4. Soil Erosion by Water Flashcards by Blessed Angela Lascuña

a process by which soil is removed from the
Earth’s surface by exogenetic processes
such as wind or water flow, and then
transported and deposited in other
locations.

soil erosion

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____ hold soil solid with their roots.
Without them, erosion can lead to
landslides & floods

trees

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natural erosion (soil-forming and soil
eroding processes) which maintain the
soil in favorable balance.

geological erosion

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abnormal erosion as a result of
human activities.

accelerated erosion

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removal of surface soil takes place
at much faster rate than it can be
built up by the soil forming
processes

ACCELERATED EROSION

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forces involved in accelerated erosion

attacking forces
resisting forces

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remove and transport the soil particles

attacking forces

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retard erosion

resisting forces

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TWO INTERACTIVE PROCESSES

DETACHMENT of soil particles from the soil surface.
TRANSPORT of detached particles.

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without the _______,
erosion will not even start

detachment process

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without the ______,
erosion will be much limited

transport process

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EROSION SUB-PROCESSES

Detachment by rainfall
Transport by rainfall
Detachment (scour) by runoff (overland or channelized flow)
Transport by runoff

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rainfall amount, intensity and energy
all impact erosion rates

climate

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erosion due to raindrop splash and
shallow overland flow varies with the
_____

rainfall intensity

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____ physical properties affect
infiltration capacity

soil

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______ increases as the
size of the soil particles increases

soil detachability

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_____ increases with a
decrease in the particle or aggregate
size.

soil transportability

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interception of rainfall, reducing
surface sealing and runoff

vegetation

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retardation of erosion by resisting
erosive forces

vegetation

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decreases soil water,
increased storage capacity, less
runoff.

transpiration

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slope length and steepness, shape
and size and shape of the watershed

topography

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on _____, soil is more easily
detached and transported
downslope

steep slopes

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on _____, an increased
accumulation of overland flow tends
to increase concentrated flow
erosion

longer slopes

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_____ with flatter slopes
at the foot of the hill, deliver less
sediment than convex slopes.

concave slopes.

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- can be naturals such as prolonged periods of wet weather - human induced such as construction or tillage

disturbances

the greatest natural disturbances in the ecosystems

fire

may disturb the soil

agricultural practices

also called as splash erosion

raindrop erosion

- soil detachment and transport resulting from the action of raindrop - the first stage of soil erosion by water

raindrop erosion

raindrops increase____, providing a greater sediment-carrying capacity

turbulence

the splashed particles can rise as high as ___ above the ground and move up to ____ from the point of impact

0.60 m; 1.5 m

- the removal of soil in thin layers by raindrop impact and shallow surface flow - its soil detaching and transporting capabilities are small

sheet erosion

results in loss of the finest soil particles that contain nutrients and organic matter in the soil

skimming

are most vulnerable to sheet erosion

overgrazed and cultivated soils with less vegetation

the intermittent process of transforming to gully erosion

rill erosion

are shallow drainage lines < 30 cm deep and 50 cm wide

rill erosion

- common in bare agricultural land, overgrazed land and freshly tilled soil where soil structure has been loosened - the rills can be obliterated by tillage

rill erosion

the advanced stage of rills

gully erosion

is formed when the depth and width of the rill is > 50 cm

gully

- are deeper channels and cannot be removed by normal cultivation - flows have high erosive power - produce sediment that may clog downstream

gullies

4 classes of gullies depending upon the depth and width

G1, G2, G3 and G4

STAGES OF GULLY DEVELOPMENT

1. FORMATION STAGE 2. DEVELOPMENT STAGE 3. HEALING STAGE 4. STABILIZATION STAGE

PROCESSES OF GULLY FORMATION

1. Waterfall erosion 2. Channel erosion 3. Alternate freezing and melting of snow 4. Undercutting, landslides, mass movements of soil

most of the soil erosion equations were developed in US basically, splash and sheet erosion estimation

SOIL LOSS ESTIMATION

E = CS^m1L^M2

E = soil loss per unit area from a land slope of unit width; C = constant reflecting the combined effect of rainfall, soil cover and cover management practices. S = slope; L = horizontal length of slope, and m1 and m2 = exponents with estimated values of 1.4 and 0.6, respectively

advocated the development of erosion research on splash erosion. He suggested that splash erosion is a function of soil and rainfall properties

Ellison (1945 and 1947)

commonly known as the slope-practice equation but sometimes referred to as

Musgrave equation

developed an expression for the claypan soils of Missouri, expressed sheet erosion as

Smith and Whitt (1947 and 1948)

has gained wide acceptance in the United States and has been adapted by soil conservationists in other countries its popularity is due to its simplicity and the absence of alternative equations allowing a wider range of variations of the parameters that are contributing to soil erosion

THE UNIVERSAL SOIL LOSS ESTIMATION (USLE)

USLE

THE UNIVERSAL SOIL LOSS ESTIMATION

it estimates sheet erosion as the product of a series of terms for rainfall, soil, slope gradient, slope length, crop and cover management and conservation factors

USLE

in areas where the USLE applies, it serves as a useful tool for soil conservationists it can be used to:

a. predict soil erosion losses b. guide the selection of agricultural practices such as cropping and management systems c. guide in determining the on-site effects of land use and crop management changes d. provide baseline data for conservation planning

in the absence of any applicable method for estimating soil erosion rates in tropical Asia, _____ modified the Universal Soil Loss Equation to suit locally available information and prevailing environmental conditions

David (1986), David and Collado (1987)

- a quantitative measure of erosion potential of rain - allows for spatial estimation of basic erosion risks in different areas

RAINFALL EROSIVITY, R

is reached after 5m fall

erosive energy of raindrop

KE of falling raindrop is ____

0.5mv2

the higher the rainfall, the ____ the erosion hazard

higher

30-60 mm/hr intensities

10% of rain is erosive

>100 mm/hr

all the rain is erosive

5% is erosive in temperate

40% in tropical

is determined by computing KE for each equal intensity period of storm, multiplied by the RF amount for that period; then these are summed and multiplies by the max. 30-min intensity of the storm

erosivity factor (R)