Page 131 - Biosystems Engineering

112 Cha pte r T h ree

Rainsplash Hydraulic
erosion erosion

Sediment Total Transport
from upland erosion, E t capacity, T c

E t < T c E t > T c

Sediment
yield
FIGURE 3.7 Conceptual framework for computing soil erosion and sediment
yield in a watershed.

3.6.2 Factors Affecting Soil Erosion and Sediment Yield
Many factors affect the rate of erosion and the sediment yield observed
at the watershed outlet. Climatic factors, soil texture and features,
land use and land cover, topography, hydrology, and geology all
affect erosion and sediment transport processes to some extent.
The effect of climate on soil erosion has been partially discussed;
rainfall is the main driving force for soil erosion. Raindrop diameter,
rainfall intensity, and duration of rainfall event are positively corre-
lated to soil erosion as discussed earlier. Longer rain events increase
soil moisture and make the soil more prone to erosion due to buoy-
ancy forces. In addition to the wind itself being a factor for soil ero-
sion, wind direction during rainfall also has a positive or negative
impact on soil erosion. Rainfall hitting the soil surface with an oblique
angle is known to detach soil particles more easily. Temperature
effects erosion through weathering of rocks.
The physical properties of soil, soil composition, and its texture
affects soil erosion in various ways. Soils rich in organic matter are
known to show high resistance to erosion. Therefore, soils rich in
humus have lower erodibility. Compacted and aggregated soils are
less susceptible to soil erosion. It is more difficult to detach particles in
smaller sizes than larger particles. Yet smaller particles are more easily
transported than larger particles. That is, clay particles are more diffi-
cult to detach than sand, but clay is more easily transported.
Land use and cover are important factors affecting soil erosion
and transport. Vegetation and plant cover reduces soil erosion by