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SURFACE AND SUBSURFACE RUNOFF PHENOMENON

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Alyssa Agra

on 1 February 2016

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Transcript of SURFACE AND SUBSURFACE RUNOFF PHENOMENON

SURFACE AND SUBSURFACE RUNOFF PHENOMENON
WHAT IS RUNOFF?

the portion of rainfall, snowmelt, and/or irrigation water that runs over the soil surface toward the stream rather than infiltrating into the soil-- sometimes called surface runoff
"Runoff" is sometimes used to refer to both surface runoff (overland flow) and subsurface runoff (interflow).
What's the difference between the two?
There are two types of surface runoff that occur during rainfall or snowmelt.
Surface runoff is water from rain, snow melting, or other sources that flows over the land surface, and is a major component of the water cycle.
Interflow, also known as subsurface runoff is relatively rapid flow toward the stream channel that occurs below the surface. It occurs more rapidly than baseflow, but typically more slowly than surface runoff.
SURFACE RUNOFF PHENOMENON
ROLE IN FLOOD PREDICTION
Once we know the amount of water expected to become runoff, other tools such as the unit hydrograph can assist us with estimating the resulting discharge in the stream.
ENTRY- TRANSMISSION - STORAGE
GENERAL RUNOFF TERMS
or base runoff, is the long-term supply of water that keeps at least some water in the stream even during extended dry periods. Baseflow comes from water that percolated down into deep storage.
BASEFLOW
INFILTRATION is the downward movement of water through the soil surface. While it is often used interchangeably with percolation,
PERCOLATION actually refers to movement of water within soil, and infiltration specifically refers just to the process of water entering a soil surface.
INFILTRATION RATE is the amount of water able to enter the soil in a specified time period. It is expressed as depth per time; for example, 10 millimeters per hour.

SATURATION EXCESS FLOW
is the upper limit of infiltration rate. It includes surface infiltration and percolation and is expressed in depth per time; for example, 15 millimeters per hour.

If precipitation rate is less than or equal to infiltration capacity, no surface runoff occurs.

INFILTRATION CAPACITY
THE FOLLOWING INFLUENCES RUNOFF :
BASIC SLOPE
ROUGHNESS
STREAM DENSITY
URBANIZATION
SOIL PROPERTIES
SOIL TEXTURE CLASSIFICATION
SOIL COMPOSITION
SOIL PROFILE
SURFACE PROPERTIES
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