Question

The intensity of rainfall for a 2-hour unit hydrograph is:

• A. 2.0 cm/h
• B. 1.0 cm/h
• C. 0.25 cm/h
• D. 0.5 cm/h

Hint:

The key to unit hydrograph problems is the definition: 1 cm of effective rainfall over the specified 'D' duration. The intensity is simply \( 1/D \). For an instantaneous unit hydrograph (IUH), the duration is assumed to be zero, leading to an infinite intensity represented by a Dirac delta function.

Answer 1

The Correct Option is D

Step 1: Define a unit hydrograph. A unit hydrograph is defined as the direct runoff hydrograph resulting from 1 cm of effective rainfall (rainfall excess) generated uniformly over a watershed at a constant rate for a specified duration, known as the unit duration.
Step 2: Calculate the rainfall intensity. In this problem, the total depth of effective rainfall is 1 cm, and the duration over which this rainfall occurs is 2 hours.
The intensity of rainfall is the total depth divided by the duration. \[ \text{Intensity} = \frac{\text{Total Depth of Rainfall}}{\text{Duration}} \] \[ \text{Intensity} = \frac{1 \text{ cm}}{2 \text{ hours}} = 0.5 \text{ cm/h} \]