31.2. Need for Infiltration Indices

Try these first

1. 1.

   Define infiltration in your own words.

   Hint

   Think about what happens when it rains.

2. 2.

   What is the purpose of infiltration indices?

   Hint

   Consider how they relate to runoff.

3. 3.

   What do infiltration indices help estimate?

   • Total Rainfall
   • Storm Duration
   • Effective Rainfall

   Hint

   Focus on the purpose of these indices.

4. 4.

   T/F: The φ-index considers initial abstraction losses.

   • True
   • False

   Hint

   Think about the definitions of both indices.

5. 5.

   In a region where the average rainfall is 80 mm during a storm, and through analysis it’s determined that 30 mm runoff occurs and 15 mm in initial losses, calculate the W-index for a storm of 2 hours duration.

   Hint

   Make sure you plug in the right numbers for P, Q, and I.

6. 6.

   Discuss the conditions under which infiltration indices become less effective in predicting runoff.

   Hint

   Consider the assumptions made when deriving the indices.