Question

Consider the following steps which are involved in arriving at a unit hydrograph:
1. Separation of base flow
2. Estimating the surface runoff in volume
3. Estimating the surface runoff in depth
4. Dividing surface runoff ordinate by depth of runoff
Which is the correct sequence of these steps?

• A. 4, 3, 2 and 1
• B. 1, 2, 3 and 4
• C. 4, 2, 3 and 1
• D. 1, 3, 2 and 4

Answer 1

The correct option is B 1, 2, 3 and 4

• The separation of base flow gives Direct Runoff Hydrograph (DRH)
• The area under the DRH gives volume of surface runoff.
• The effective depth of precipitation can be obtained by using index or volume of surface runoff divided by the catchment area.
• Finally the ordinates of UH can be obtained by dividing the ordinates or DRH by effective depth of precipitation.