31.4. Selection of Appropriate Index

Try these first

1. 1.

   What index should be used if both rainfall and runoff data are available?

   Hint

   Think about which index relies directly on runoff and rainfall data.

2. 2.

   Name an infiltration index that considers initial losses.

   Hint

   Remember the index that modifies the φ-index for accurate infiltration measures.

3. 3.

   Which index is easier to apply if both runoff and rainfall data are available?

   • φ-index
   • W-index
   • W min-index

   Hint

   Think about which index does not require additional information.

4. 4.

   True or False: The W-index includes initial losses in its calculation.

   • True
   • False

   Hint

   Recall what adjustments the W-index makes compared to the φ-index.

5. 5.

   A study area in an urban environment has recorded a total rainfall of 100 mm with a direct runoff of 60 mm. If initial losses are estimated to be 15 mm, calculate both the φ-index and W-index.

   Hint

   Ensure you understand the formulas for both indices and remember to define `t`.

6. 6.

   Given a short-duration storm produces heavy runoff in a basin with mixed soils, discuss why the selection of the W min-index is critical for runoff assessment in this situation. What would the consequences be of using the φ-index instead?

   Hint

   Think about how each index responds differently to storm events.