Soil erosion by water
EROSION
Detachment – particle/aggregate
loosened from surface
Entrainment – initiation of motion by
flow
TRANSPORT
Rill – concentrated overland flow
Inter-rill (sheetwash) – diffuse
overland flow
Detachment
Raindrop impact
Bioturbation
Frost action
Drying
Soil Conservation Service
“Curve Number” method
Empirical relationship between rainfall
and runoff 𝑄, dependent upon Curve
Number 𝐶𝑁 through the parameter 𝑆
(potential soil retention).
𝑃 − 0.2𝑆 2
𝑄=
𝑃 + 0.8𝑆
𝑆=
𝐶𝑁
− 10
1000
𝑆 may be characteristic of a plot, field,
watershed, or region according to
terrain, soil type, and land use.
Runoff generation
Runoff generation depends on
antecedent soil moisture conditions,
soil infiltration capacity, rainfall
intensity.
Runoff may be generated either when
rainfall intensity exceeds infiltration
capacity or when soil is saturated.
Green-Ampt Infiltration
Approximate physically-based
transient infiltration model.
𝑓 𝑡 =𝐾 1+
𝜓Δ𝜃
𝐹 𝑡
𝐹 𝑡 = 𝐾𝑡 + 𝜓Δ𝜃 ln 1 +
𝐹 𝑡
𝜓Δ𝜃
Where 𝑓(𝑡) and 𝐹(𝑡) are the
infiltration rate and net infiltration,
respectively.
Green-Ampt cont’d
Infiltration capacity parameters are
strongly sensitive to soil type.
Q: How does runoff flux vary with position on a
hillslope with uniform soil properties?