31.5. Estimation of Infiltration Indices from Hydrographs

Try these first

1. 1.

   What is a hydrograph?

   Hint

   Think about what it represents in terms of water flow.

2. 2.

   Why are initial losses important in the calculation of infiltration indices?

   Hint

   Consider what happens to the water before it infiltrates.

3. 3.

   What does the φ-index represent?

   • Initial losses
   • Average infiltration rate equating rainfall excess to runoff
   • Total runoff only

   Hint

   Recall the definition from our discussions.

4. 4.

   True or False: Initial losses must be considered when calculating W-index.

   • True
   • False

   Hint

   Think about the definition of W-index.

5. 5.

   You have rainfall data showing 100 mm over a 4-hour storm. The hydrograph indicates direct runoff of 70 mm, and initial losses are estimated at 25 mm. Calculate both the φ-index and W-index.

   Hint

   Break down the calculations step by step.

6. 6.

   Discuss the potential consequences of overlooking initial losses when estimating runoff in an urban drainage system.

   Hint

   Consider the role of initial conditions in runoff generation.