Soil Erosion by Water

AGSM 335 Water and Soil Management

AGSM 335 Water and Soil Management

SOIL EROSION BY WATER

READING MATERIAL CHAPTER 6 OF TEXT

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dot = 5,000 acres

red = HEL yellow = non- HEL

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Sediment Sources and Sinks
• Sources: natural erosion, ag lands, construction sites, roadway embankments, lumbered areas, surface mines • Sinks: pools and reservoirs, concave slopes, vegetation, flood plains

Principal Processes
• Detachment - dislodging of soil particles from the soil mass by erosive forces (raindrop impact, water flow, wind) • Transport - entrainment and movement of sediment from its original location • Sedimentation - deposition of transported sediment- permanent or temporary

rills => see small channels interrill area => area between rills

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Detachment
Interrill areas  raindrop impact and overland sheet flow  independent of slope length  linear function of slope steepness

soil detachment -- rainfall impact or the shearing force of water flow

Soil Erosion and Control Practices
Erosion => sediment yield => deposition  soil detachment rainfall impact / shearing force of water flow  sediment transport => flowing water  sediment yield => surface runoff velocity Decreases sediment deposited => large particles first

Sediment Transport
Transport Capacity - amount of sediment moving water is able to carry (depends on energy available-- velocity) Sediment Load - amount of sediment actually carried

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Upland SOIL Erosion
Factors • Hydrology (rainfall and runoff) •Topography • Soil type (composition, organic matter) • Soil Particle size •Land cover (interception, roughness, subsurface structure) • Land management (organic matter content, subsurface structure) • Surface roughness (depressions, tillage)

Dominant Types of Erosion

Terminology
Upland areas near watershed divide
 rills => small channels in soil

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Interrill (Sheet) - removal of a thin layer of soil particles (overland flow) Rill -