In a basin with large size and gentle slope, lag time is typically:

In a basin with large size and gentle slope, lag time is typically:

• A. Shorter
• B. Longer
• C. The same regardless of conditions
• D. Not predictable

Answer: (B)

Lag time is the delay between the rainfall peak and the runoff peak at the basin outlet. In a basin that is large and has a gentle slope, water has to travel longer distances through the river network and more time is spent draining and storing water in soils, groundwater, wetlands, and other storage features. The gentler slope slows the movement of overland flow and streamflow, reducing peak velocities. All of this spreads out the runoff over a longer period, pushing the outlet peak further in time. So the overall delay between rainfall and peak discharge is longer in such basins. The other scenarios—smaller or steeper basins producing a quicker, flashier response, or the idea that lag time is unchanged or not predictable—do not align with how larger, storage-rich, and slow-moving basins delay runoff.

Lag time is the delay between the rainfall peak and the runoff peak at the basin outlet. In a basin that is large and has a gentle slope, water has to travel longer distances through the river network and more time is spent draining and storing water in soils, groundwater, wetlands, and other storage features. The gentler slope slows the movement of overland flow and streamflow, reducing peak velocities. All of this spreads out the runoff over a longer period, pushing the outlet peak further in time. So the overall delay between rainfall and peak discharge is longer in such basins. The other scenarios—smaller or steeper basins producing a quicker, flashier response, or the idea that lag time is unchanged or not predictable—do not align with how larger, storage-rich, and slow-moving basins delay runoff.