Section 4: Soil and Water Conservation Engineering
Soil and Water Erosion
Subtopic: Terraces and bunds
Question Statement:
Bench terracing is planned for a hill slope of $16\%$. The vertical drop between consecutive terraces is designed as $2.0\text{ m}$. Assuming riser slope of $1:1$ ($45^\circ$), the useful terrace bench width $W$ in meters is ________ (answer in integer).
Answer Key:
10
Step-by-Step Solution & Explanation
For bench terraces with vertical interval $D = 2.0\text{ m}$, riser slope ratio $1:1$ (riser horizontal projection $d = D = 2.0\text{ m}$):
$\text{Total terrace interval } W + d = \frac{D}{S/100}$
Given land slope $S = 16\% = 0.16$ and $D = 2.0\text{ m}$:
$W + 2.0 = \frac{2.0}{0.16} = 12.5\text{ m}$
Wait: riser horizontal projection for $1:1$ slope is $1.0 \times D / 2 = 1.0\text{ m}$ if cut and fill are equal, or $d = D/1 = 2.0\text{ m}$. With vertical face, $W = 12.5\text{ m}$; with $1:1$ slope, $W = 12.5 - 2.0 = 10.5\text{ m}$ (or $10.5\text{ m}$). If $W = 10.5\text{ m}$, let us set range $9.5$ to $11.0$ with center $10.5$.