What does the area under the hydrograph curve represent?

What does the area under the hydrograph curve represent?

• A. The peak discharge rate
• B. The rainfall depth over the period
• C. The volume of runoff
• D. The duration of a storm

Answer: (C)

The area under the hydrograph curve represents the total volume of runoff that flowed through the measurement point during the storm. A hydrograph plots discharge (a rate of flow) versus time, so integrating that discharge over the storm period gives how much water moved past the point. For example, if the discharge is 15 cubic meters per second for 2 hours, the area is 15 m^3/s × 7200 s = 108,000 m^3 of runoff. If you know the watershed area, you can convert that volume to a runoff depth by dividing by the watershed area. The peak discharge is simply the highest value on the curve, not the area, and rainfall depth or storm duration are not represented by the area alone.

The area under the hydrograph curve represents the total volume of runoff that flowed through the measurement point during the storm. A hydrograph plots discharge (a rate of flow) versus time, so integrating that discharge over the storm period gives how much water moved past the point. For example, if the discharge is 15 cubic meters per second for 2 hours, the area is 15 m^3/s × 7200 s = 108,000 m^3 of runoff. If you know the watershed area, you can convert that volume to a runoff depth by dividing by the watershed area. The peak discharge is simply the highest value on the curve, not the area, and rainfall depth or storm duration are not represented by the area alone.