Question

Bench terracing is to be done on a 25% sloped land with riser slope of 1:1 and width of level terrace as 6 m. The vertical interval for terraces will be:

• A. 1 m
• B. 2 m
• C. 3.3 m
• D. 4 m

Hint:

For any terracing problem, always draw a simple cross-section diagram. The fundamental relationship is always: Original Land Slope = (Vertical Interval) / (Width of Terrace + Horizontal equivalent of Riser).

Answer 1

The Correct Option is B

Step 1: Visualize the geometry of the bench terrace.
A bench terrace replaces a steep slope with a series of flat steps (the terrace) and steep risers. The original land slope is the ratio of the total vertical drop to the total horizontal distance.
Let VI be the Vertical Interval (height of the riser) and W be the width of the flat terrace.
Step 2: Relate the components to the original land slope.
- The vertical drop for one terrace unit is VI.
- The horizontal distance for one unit consists of the terrace width (W) and the horizontal base of the riser.
- Since the riser slope is 1:1 (vertical:horizontal), its horizontal base is also equal to VI.
- Total horizontal distance per unit = W + VI.
Step 3: Set up the slope equation and solve for VI.
The original land slope is given as 25%, which means a slope of 0.25. \[ \text{Slope} = \frac{\text{Total Vertical Drop}}{\text{Total Horizontal Distance}} \] \[ 0.25 = \frac{VI}{W + VI} \] Substitute the given terrace width, \(W = 6\) m: \[ 0.25 = \frac{VI}{6 + VI} \] \[ 0.25 \times (6 + VI) = VI \] \[ 1.5 + 0.25 \cdot VI = VI \] \[ 1.5 = VI - 0.25 \cdot VI \] \[ 1.5 = 0.75 \cdot VI \] \[ VI = \frac{1.5}{0.75} = 2 \text{ m} \]