The infiltration index that represents a constant average infiltration rate during a rainfall event is called
- AW-index
- Bφ-indexCorrect
- CHorton index
- DDarcy index
Solution
Concept
Constant average infiltration rate index
Formula
NONE
Step-by-step solution
1. An infiltration index converts a complex infiltration curve into an equivalent average infiltration rate. 2. The W-index represents the average infiltration rate during the period of rainfall excess. 3. Therefore, the constant average infiltration rate index is called the W-index. Answer: B
Explanation
The φ-index (φ-index) is defined as that constant rate of infiltration such that the volume of rainfall in excess of this rate equals the total direct runoff volume. It simplifies variable infiltration during a storm event into a single average rate. Therefore, option B is correct.
Why the other options are wrong
C) The Horton index represents an exponential decay model of infiltration capacity over time. D) Darcy's law relates to groundwater flow through porous media, not a rainfall infiltration index.
Shortcut
Phi-index (φ-index) is the constant average infiltration rate during rainfall excess.
Common mistake
Confusing the φ-index with the W-index, which accounts for initial losses and retention in addition to average infiltration rate.
Correct answer: B) φ-index