What is the unit area hydrograph used for in design and planning?

What is the unit area hydrograph used for in design and planning?

• A. The hydrograph for 1 unit area; used to estimate runoff for other basins.
• B. A graph of rainfall intensity over time.
• C. A plot of groundwater head over time.
• D. A graph of soil moisture vs time.

Answer: (B)

The unit area hydrograph is a discharge response that shows how a watershed would produce runoff when a uniform unit depth of rainfall excess is added over the entire basin for a given duration, and it is expressed per unit area. This provides a transferable response function: by scaling for the actual basin area and the amount of rainfall, you can estimate the runoff hydrograph for different storms or different basins without starting from scratch. In design and planning, engineers use this to predict peak discharge and the overall shape of the runoff hydrograph by convolving the unit hydrograph with the rainfall excess hyetograph of the storm. It’s not a rainfall intensity curve, nor a groundwater head plot, nor a soil moisture plot.

The unit area hydrograph is a discharge response that shows how a watershed would produce runoff when a uniform unit depth of rainfall excess is added over the entire basin for a given duration, and it is expressed per unit area. This provides a transferable response function: by scaling for the actual basin area and the amount of rainfall, you can estimate the runoff hydrograph for different storms or different basins without starting from scratch. In design and planning, engineers use this to predict peak discharge and the overall shape of the runoff hydrograph by convolving the unit hydrograph with the rainfall excess hyetograph of the storm. It’s not a rainfall intensity curve, nor a groundwater head plot, nor a soil moisture plot.