Question

The peak rate of runoff can be estimated using the

• A. Soil conservation service method
• B. Rational formula
• C. Blaney-Criddle Method
• D. Penman method

Hint:

Remember the metric version of the Rational Formula:
\[ Q = \frac{C \cdot I \cdot A}{360} \]
This constant $360$ is a conversion factor that converts area in hectares and intensity in mm/hr directly into discharge in cubic meters per second ($\text{m}^3/\text{s}$).

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Estimating the peak rate of runoff is essential for designing soil conservation structures, drainage systems, culverts, and spillways.
Various empirical and conceptual models are used based on the size and characteristics of the watershed.
Key Formula or Approach:
The peak runoff rate is commonly calculated using the Rational Formula:
\[ Q_p = \frac{C \cdot I \cdot A}{360} \]
where $Q_p$ is the peak runoff rate ($\text{m}^3/\text{s}$), $C$ is the dimensionless runoff coefficient, $I$ is the rainfall intensity ($\text{mm/hr}$), and $A$ is the drainage area ($\text{ha}$).

Step 2: Detailed Explanation:
The ______Rational formula______ is the most widely used empirical relationship for estimating peak runoff rates from small agricultural and urban watersheds (typically less than $50\,\text{km}^2$).
It assumes that the maximum rate of runoff occurs when the entire watershed is contributing, which happens when the rainfall duration equals or exceeds the time of concentration of the watershed.
Let us evaluate the other options:
- The Soil Conservation Service (SCS) Curve Number method is typically used to estimate total runoff volume rather than directly estimating peak rate, although it can be extended.
- The Blaney-Criddle and Penman methods are used exclusively to calculate potential evapotranspiration and crop water requirements, and have no application in runoff estimation.

Step 3: Final Answer:
The peak rate of runoff is estimated using the Rational formula, which corresponds to option (B).