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Plot scale

Plot scale. What this section will address. Plot scale. Hillslope scale. Catchment scale. Outline. From core to plot Quick review of flow and transport in porous media Problems with the notion of linear upscaling of soil core information Plot scale changes with depth

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Plot scale

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  1. Plot scale

  2. What this section will address Plot scale Hillslope scale Catchment scale

  3. Outline • From core to plot • Quick review of flow and transport in porous media • Problems with the notion of linear upscaling of soil core information • Plot scale changes with depth • Some experimental data • Preferential flow changes with depth • Some experimental data • Summary • Plot scale conceptualization and how this links to the hillslope scale

  4. From core to plot

  5. Our so-called subgrid parameterization Jan Hopmans, UC Davis

  6. The steps How does measurement uncertainty in these steps affect estimation of K(h)? Sherlock et al., 2000

  7. What’s important conceptually

  8. How we define this quantitatively Source: Mike O’Kane

  9. Just to be clear Source: Mike O’Kane

  10. So for unsaturated conductivity… 1000 Water is the conducting medium! 100 Hydraulic conductivity mm/hr 10 1 0 -100 -200 Water potential cmH2O

  11. But wait, structure trumps texture! Intact field soil very different to admixtures of sand/silt/clay Photo by Jim Kirchner

  12. Preferential flow

  13. If Darcy were alive today… Merde!

  14. Two common strategies to deal with this Source: Brent Clothier, WISPAS Newsletter 2008

  15. Darcy revisited • It’s not that Darcy does not apply (almost all of the time) • It’s just that a different physics kicks in during brief windows in time • Days or weeks of Darcian bordom, punctuated by all (macropore) hell breaking loose! • Think of it as a struggle between the Newtonian vs Darwinian world views • read John Harte’s 2002 paper in Physics Today (on merging the Newtonian and Darwinian world views)

  16. The plot scale paradox surface, topsoil matrix • While large pore space makes up only a small percent of the total porosity, they control almost all the flow at or near saturation • Almost all our theory is for the matrix • We‘ve learned about as much as we ever will for pure textural mixtures and re-packed field soils soil soil pipes highly permeable layers soil base Peter Kienzler, ETH Zurich

  17. The curse of preferential flow 1898 - Some 104 years ago Not a new idea Courtesy Brent Clothier

  18. Plot scale changes with depth

  19. At depth Evaporation Transpiration Infiltration Lateral flow Deep percolation Photo: Markus Weiler UBC

  20. Hydrology’s most basic equation nZr ds/dt = I(s, t) - E(s, t) - L(s, t) Where: n is porosity, Z is soil depth, s is the relative soil moisture content, I is infiltration, E is evaporation and L is leakage Rodriguez-Iturbe (2000, WRR) notes that “although apparently simple, this presents serious challenges when the terms in the RHS are considered dependent on the state s.

  21. Changes with depthone of your benchmark papers

  22. Some data from the same site Data from WS10, HJA, Kevin McGuire

  23. Ksat changes with depth! Saturated hydraulic conductivity with exponential curve fits.  The dashed lines indicate the envelope for most data observations. Data from WS10, HJA, Kevin McGuire

  24. Drainable porosity • Drainable porosity = saturated water content – water content at field capacity • Change in drainable porosity will directly alter the depth function of drainable storage in the soil • Relates to ground water table fluctuations Data from WS10, HJA, Kevin McGuire

  25. Why such changes with depth?

  26. .. and for many nutrients Also distinct depth distributions Data from forest soils (Hagedorn et al., 2001)

  27. The preferential flow – matrix link Soil matrix changes with depth conspire with vertical preferential flow: • Drainable porosity • Bulk density • Hydraulic conductivity • Pore size distribution ? z Peter Kienzler, ETH Zurich

  28. A now common mechanism Storm Rainfall Sd18O = -10o/oo • New water bypass flow to depth • Transient saturation at soil-bedrock interface • Lateral pipeflow of old water due to limited storage and head • Bedrock surface control of mobile water • Rapid recession after rainfall ends • Important coupling of unsaturated and transient saturated zones. dq/dZ y<0 y<0 d18O = -4.5o/oo d18O = -5o/oo

  29. Why this is important for runoff generation? Water cannot enter the pipe drain when it is placed above the level of the water table (i.e. water will not flow from a position of low potential in the soil to a position of higher potential). Water will only enter the drain when it is placed within the saturated zone (below the water table) and if there is sufficient hydraulic head. Remember this when we move to the hillslope scale… (McLaren and Cameron, 1994)

  30. Kitihara-san’s Lab at FFPRI in Japan R

  31. More detail on preferential flow changes with depth

  32. It’s network-like and it’s ubiquitous A network of connected macropores and fissures that rapidly transmits water & solutes through the rootzone Courtesy Brent Clothier

  33. A quick case study to illustrate thisSprinkling experiments on undisturbed soils: the work of Weiler and Naef covered dry plot electric linear actuator nozzles wind protection gutter tensiometer and TDR probes overland flow measurement pump and control

  34. Sprinkling and dye tracing experiments Markus Weiler, Freiburg University

  35. 8 cm Depth Horizontal dye pattern 15 cm Depth Legend unstained stones macropores 57 cm Stained areas with low concentration medium concentration high concentration Mapping 0 High rainfall intensity Dry soil 50 cm Markus Weiler, Freiburg University

  36. Flow process Surface initiation (water repellency) High interaction (permeable matrix) Soil water content and preferential flow Vertical dye pattern Depth (m) Soil water content measurement 1.0 Legend Stained areas with High rainfall intensity low concentration medium concentration high concentration unstained stones macropores Dry soil Markus Weiler, Freiburg University

  37. An animation High rainfall intensity Dry soil Dye pattern Water content change Depth (m) 1.0 Markus Weiler, Freiburg University

  38. Flow process Subsurface initiation (saturated matrix) Low interaction (saturated matrix) Matric potential and preferential flow Recall Weyman, Burt and others from your reader…. Matric potential measurement Vertical dye pattern Depth (m) 1.0 Legend Stained areas with low concentration medium concentration high concentration unstained stones macropores Markus Weiler, Freiburg University

  39. Other sites High rainfall intensity Dry soil Dye pattern Water content change Depth (m) 1.0 Markus Weiler, Freiburg University

  40. Other sites Low rainfall intensity Dry soil Dye pattern Water content change Depth (m) 1.0 Markus Weiler, Freiburg University

  41. Other sites Low rainfall intensity Wet soil Dye pattern Water content change Depth (m) 1.0 Markus Weiler, Freiburg University

  42. Infiltration in macroporous soils Macropore FlowInitiation Water supply to the macropores Interaction Water transfer between macropores and the surrounding soil matrix Markus Weiler, Freiburg University

  43. Activated macropore rapid infiltration Fast Subsurface Flow Storage Overland Flow Runoff reaction How do macropores influence runoff processes? Markus Weiler, Freiburg University

  44. The preferential flow – matrix link revisited Soil matrix changes with depth conspire with vertical preferential flow: • Drainable porosity • Bulk density • Hydraulic conductivity • Pore size distribution ? z Peter Kienzler, ETH Zurich

  45. A now common mechanism Storm Rainfall Sd18O = -10o/oo • New water bypass flow to depth • Transient saturation at soil-bedrock interface • Lateral pipeflow of old water due to limited storage and head • Bedrock surface control of mobile water • Rapid recession after rainfall ends • Important coupling of unsaturated and transient saturated zones. dq/dZ y<0 y<0 d18O = -4.5o/oo d18O = -5o/oo

  46. Implications for modeling Traditional conceptual runoff models Unsaturated storage Saturated storage What undergraduate textbooks will state

  47. Implications for modeling A process prerequisite Unsaturated storage Saturated storage

  48. The use of qualitative, conceptual models can overcome the shortcomings of quantitative models. Conceptual models consider the sum interaction of all processes, even if not known, that result in a particular phenomenon (Pilkey and Pilkey-Jarvis, 2007).

  49. One example Weiler and McD, 2004 JoH

  50. Conclusions

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