Question

Explain the types of run-off.

Answer 1

Based on the time interval between the instance of rainfall and generation of runoff, the runoff may be classified into the following three types.

• Surface Runoff:
  It is the portion of rainfall, which enters the stream immediately after the rainfall. It occurs, when the rainfall is longer, heavier, and exceeds the rate of infiltration. In this condition, the excess water makes ahead over the ground surface, which tends to move from one place to another following a land gradient and is known as overland flow. When the overland flow joins the streams, channels, or oceans, it is termed as surface runoff or surface flow.
  
• Sub – Surface Runoff:
  The water that has entered the subsoil and moves laterally without joining the water-table to the streams, rivers, or oceans is known as sub-surface runoff. The subsurface runoff is usually referred to as interflow.
• Base Flow:
  It is a flow of underground water from a saturated ground water zone to a water channel. It usually appears at a downstream location where the channel elevation is lower than the groundwater table. Groundwater provides the stream flow during dry periods of small or no precipitation.