Using the USLE, estimate the annual erosion in tonnes/year from a 100 ha foreste

ID: 1712059 • Letter: U

Question

Using the USLE, estimate the annual erosion in tonnes/year from a 100 ha forested watershed in central Colorado assuming the following:

-The forest is in fair condition with 40% cover

-The slope is 3%

-The watershed consists of 25 source areas of identical characteristics--each is approximately a square 200 m by 200 m

-The soils are clay loam in hydrologic group C

-The topography of each source area has the form of Figure 4.22(a) in the text

Figure 4.22. Representation of watersheds in simple lumped parameter rainfal- runoff mod- els: (a) V-shaped watershed: (b) cascade watershed.

According to USLE

The annual erosion factor formula is

A=RKLSCP

where A is loss of soil in tones per hectare

R is rainfall and runoff erosivity factor for given location

For colorado it is 35

K is erodiabilty factor depends on soil for clay loam it is .28

LS is tropographical factor L is slope length S-steepnes

From graphs for slope length of 200m(620ft) steepnes of 3%

Is LS=.35

C is cover and management factor for a fairly 40% cover forest it is .1

P is conservation practice factor =1

Therefore anuual loss = 35*.28*.35*.1*1=.343tons/year

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