brye swc

Types of water erosion

Raindrop splash, sheet/interrill, rill, gulley, streambank, and tunnel

Raindrop splash

• Bombardment of soil surface by raindrops falling or falling droplets of irrigation water

  • Transfers kinetic energy

  • Creates micro crater

  • Dominates initial erosion process

    • Detachment can also occur by slaking

Sheet/Inter-rill

• Rills are small, narrow channels.

• Sheet/inter-rill with raindrop splash makes up 70% of total soil erosion.

• Begins to occur immediately after raindrop splash

  • Relatively slow moving water flowing over a large, diffuse area.

  • Low slope angle

  • Shallow flow

• NO DEFINED WATER-FLOW CHANNEL

Rill erosion

• Slope increases

• Water concentrated in narrow, shallow channels

  • Dendritic-like pattern

• Rill >>>> inter-rill

• Rills fixed by tillage

Gulley erosion

• Slope increases more

• Water concentrated in larger channels

  • V or U shaped

  • > 0.3 m wide by >0.3 m deep

• Ephemeral or permanent

  • Permanent ones are too large to be corrected by tillage alone

Streambank erosion

• Collapse of banks along streams, creeks, and rivers

• Surface slump

  • Combination of water + gravity

  • Similar to sinkhole formation

• Cut bank along outer bend in a channel

• Vertical cut/exposure results

• Exacerbated by certain features along the streambank

  • Intensive tillage

  • Cattle access/hoof traffic

  • Overgrazing

  • Absence of riparian buffers/grass filter strips

Tunnel erosion

• Sub-surface flow initiated in small channels, natural cracks, and/or animal burrows

• Dispersible sub-soils most prone

  • Sodic horizons

• Seeps, lateral flow, and interflow are signs tunnel erosion may be occuring

• Surface often stabilized by roots

  • Sub-soil is loose, easily erodible

• When extensive, surface collapses

• Reclamation often includes…

  • Deep tillage

  • Haul in and repack sediments

  • Revegitation

  • Diversion of concentrated runoff and/or ponding

Two runoff producing mechanisms

Infiltration excess runoff and saturation excess runoff

Infiltration excess runoff

• Initially dry soil

• Rate of water delivery to the soil surface exceeds infiltration rate

  • Water cannot infiltrate and be redistributed away from the soil surface fast enough

• Results in runoff

Saturation excess runoff

• Soil is saturated

• All pores filled with water

  • No room for redistribution or for infiltration of any more water

  • Results in runoff

Determining Runoff in small plot areas

Cornell sprinkler infiltrometer

Determining runoff in small watershed areas

H flumes collect runoff and divert it through channel for measurement

Soil properties that affect erodibility (water erosion)

Texture, structure, surface sealing/crusting, bulk density, antecedent water content, and SOM

Air erosion transport mechanisms

Suspension

Saltation

Surface Creep

Suspension

• <0.1 mm particles "float" and scatter in the air as dust/haze

• 30 to 40% of wind erosion

• Impairs visibility, health

Saltation (“bouncing”)

• 0.1 mm to 1 mm particles bounce along surface because of weight.

• Collisions from bouncing cause abrasion and potentially more detachment, then suspension

• 50 to 70% wind erosion

Surface Creep

• ~1 mm particles roll along the surface

• 5 to 25% of wind erosion

Measuring wind erosion

Wind tunnel, Point measurements, Radionuclide fallout (Cs-137), Active/passive sampler

Erosion types

Wind, water, tillage