31.3.1. φ-index (Phi Index)

Try these first

1. 1.

   What does the φ-index represent?

   Hint

   Think about how rainfall and runoff relate to each other.

2. 2.

   Calculate the φ-index if total rainfall is 80 mm and direct runoff is 20 mm over a 2-hour storm.

   Hint

   Use the formula φ = (P - Q) / t.

3. 3.

   What does the φ-index measure?

   • Average infiltration rate
   • Total rainfall
   • Runoff volume

   Hint

   Think about what you're measuring during a storm event.

4. 4.

   The φ-index assumes which of the following?

   • True
   • False

   Hint

   Consider the definitions provided in class.

5. 5.

   Over a course of a 6-hour storm, 200 mm of rainfall occurred, with 80 mm directly running off into a stream. Calculate the φ-index and discuss the implication of initial loss neglect.

   Hint

   Review your calculations carefully, especially the assumptions.

6. 6.

   Analyze and critique the φ-index from a sustainability perspective in urban environments prone to heavy rains. What might be some long-term implications?

   Hint

   Reflect on both environmental sustainability and practical applications.