31. Infiltration Indices

Try these first

1. 1.

   Define Infiltration Capacity.

   Hint

   Think about the 'max' rate of absorption.

2. 2.

   What does the φ-index represent?

   Hint

   Contains 'phi' & relates to average rates.

3. 3.

   What does the φ-index represent?

   • A constant infiltration rate during storms
   • Average rate of infiltration equating excess rainfall to runoff
   • Initial loss during infiltration

   Hint

   Focus on what φ relates to in terms of average performance.

4. 4.

   True or False: The W-index can calculate runoff even when initial losses are unknown.

   • True
   • False

   Hint

   Consider the role of initial conditions.

5. 5.

   Given a rainfall of 200 mm and a direct runoff of 80 mm over 4 hours, calculate the φ-index, and discuss how accurate this representation is under different conditions.

   Hint

   Focus on how rainfall duration impacts the infiltration capability.

6. 6.

   Provide a detailed plan for selecting between φ-index and W-index for a proposed urban drainage system, considering local conditions.

   Hint

   Think about local land cover, vegetation, and recent rainfall history.