movement of slopes due to water erosion

• what are the 3 types of water erosion processes that can move materials on slopes

  • rain splash
  • rainwash
  • rillwash
• what is rainsplash?

  • intense rain-> large raindrops splashing on bare or near bare ground
  • soil particles directly ejected or entrained in droplets that rebound from the surface
  • splashed sediments move in all directions and travel distances of a few to tens of centimeters
  • movement can occur in both upslope and downslope directions, with a progressively smaller proportion of upslope movement as slope angle increases
• what is rainwash/ sheetwash

  • refers to the washing action of rain on slopes leading to soil erosion (esp surface materials loosened up by splash erosion) by overland flow
  • about a cm in depth and does not occur as a uniform speed
  • if sheet of water is deeper (up to 1m) and faster because of intensive rainfall -> sheetflood
• what is rillwash?

  • occurs when runoff water forms tiny channels known as rills as it flows down a slope
  • rills are usually a few cm wide and deep and tend to enlarge into gullies (>0.3m)
  • materials that are eroded and transported downslope end up at the base where the gradient lessens, and velocity of the running water drops
• Formation of rills and gullies


  • Common feature of hill slopes in arid regions
• Rain in arid areas (formation of rills and gullies

  1. High runoff as it runs over hillslopes as HOF

  2. More common in deserts with thin soils, sparse vegetation cover and high rainfall intensities during rare ppt events
• Slight variations in surface topography

  • Greater depth of flow in low spots
  • Increased erosive forces over those points
• Erosion starts


  When erosive force of overland flow > resistance of surface being eroded
• Erosion


  1. Dislodges particles creating small rilles on slope surface

  2. Once water focused into ephemeral channels, positive feedback process starts

  3. Further incision creates steeper slopes drawing adjacent flow into rill
• Rill flow is deeper and faster than unconcentrated surface flow


  • Greater erosional ability
  • Develop into more enduring gullies
• Gullies


  • Tend to be deep, long, narrow and continuous or discontinuous
• Rill


  Arbitrary upper limit is less than a third of a meter wide, 2 thirds of a meter deep
• Gully


  Larger fluvial hillside channel