Infiltration and Percolation – Detailed Note
The passage of liquid water through the soil surface is termed as infiltration
The passage of liquid water through the soil profile is called percolation.
Infiltration Capacity: –
The maximum rate at which water under given conditions, can enter the soil through the surface is called infiltration capacity.
Percolation Capacity: –
It is defined as the rate at which water penetrates through the soil profile.
Factors affecting Runoff, Infiltration and Percolation
By increasing infiltration the percolation also increases while the runoff decreases. So factors, which increase infiltration, are the factors of a decrease in runoff and vice some of these factors are:
The initial moisture content of the soil: –
- The lower is the initial moisture content of the soil the faster will be the rate of infiltration capacity and decreases runoff.
Rainfall intensity & duration: –
- Long duration with the slow intensity of rainfall will contribute more water for infiltration process and less runoff than for short duration and high intensity.
The texture of soil: –
- Small particles offer greater resistance to water movement than larger particles as in smaller particles water is subjected to greater friction. Sandy soil, therefore, has a high infiltration capacity than of a fine texture clay soils, and have less runoff.
Structure of the Soils: –
- It soil particles combine to form soil aggregates, the total free spaces of a given volume soil increases and in general, the infiltration capacity will be greater. .It is for this reason that well-aggregated soil has more infiltration capacity but less runoff.
Organic Substances: –
- The addition of organic material to soil greatly improves its aggregate structure and increase porosity and infiltration capacity while decreasing the runoff.
- It is evident that soil on steep slopes has a lower infiltration capacity and greater runoff than the soil under level conditions, as the water has more time to infiltrate.
Season effects: –
- In hot weather condition where evapotranspiration rate is high, emptier pore spaces of soil are available for the infiltrative water; hence infiltrating capacity will be more and less runoff than in wet and cold season condition.
The viscosity of water: –
- The contaminated water when enters the soil will have to face more turbulence effects rather than clean water. It can be stated the condition of the viscosity of water will lower the infiltration capacity.
The degree of soil freezing: –
- The presence of cracks which have been occurred due to expansion & contraction of surface soil will increase infiltration capacity and decrease runoff.
Cracks in the soil: –
- The presence of cracks which have been occurred due to expansion & contraction of surface soil will increase infiltration capacity and decreases runoff.
- Vegetation has remarkable effects to increase the infiltration capacity of soil with its interception, fallen leaves, and litters present on the surface of the watershed and decrease the velocity of flowing water as well as increase the porosity of soils with humus formation. So vegetation increases infiltration and decreases runoff.
Animal effect: –
- The presence of rodents i-e rates, rabbits, porcupine earthworm, ants, and termites increase the porosity of soils and in response to that infiltration capacity will be more and runoff will be less.
The form of precipitation: –
- Soil form of ppt (snow) will increase the infiltration & decrease the runoff.
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