverson, 2000; Cordano and Rigon, 2008 17 Rigon & LanniMonday, October 10, 11
  26. 26. IWL 2 Napoli, 28-30 Settembre 2011 The Vertical Richards Equation Iverson, 2000; Cordano and Rigon, 2008 ⇤ ⇥⌅ ⇤⇥ ⇤ ⇤⇥ C(⇥) = Kz cos + Sr ⇤t ⇤z ⇤z Vertical infiltration: acts in a relatively fast time scale because it propagates a signal over a thickness of only a few metres 17 Rigon & LanniMonday, October 10, 11
  27. 27. IWL 2 Napoli, 28-30 Settembre 2011 The Vertical Richards Equation ⇤ ⇥⌅ ⇤⇥ ⇤ ⇤⇥ C(⇥) = Kz cos + Sr ⇤t ⇤z ⇤z In literature related to the determination of slope stability this equation assumes a very important role because fieldwork, as well as theory, teaches that the most intense variations in pressure are caused by vertical infiltrations. This subject has been studied by, among others, Iverson, 2000, and D’Odorico et al., 2003, who linearised the equations. 18 Rigon & LanniMonday, October 10, 11
  28. 28. IWL 2 Napoli, 28-30 Settembre 2011 The Lateral Richards Equation ⇤ ⌅ ⇤ ⇥⌅ ⇤ ⇤⇥ ⇤ ⇤⇥ Sr = Ky + Kx sin ⇤y ⇤y ⇤x ⇤x 19 Rigon & LanniMonday, October 10, 11
  29. 29. IWL 2 Napoli, 28-30 Settembre 2011 The Lateral Richards Equation ⇤ ⌅ ⇤ ⇥⌅ ⇤ ⇤⇥ ⇤ ⇤⇥ Sr = Ky + Kx sin ⇤y ⇤y ⇤x ⇤x Properly treated, this is reduced to groundwater lateral flow, specifically to the Boussinesq equation, which, in turn, have been integrated from SHALSTAB equations 19 Rigon & LanniMonday, October 10, 11
  30. 30. IWL 2 Napoli, 28-30 Settembre 2011 The Decomposition of the Richards equation Iverson, 2000; Cordano and Rigon, 2008 In vertical infiltration plus lateral flow is possible under the assumption that: soil depth hillslope length time scale of lateral flow constant diffusivity reference conductivity Time scale of infiltration reference hydraulic capacity 20 Rigon & LanniMonday, October 10, 11
  31. 31. IWL 2 Napoli, 28-30 Settembre 2011 When simulating is understanding •But Is the condition: verified ? courtesy of E. Cordano 21 Rigon & LanniMonday, October 10, 11
  32. 32. IWL 2 Napoli, 28-30 Settembre 2011 When simulating is understanding On the basis of the only MvG scheme, it is very difficult to say at saturation. However courtesy of E. Cordano The scale factor strongly varies with time 22 Rigon & LanniMonday, October 10, 11
  33. 33. IWL 2 Napoli, 28-30 Settembre 2011 When simulating is understanding At the beginning, at the bedrock we are we are on the red line, at the surface on the blue line courtesy of E. Cordano 23 Rigon & LanniMonday, October 10, 11
  34. 34. IWL 2 Napoli, 28-30 Settembre 2011 When simulating is understanding At the end, at the bedrock we are we are on the red line, at the surface on the blue line courtesy of E. Cordano 24 Rigon & LanniMonday, October 10, 11
  35. 35. IWL 2 Napoli, 28-30 Settembre 2011 So What happens is that, at the beginning the conditions for considering just the vertical flow are satisfied courtesy of E. Cordano 25 Rigon & LanniMonday, October 10, 11
  36. 36. IWL 2 Napoli, 28-30 Settembre 2011 So What happens is that, at the end the conditions for considering just the vertical flow are NOT satisfied. Because D0b >> D0 top courtesy of E. Cordano 26 Rigon & LanniMonday, October 10, 11
  37. 37. IWL 2 Napoli, 28-30 Settembre 2011 Therefore when a perched water table form Instead And lateral flow dominates (is as fast ) than infiltration 27 Rigon & LanniMonday, October 10, 11
  38. 38. IWL 2 Napoli, 28-30 Settembre 2011 IS THIS TRUE ? We need to go back to the basics ⇥2 f (Se ) K(Se ) = v K s Se After Mualem, 1976 f (1) Where v is an exponent expressing the connectivity between pores, evaluated by Mualem for various soil types. Se 1 f (Se ) = dx 0 (x) 28 Rigon & LanniMonday, October 10, 11
  39. 39. IWL 2 Napoli, 28-30 Settembre 2011 IS THIS TRUE ? Having defined the relative hydraulic conductivity: After Mualem, 1976 K = Ks Kr And expressed the suction in terms of van Genuchten’s expression:: 1 ⇥1/n ⇥= Se 1/m 1 The integral can be calculated: 29 Rigon & LanniMonday, October 10, 11
  40. 40. IWL 2 Napoli, 28-30 Settembre 2011 PARAMETRIC FORMS OF THE HYDRAULIC CONDUCTIVITY there results: ⇤ ⇥m ⌅2 K(Se ) = v K s Se 1 1 1/m Se (m = 1 1/n) or, by expressing everything as a function of the suction potential: ⇥2 mn n m Ks 1 ( ⇥) [1 + ( ⇥) ] K(⇥) = n mv (m = 1 1/n) [1 + ( ⇥) ] 30 Rigon & LanniMonday, October 10, 11
  41. 41. IWL 2 Napoli, 28-30 Settembre 2011 THEREFORE •The results are strictly related to the validity of the MvG theory and parameterization 31 Rigon & LanniMonday, October 10, 11
  42. 42. IWL 2 Napoli, 28-30 Settembre 2011 Another issue Extending Richards to treat the transition saturated to unsaturated zone. Is it : At saturation: what does change in time ? 32 Rigon & LanniMonday, October 10, 11
  43. 43. IWL 2 Napoli, 28-30 Settembre 2011 Another issue Extending Richards to treat the transition saturated to unsaturated zone. Which means: courtesy of M. Berti 33 Rigon & LanniMonday, October 10, 11
  44. 44. IWL 2 Napoli, 28-30 Settembre 2011 Or If you do not have this extension you cannot deal properly with from unsaturated volumes to saturated ones. where we just saw most of the phenomena of interest happens Obviously it can be done much better. Only in very special cases the specific storage can be expressed in the way we showed (e.g. Green and Wang, 1990). 34 Rigon & LanniMonday, October 10, 11
  45. 45. IWL 2 Napoli, 28-30 Settembre 2011 In any case the question relies also in the reliability of the SWRC close to saturation (e.g. Vogel et al., 2000, Schaap and vanGenuchten, 2005; Romano, 2010) courtesy of M. Berti 35 Rigon & LanniMonday, October 10, 11
  46. 46. IWL 2 Napoli, 28-30 Settembre 2011 Stability onstage The good old infinite slope 36 Rigon & LanniMonday, October 10, 11
  47. 47. IWL 2 Napoli, 28-30 Settembre 2011 Infinite Slope with unsaturated conditions The equation e.g. Lu and Godt, 2008 37 Rigon & LanniMonday, October 10, 11
  48. 48. IWL 2 Napoli, 28-30 Settembre 2011 It is enough to say that a point is unstable to state that a landslide occurs ? 38 Rigon & LanniMonday, October 10, 11
  49. 49. IWL 2 Napoli, 28-30 Settembre 2011 Table 3: A matrix of the times needed to achieve specific percentages of destabilized hillslope area for a continuous rainfall simulation for a 5-day period. A.C. RAIN SHAP E TF 5% TF 10% TF 15% TF 30% TF 50% Divergent 41h Low P arallel 41h Convergent 41h 60h DRY Divergent 14-15h 15-16h 17-18h M ed P arallel 14-15h 15-16h 16-17h 18h Convergent 14-15h 14-15h 14-15h 15h High Divergent 7-8h 8-9h 9-10h 10-11h 12h P arallel 7-8h 8h 8-9h 8-9h 8-9h Convergent 7-8h 7-8h 7-8h 7-8h 8-9h Divergent 3-4h Low Lanni and Rigon, 2011 P arallel 3-4h Convergent 3-4h 4-5h Divergent 2-3h 3-4h 4-5h W ET M ed P arallel 2-3h 3h 3-4h 4-5h Convergent 2-3h 2-3h 2-3h 2-3h Divergent 1-2h 1-2h 1-2h 3h 5h High P arallel 1-2h 1-2h 1-2h 2-3h 2-3h Convergent 1-2h 1-2h 1-2h 1-2h 1-2h 60h - - 20 h - - - 10 h - - - 5h - 0h not achieved 39 Rigon & LanniMonday, October 10, 11
  50. 50. IWL 2 Napoli, 28-30 Settembre 2011 Total volume of water in hillslope before the event remained inside the hillslope Total volume of water Total volume of in hillslope rainfall water in hillslope 40 Rigon & LanniMonday, October 10, 11
  51. 51. IWL 2 Napoli, 28-30 Settembre 2011 Table 4: A matrix of the rain volumes RF i and total water volume VF i (Rain volume + Pre-rain soil-water volume) needed to achieve specific percentages of hillslope area for a continuous rainfall simulation for a 5-day period. F 5% F 10% F 15% F 30% F 50% RAIN SHAPE DRY WET DRY WET DRY WET DRY WET DRY WET Divergent Low P arallel RF i (m3 ) Convergent Divergent M ed P arallel Convergent Divergent High P arallel Convergent Lanni and Rigon, 2011 Divergent Low P arallel Convergent VF i (m3 ) Divergent M ed P arallel Convergent Divergent High P arallel Convergent 41 15m3 - - 125m3 - - 230m3 - - 350m3 - - > 520m3 not achieved Rigon & LanniMonday, October 10, 11
  52. 52. IWL 2 Napoli, 28-30 Settembre 2011 So simple, too simple ? • (The evident and little informative statement) We found that wet volumes causes faster obtaining of instability •However, the it seems that in simple settings the total volume of water required to destabilized a certain percentage of area is not very much variable (variation is included in 10%) 42 Rigon & LanniMonday, October 10, 11
  53. 53. IWL 2 Napoli, 28-30 Settembre 2011 Panola and the soil depth question Soil-depth variability Ground surface Bedrock surface Bedrock depression 43 Rigon & LanniMonday, October 10, 11
  54. 54. IWL 2 Napoli, 28-30 Settembre 2011 Soil properties Soil (sandy-silt) Ksat = 10-4 m/s Bedrock Ksat = 10-7 m/s Rain Intensity = 6.5 mm/h Duration = 9 hours Slope α = 13° α = 20° α = 30° 44 Rigon & LanniMonday, October 10, 11
  55. 55. IWL 2 Napoli, 28-30 Settembre 2011 Hillslope water discharge o 2 peaks α = 13° t=9h t=6h t=7h t=9h t=14h t=22h Q (m3/h) t=18h Lanni et al., 2011 45 Rigon & LanniMonday, October 10, 11
  56. 56. IWL 2 Napoli, 28-30 Settembre 2011 α = 13° tim e t=6h t=7h t=9h  Saturated area at the soil-bedrock interface increases very rapidly….. 46 Rigon & LanniMonday, October 10, 11
  57. 57. IWL 2 Napoli, 28-30 Settembre 2011 Same as in the ideal planar case 1° STEP: 1D Vertical rain-infiltration Infiltration-front propagation  No role played by hillslope gradient 2° STEP: 3D Lateral-flow Lanni et al., 2011 Downslope drainage limited by bedrock topography 47 Rigon & LanniMonday, October 10, 11
  58. 58. IWL 2 Napoli, 28-30 Settembre 2011 Pressure growing Lanni et al., 2011 α = 13° α = 20° α = 30° Downslope Drainage efficiency 48 Rigon & LanniMonday, October 10, 11
  59. 59. IWL 2 Napoli, 28-30 Settembre 2011 Pressure growing α = 13° tim e t=6h t=7h Lanni et al., 2011 t=9h  …..and then the average value of positive pore-water pressure continues to grow 49 Rigon & LanniMonday, October 10, 11
  60. 60. IWL 2 Napoli, 28-30 Settembre 2011 At the time of the simulations We were not looking at this but, please observe that, increasing slope decreases instability but drainage is more efficient. Therefore there should be a specific slope angle which is, given the condition of the simulation the more unstable. 50 Rigon & LanniMonday, October 10, 11
  61. 61. IWL 2 Napoli, 28-30 Settembre 2011 If you tilt you slide α = 30° (FS=1) (1<FS<1.05) c’ = 0 kPa φ’ = 30° t=10h 51 Rigon & LanniMonday, October 10, 11
  62. 62. IWL 2 Napoli, 28-30 Settembre 2011 In complex topography of the bedrock •Topography commands the patterns of instability and convergence of fluxes can increase instability (so obvious again!) •The temporal dynamics of instabilities is also affected due to the filling and spilling effect, and different parts of the hillslope can become unstable at different times •The mechanism where infiltration comes first and lateral flow later continues to be valid •However, there is an interplay between slope and bumpiness of the bedrock which is not trivial at all. 52 Rigon & LanniMonday, October 10, 11
  63. 63. IWL 2 Napoli, 28-30 Settembre 2011 Lessons Learned • Simple stability analysis can be successful. Probably not for the right reasons • Simple settings give simple results (the total weight of water commands the creation of large instabilities) •This is due in the model to the compound of the vanGenuchten and Mualem theory (which could not be real) •Soil depths counts •On small scales instabilities could be controlled by constraints of local topography •Boundary conditions matter (trivial kinematic approaches could not work) 53 Rigon & LanniMonday, October 10, 11
  64. 64. IWL 2 Napoli, 28-30 Settembre 2011 Another case and its complexity: Duron 54 Rigon & LanniMonday, October 10, 11
  65. 65. IWL 2 Napoli, 28-30 Settembre 2011 Farabegoli et al., 2011 Duron stratigraphy 55 Rigon & LanniMonday, October 10, 11
  66. 66. IWL 2 Napoli, 28-30 Settembre 2011 Farabegoli et al., 2011 Duron soil depth 56 Rigon & LanniMonday, October 10, 11
  67. 67. IWL 2 Napoli, 28-30 Settembre 2011 Farabegoli et al., 2011 Duron geomorphology 57 Rigon & LanniMonday, October 10, 11
  68. 68. IWL 2 Napoli, 28-30 Settembre 2011 Farabegoli et al., 2011 Duron soil cover 58 Rigon & LanniMonday, October 10, 11
  69. 69. IWL 2 Napoli, 28-30 Settembre 2011 Duron land use Farabegoli et al., 2011 59 Rigon & LanniMonday, October 10, 11
  70. 70. IWL 2 Napoli, 28-30 Settembre 2011 And a tentative association of those maps with hydrological characters With Dall’Amico ,Farabegoli et al., 2011 60 Rigon & LanniMonday, October 10, 11
  71. 71. IWL 2 Napoli, 28-30 Settembre 2011 Forecasting of temperature in a point With Dall’Amico ,Farabegoli et al., 2011 In time 61 Rigon & LanniMonday, October 10, 11
  72. 72. IWL 2 Napoli, 28-30 Settembre 2011 Soil water content at different depth in a point With Dall’Amico ,Farabegoli et al., 2011 62 Rigon & LanniMonday, October 10, 11
  73. 73. IWL 2 Napoli, 28-30 Settembre 2011 Probability of landsliding Simoni et al, 2008 63 Rigon & LanniMonday, October 10, 11
  74. 74. Duron IWL 2 Napoli, 28-30 Settembre 2011 Probability of landsliding Simoni et al, 2008 64 Rigon & LanniMonday, October 10, 11
  75. 75. Duron IWL 2 Napoli, 28-30 Settembre 2011 Probability of landsliding Simoni et al, 2008 65 Rigon & LanniMonday, October 10, 11
  76. 76. Duron IWL 2 Napoli, 28-30 Settembre 2011 Probability of landsliding Simoni et al, 2008 66 Rigon & LanniMonday, October 10, 11
  77. 77. Duron IWL 2 Napoli, 28-30 Settembre 2011 Probability of landsliding Simoni et al, 2008 67 Rigon & LanniMonday, October 10, 11
  78. 78. Duron IWL 2 Napoli, 28-30 Settembre 2011 And the snow again ! 68 Rigon & LanniMonday, October 10, 11
  79. 79. Duron IWL 2 Napoli, 28-30 Settembre 2011 Temperature of snow ! 69 Rigon & LanniMonday, October 10, 11
  80. 80. IWL 2 Napoli, 28-30 Settembre 2011 Lessons Learned • Cows count ;-) •Landslide forecasting is complex for dynamical reasons •But also because it is a local phenomena where a lot of “accidents” (i.e. land-use-landcover) modify the local hydrology and the “cohesion of soils” •There is a missing link between all of those characteristics and hydrological, and geotechnical parameters •Cohesion exists but its estimation is kind of elusive when we are talking about turfs and root strength 70 Rigon & LanniMonday, October 10, 11
  81. 81. IWL 2 Napoli, 28-30 Settembre 2011 Credits We are indebted to Emanuele Cordano for the participation to some early stage of this research, and providing at late request, some plots of hydraulic diffusivity. We thank Enzo Farabegoli, Giuseppe Onorevoli and Martina Morandi for allowing to use the maps of Duron catchment which resulted after three years of detailed surveys. 71 Rigon & LanniMonday, October 10, 11
  82. 82. IWL 2 Napoli, 28-30 Settembre 2011 Thank you for your attention. G.Ulrici - 2000 ? 72 Rigon & LanniMonday, October 10, 11
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