CPESC Soil Science 5

Question 1

What is the primary difference between 'interrill erosion' and 'rill erosion' in terms of erosive agent?

Accepted Answer

Interrill erosion is caused by raindrop impact and thin sheet flow; rill erosion is caused by concentrated channelized flow

Answer

Interrill erosion is driven by raindrop splash detachment and shallow sheet flow between rills, while rill erosion results from concentrated flow with greater shear stress.

Question 2

On a construction site, the soil texture is classified as 'CH' under the Unified Soil Classification System (USCS). What does this indicate?

Accepted Answer

High-plasticity clay with significant shrink-swell potential

Answer

In USCS, 'C' denotes clay and 'H' denotes high plasticity (liquid limit ≥50%), indicating a soil with significant shrink-swell potential and erodibility when disturbed.

Question 3

The Sodium Adsorption Ratio (SAR) of a soil is used to assess:

Accepted Answer

The risk of soil structure breakdown due to excess sodium relative to calcium and magnesium

Answer

High SAR values indicate sodium dominates the cation exchange sites, causing clay dispersion, structure degradation, reduced infiltration, and increased erosion risk.

Question 4

Which physical soil property best predicts the susceptibility of a slope to shallow landslides following prolonged rainfall?

Accepted Answer

Low cohesion combined with high saturated hydraulic conductivity in the upper profile over a restrictive layer

Answer

Shallow landslides typically occur when rapid pore pressure buildup over an impermeable layer reduces effective stress to zero in low-cohesion materials, triggering failure.

Question 5

In RUSLE modeling for a construction site, what is the typical C factor value assigned to bare, freshly graded soil?

Accepted Answer

1.0

Answer

A C factor of 1.0 represents the baseline condition of bare, fallow, tilled soil against which all other cover conditions are compared in RUSLE.

(CPESC) Certified Professional in Erosion and Sediment Control Practice Test

(CPESC) Certified Professional in Erosion and Sediment Control Practice Test

CPESC Soil Science 5