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RATIONALE

RATIONALE. CERTAIN TRUTHS ARE SELF-EVIDENT. EROSION IS A SOIL GEOMORPHIC PROCESS BASIC TO THE NRCS nee SCS. OBJECTIVES. The participant will: construct, label and explain a Hjulstrom’s Diagram; relate erosion to ground cover; and

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RATIONALE

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  1. RATIONALE CERTAIN TRUTHS ARE SELF-EVIDENT. EROSION IS A SOIL GEOMORPHIC PROCESS BASIC TO THE NRCS nee SCS. OBJECTIVES • The participant will: • construct, label and explain a Hjulstrom’s Diagram; • relate erosion to ground cover; and • explain slope shape, slope length, slope gradient using diagrams and in terms of slope processes. 1 5/3/2012

  2. MOUNTAIN TERRAIN IN CONTINOUS USE FOR AGRICULTURE FOR 800 + YEARS. 4 Basics of EROSION COVER THE SOIL; LENGTHEN THE FLOW; LOWERGRADIENT OF FLOW; USE THE WATER CONSUMPTIVELY. Hills above Pissac, Peru 2 JL Richardson Photo

  3. Slide 4 “Water Flow & Transport”: white lettering “1/2mile; rejuvenate;” Not clear to me what this means, or how it adds to the central point. Slide 25: “Combat landslides” probably should go w other landslide materials, so I moved it back there. Note that the slides. EROSION - Basic Concepts • EROSION is the DETACHMENT & MOVEMENT of soil or rock materials by wind, water, ice, or gravity. • DETACHMENT requires more energy but it does NOT have to be sustained. • TRANSPORTATION requires sustained fluid energy. • OBJECTIVE: EXPLAIN the above concepts by drawing, labeling Hjulstrom’s Diagram 3

  4. WATER FLOW & TRANSPORT SURFACE RUNOFF (Suspended Load) External impact Water moves rapidly Creates “youth” 1/2mile surface flow/day, which rejuvenate landscape. SUBSURFACE FLOW (Dissolved Load) Internal impact Water moves slowly; creates “age” 4

  5. EROSION - Basic Concepts pt2 • Erosivity is kinetic energy of wind & water acting on the soil-landscape. • Wind velocity, raindrop size, rainfall intensity, melting speed of snow, amount of precipitation are examples of erosive actions. • Erodibility is the ability to withstand erosive conditions by soil landscapes. 5

  6. Erosion 1000 100 10 1.0 0.1 HJULSTROM’S DIAGRAM EROSIVITY (Y-Axis) Detachment line Transport LOG AVERAGE VELOCITY (cm/sec) Deposition vfs ERODIBLITY(X-Axis) Initial deposit line .001 .01 0.1 1.0 10 100 LOG PARTICLE DIAMETER mm) Hjulstrom, F. 1939. Transportation of detritus by moving water. In Trask, P.D. Recent Marine Sediments. pp5-47. (reissued by Dover Press, NY) 6

  7. Bagnold Wishmeyer LDMeyer Hjulstrom Savant, (1982) 7

  8. EROSION - Basic Concepts pt3 • Erodibility includes soil texture, landscape factors, frozen versus unfrozen ground, vegetation or ground cover, and many other factors. • Accelerated erosion is: • erosion that is more rapid than geologic erosion, • results from the action of hominids or other animals (e.g., goats). 8

  9. Water Drop as a Direct Hit 8 9 (cover of SSSJ )

  10. RAINDROP SPLASHsize matters VELOCITY SIZE b R H a W RIM CRATER 10

  11. HORTON’S BASIC EQUATION & LANDSCAPE RAIN (P) P=Ei+I+Ho Ei (Interception) ZONE OF NO EROSION Ho= overland flow I = infiltration EROSION ZONE I ZONE OF DEPOSITION Ho Horton 1945 11

  12. ERODIBILITY (Y axis) OF NATIVE VEGETATION AS A FUNCTION OF EROSIVITY (X axis) Shrub Desert Grasslands Forest EROSION 0 10 20 30 EFFECTIVE RAINFALL (in.) Source: Langbein & Schumm1958 12

  13. UNIVERSAL SOIL LOSS EQUATION • E = RKSLPC • R = EROSIVITY; CLIMATE AND WEATHER; “THAT STORM WAS EROSIVE.” • P & C = PLANT COVER FACTORS • K = ERODIBILITY OF SOIL TEXTURE • S & L = SLOPE FACTORS Wishmeyer and Smith 1978 13

  14. SLOPE GRADIENT WATER FLOWS FASTER ON STEEP SLOPES ERODIBLE NOT ERODIBLE 14

  15. SLOPE LENGTH LONG SLOPES HAVE A LARGER VOLUME OF WATER AT THE BASE OF THE SLOPE. SLOPE WATER VOLUME EROSION IS GREATEST AT THE BASE OF A LONG SLOPE. 15

  16. SLOPE PROFILES-1Erosional Landscape RIDGE HEAD SLOPE COVE 6 4 2 NOSE VALLEY CONTOUR INTERVFAL 2 m 16

  17. SLOPE PROFILES-2 NOSE SLOPE LOW WATER VOLUME Short Length; High Gradient HEAD SLOPE HIGH WATER VOLUME Long Length; High Gradient 17

  18. SLOPE SHAPE ELEV. (ft) CONVEX UNIFORM 20 CONCAVE 10 0 200 after Meyer & Kramer 1969 SLOPE LENGTH (ft.) 18

  19. SLOPE SHAPE part II SED (T.) CONVEX 0.8 0.4 UNIFORM CONCAVE 0 200 after Meyer & Kramer 1969 SLOPE LENGTH (ft.) 19

  20. Created Slopes after MiningCHEAPEST CONVEX Max Slope Max Water Easy to Create Slope MAXIMUM WATER VOLUME MAXIMUM SLOPE • ERODIBILITY • Gradient -- Steeper more erodible • Water Volume -- More water means more erosion. 20 (Wollenhaupt, and Richardson, 1982)

  21. Created Slopes after MiningLowest Erosion MAXIMUM SLOPE Greatest natural productivity for range Largest yield for crops Recommended Slope GENTLE CONCAVE MAXIMIZES WATER INFILTRATION MAXIMUM WATER VOLUME • ERODIBILITY • Gradient -- Steeper more erodible • Water Volume -- More water means more erosion. 21 (Wollenhaupt, and Richardson, 1982) 10

  22. POP QUIZ Diagram and label Hjulstrom'sdiagram. Explain the diagram using concepts of erosivity, erodibility, detachment and transport. FROM HERE ON THE IMAGES ARE REALLY AN APPENDICE 22

  23. WAVE INFLUENCED EDGESMAP UNITS FROM KOSSUTH CO., IA WAVE-CUT ESCARPMENT WAVE-BUILT TERRACE 138B OFF-SHORE 511 62D WAVE-CUT TERRACE 73C2 • Lower gradient enhances infiltration. • Coarse textures enhance infiltration and groundwater movement. • Fine textures in the pond interior retard discharge.

  24. TILLAGE CREEP JOHN DEERE MOVEMENT Net down slope movement of soil Plow Share Tilled soil DeAlba, S., M. Lindstrom, T.E. Schumacher, D.S. Malo. 2004. Soil landscape evolution due to Soil redistribution by tillage. Catena 58:77-100.

  25. Stream Erosion ona meander Cut Bank CUTS ON THE OUTSIDE DEPOSITS ON THE INSIDE Point Bar Stream Power on Bed Weak (1) to strong (5) 5 1 Maximum Erosive Energy See Lindbo & Richardson 2001 and Allen, JRL.1970 Cutting power on the outside (CUT BANK) where maximum velocity combines with largest water volume. Erosion directly proportional to water volume and velocity. Epw = k Q s where Q is amount of water and s is flow speed; k just makes the equation balance. Epw is erosive power..

  26. What problems exist at the arrows? LIST THE MISTAKES MADE HERE. ENTRENCHED RED RIVER between MN and ND.

  27. Types of Sediment Transport • Saltation and traction are called “bed load” if associated with stream channels.

  28. Types of Sediment Transport • Suspension (suspended load) is the lofting into suspension of particles and distant transport. These deposits tend to be blanket deposits with little recognizable bedding. Loess and off-shore sediments are examples of suspended load deposits.

  29. D Flotation CURRENT MATERIAL TRANSPORT PROCESSES Suspension Solution Saltation Traction After (Selley, 1988) A suspension D flotation B saltation E solution C traction (channel bed load / traction carpet ) ( after Selley, 1978 )

  30. MATERIALS TRANSPORTquiz • The student will diagram, label and explain the 5 concepts of materials transport.

  31. TYPES OF SEDIMENT TRANSPORT • TRACTION - sliding, rolling or tumbling in channels or in a landslide or other mass wastage phenomena. • SALTATION - hopping or bouncing particle movement. Turbulent fluid movement lifts particles but cannot sustain transport. Sand dunes result from saltation.

  32. DIFFERENTIAL TRANSPORT & SORTING • CHEMICAL (dissolved load) mobility sequence or leaching sequence Na, Ca, Fe2+, Mg, K, Si, Al, Fe3+ Evaporite sequence. • PHYSICAL (see Hjulstrom’s Diagram) • Gravel, coarse sand, sand, fine sand, very fine sand and silt, silt and clay

  33. EROSION BY WIND SOIL ERODED(/ACRE) LOAM TEXTURE with CALCITE; WIDTH 1320 FT. FALL TILLAGE EAST-WEST 16t SMOOTH TILLED ROUGH TILLED 0 100 % 0 % GROUND COVERED BY RESIDUE University of Minnesota Agr. Ext. Service

  34. Questions 1.Why is the Yellow River Yellow? 2. Landslides, Creep, Detachment, Transportation, Hjulstroms Diagram, Rills, Gullies, Slump, Cut-Bank, Rain-Drop Splash, Long Slopes, Gradient, Ground Cover, and land management are concepts of ? 3. Where has all the SNIRT (snow and dirt) GONE? (Winter Aeolian erosion and deposition). Farm bill in several states has required ?___which has reduced winter erosion.

  35. QUESTIONS cont. • Why do we say: “that stream is silted in”? • For the geologists, landslides are like (normal or reverse) faults. • We combat landslides by • drainage; • removal of weight from the top; • adding weight to the bottom; • stabilizing with cements like CaO reactions to create a soil cement. • Wetland edges receive most of the _______ sediment at the edge and the_______ sediments in the center.

  36. QUIZ • According to Universal Soil Loss Equation, base of slopes erode faster that the upper areas of the same slope. Why in plowed till landscapes of western Minnesota is this NOT true? Why was it true in “restored” slopes at lignite mines in western ND. • Slope gradient, slope length and slope ____________ are the slope factors.

  37. γ = bulk density; shear stress τ = γ z cos*sin Θ; Normal stress σ = γ z cos2Θ Mohr-Coulomb Law τ = c + σ tan Θ; In thin slides in coarse materials cohesion (c ) assumed to nil. Θ W Θ Internal friction angle z t Shear stress σ Normal stress (mostly due to W or weight) SLOPE STABILITY THIS FAILURE SURFACE R. Handy personal communication

  38. Slump Block PUSHING PUSHED

  39. COMBAT LANDSLIDES:1. UNLOAD TOP of HILL; 2. LOAD BOTTOM of HILL;3. DRAIN the ENTIRE HILL; 4. see book Tension Crack Watered Lawn House τ = c + σtan f Shear stress = cohesion + normal Stress*tangent friction angle Mohr-Coulomb Law Garage Excavation Removed For Houses Viewed Failure Zone Impervious Shale Till FROM R. HANDY’S CLASS

  40. LANDSLIDES IN PIERRE SHALE ZONE 1 ZONE 2 No streams occur in the slide zones, although the slopes are often > 15%.

  41. EROSION by SLIDING • List as many factors as you can that contribute to landslides. • Why are the loess hills in western Iowa so steep? Shear stress relates to normal stress (weight), ___________, and __________. • What is plasticity, plastic failure, geostatic stress, hydrostatic stress, and lateral stress? Which of the latter three relates basement wall failure in Vertisols?

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