Question

When a portion of rainfall does not infiltrate into the soil and becomes surface runoff, it is called as

• A. Base flow
• B. Overland flow
• C. Cover flow
• D. Inter flow

Hint:

• Overland flow (also known as Horton overland flow or infiltration-excess overland flow) occurs when rainfall intensity exceeds the soil's infiltration capacity, or when the soil is saturated. This water flows over the land surface.
• Baseflow is groundwater contribution to streams.
• Interflow is shallow subsurface flow.
• Overland flow is a rapid component of surface runoff.

Answer 1

The Correct Option is B

When rainfall occurs, several things can happen to the water:

• Infiltration: Water soaks into the soil surface.
• Interception: Water is caught by vegetation.
• Surface Storage/Detention: Water accumulates in puddles or depressions on the surface.
• Surface Runoff: If the rainfall rate exceeds the infiltration capacity of the soil, or if the soil becomes saturated, excess water begins to flow over the land surface.

Let's examine the options:

• Overland Flow (option b): This is the term used to describe the movement of water over the land surface, typically as a thin sheet or in small rills and channels, before it reaches a larger stream or river. It occurs when precipitation rate exceeds infiltration capacity or when the soil is saturated. This directly matches the description in the question. It is a component of surface runoff.
• Baseflow (option a): This is the portion of streamflow that comes from groundwater seeping into the stream channel. It is a slower, more sustained flow and is not direct surface runoff from a rainfall event.
• Cover flow (option c): This is not a standard hydrological term in this context.
• Interflow (Subsurface Stormflow) (option d): This is the lateral movement of water within the unsaturated zone (vadose zone) or shallow saturated layers of the soil, above the main groundwater table. It eventually emerges at the surface or seeps into stream channels. It is faster than baseflow but slower than overland flow.

The question describes water that "does not infiltrate into the soil and becomes surface runoff." This is best described as overland flow. \[ \boxed{\text{Overland flow}} \]