Agriculture Reference
In-Depth Information
120,000 m 2
Given, A
=
12 ha
=
Runoff depth
=
46 mm
=
0.046 m
5, 250 m 3 (Ans.)
Thus V
=
120, 000
×
0.046
=
Example 6.3
A watershed of 1,000 ha area consists of clay-loam soil. The area is covered by
pasture, wheat, and corn, and the general field slope toward the drainage outlet is
about 0.5%. A 3-h storm of 25 mm/h occurs over the watershed. The anticipant
moisture in the area was near at field capacity. Compute the peak flow rate at the
outlet of the watershed.
Solution
We know, using Rational method, peak discharge,
Q = CIA /360, m 3 /s
Here,
I
=
25 mm/h
A
1,000 ha
For the prevailing field condition, assuming C
=
=
0.65
45.13 m 3 /s (Ans.)
Putting the above values, Q
=
(0.65
×
25
×
1, 000)
/
360
=
6.5.4 Factors Affecting Soil Erosion
The major factors affecting soil erosion rates are climate (mainly rainfall), soil,
topography, and land-use pattern. The mechanisms of erosion hazard of the factors
are described below:
6.5.4.1 Climate
The most important climatic variable is rainfall erosivity, which is related to rainfall
amount (how much it rains) and intensity (how hard it rains). Another impor-
tant climatic variable is temperature because temperature and precipitation together
determine the longevity of biological materials like crop residue and applied mulch
used to control erosion.
Seasonal variations in wind, temperature, humidity, and rainfall may create more
ideal conditions for erosion.
6.5.4.2 Soils
Soils vary in their inherent erodibility. Erodibility, the property to break down soil
structure, is dependent on soil composition and texture. Soils with high erodibility
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