Section 4: Soil and Water Conservation Engineering
Soil and Water Erosion
Subtopic: Gully control structures – drop, drop inlet and chute spillways
Question Statement:
In a straight drop spillway stilling basin, the drop height $Y = 2.5\text{ m}$ and critical depth $y_c = 0.80\text{ m}$. The drop number $D_n = \frac{q^2}{g Y^3} = \left(\frac{y_c}{Y}\right)^3$. The value of the drop number $D_n$ is ________ (round off to 4 decimal places).
Answer Key:
0.0328
Step-by-Step Solution & Explanation
Drop number definition:
$D_n = \left(\frac{y_c}{Y}\right)^3$
Given $y_c = 0.80\text{ m}$ and $Y = 2.5\text{ m}$:
$\frac{y_c}{Y} = \frac{0.80}{2.50} = 0.32$
$D_n = (0.32)^3 = 0.032768 \approx 0.0328$