Soil Erosion and conservation
1.Soil erosion is the removal of part of the soil by action of wind or water
2. Accelerated erosion is the most serious form of soil degradation.
3. erosion cause loss of soil to support growth of crop, silting of dams, deposition of sediment loads, causing rivers to change course, variable seasonal flow of rivers and flooding , water pollution, chemical enter water system from erosion, air pollution ,fine soil particle sin the air reduce solar radiation at the surface of the earth.
4. Loss of soil from hill slopes increases the surface runoff of water which lead to flooding in the lower parts of the watershed.
5. wind=blown sand damages crops, buildings
6. Erosion by water.
a. impact of raindrops on the soil surface
b. flow between rills and in channels down slope.
7. Loss of nutrient caused by erosion can cause a loss of yield .
8. Universal soil loss equation.
where A= annual soil loss
R= erosivity of rain
K= soil erodibility factor
L and S are length and angle of slope factors
C= crop management factor
P= soil conservation factor.
9. Acceptable limits for soil erosion
temperate climate 1 t/ ha= 900 lb/ac
R= the kinetic energy of the storm times the maximum 30 min intensity and has
values ranging form 10 to 400 Value for El Paso is 10 and for Albuquerque is 26.
the units are ft tons acre/ inch hr yr = average annual rainfall erosivity .
K is the soil erodibity factor representing the susceptibility of soil or surface material to erode, transport sediment at a given rate of runoff given a particular rainfall input as measured under a standard conditions. The standard condition is the unit plot 72.6 ft long with a 9 percent gradient , maintain in continuous fallow, tilled up and down the hill slope. The k value reflects the rat of soil loss per rainfall-runoff R erosion index. and has units of ton/ac . The values come from the soil survey table 14 and for a harkley clay loam are 0.32 ton/ac. Values are corrected for rock factors for certain part of the United States.
LS is corrected using a graph. For a field with a 0% slope and 400 ft of length , the correction factor is 0.03. For a 2 % slope the value is 0.4. For a 9 % slope the value is 1.0
The slope length is measured from the point where surface flow originates usually the top of the ridge to the outlet channel or point down slope where deposition begins.
The cropping-management fact C includes the effects of cover, crop sequence, productivity level, length of growing season, tillage practices, residue management and the expected time distribution of erosive rainstorms. The value for established grass and legume meadows is 0.4 . The values for mulch under disturbed-land conditions for straw at 2 ton /ac with 91 % cover and 84 % cover at 3 months on a 9 percent slope is 0.06 . For 1/2 ton /ac of straw with 36 percent cover the value is 0.28.
P factor is conservation factor for terracing and contouring on 9 percent slope is 0.1 and on 1-2 percent slope is not done because not terracing. For just contouring the value is 0.6 on a 1- 2 percent slope. This applied for agricultural land for disturbed range land or construction sites the values are 1.0
Calculate for following condition
El Paso R=10
Soil type harkely clay loam k = 0.32
Length 400 ft 2% slope slope LS= 0.4
Crop history is pasture = 0.40
Conservation factor countering 0.6
A= 10 *.32*.4*.4*.6= 0.3 ton/ac
Calculate the condition for the sewage desposal site
Soil type Bluepoint K= 0.15
S= 5 %
A=10*.15 *1*1*1=1.5 ton/ac
Weight of 12 inches of soil which has a density of 93.6 lb/ft^3 = 43560 ft^3/ac*96.3 lb/^3= 4194828 lb/ac =2097 ton/ac
1.5 tons = 1.5/2097 *12=0.008 inches of soil loss/ year