Infiltration Introduction

3.1 What is the infiltration?

                                Infiltration is a flow of water through the soil surface.
Infiltration effects to runoff, transpiration, and evaporation. 

Infiltration capacity- With time, infiltration is decreased and infiltration capacity has remained constant. Pores in the soil are less filled with water before precipitation. When precipitation has occurred, pores are getting to fill water. After saturation of all pores in the soil, water cannot be absorbed anymore, therefore, infiltration capacity has become constant.

3.2 Factors affecting infiltration

(1) Rainfall

-Intensity (When infiltration capacity is higher than rainfall capacity, all the rain is infiltrated. When rainfall intensity is higher than infiltration capacity, infiltration is less and runoff has occurred.)

-Duration (Duration of rainfall is high, infiltration is less and runoff has occurred after a few hours.)

(2) Climate

-When the temperature is relatively high, the rate of microbial activities is high.  Therefore relatively more amount of organic matter is added to soil surface cover so soil particles are well aggregated so the size of pores is large and infiltration capacity is relatively high.

(3) Soil characters

                  -Soil type(Light color soils such as sandy soils have relatively larger infiltration capacity than heavy soils such as clay soils because sandy soils have relatively larger pores that are well connected together than clay soils.)

               

-Compaction(Compacted soils have relatively lower infiltration capacity than loose soils because of size and amount of pores in compacted soil is relatively very small therefore compacted soils have less infiltration capacity.)

                  -Sun cracks (When soils contain sun cracks, these soils have relatively larger infiltration capacity because soils are so dry and have relatively lowest amount of water.  Therefore infiltration capacity is relatively high.

                      -Depth to storage (When depth between the surface and storage is relatively high, infiltration capacity is high                      because of amount of pores are increased with increasing of depth, therefore, more water is needed to saturated for pores, therefore, infiltration capacity is relatively high.)

                      -Soil moisture (When soil have relatively less moisture content, soils can absorb more water, therefore, infiltration capacity is relatively high. High moist soils can absorb relatively less amount of water, therefore, infiltration capacity is restively low.)

                      -Soil slope(Steep slopes have relatively less infiltration capacity because of water flows rapidly so water is not retained for a long period so soils can absorb more water, therefore, infiltration capacity is relatively less. Gentle slope have relatively high infiltration capacity because the water flows slowly so water retain in surface relatively long-time period so soils can absorb more water therefore infiltration capacity is restively high.)

(4) Cultivation practices

                        -Closely growing vegetation (Soils are less compacted so infiltration capacity is high)

                        -Land preparation (Surface roughness is increased in land preparation practices  so infiltration capacity become high)

(5) Surface cover

                         -Vegetation cover type (When land has row crops vegetation, most of the land are uncovered of vegetation. Therefore soils are relatively more compacted and consist of low amount of organic matter, therefore, soils have relatively less infiltration capacity.)

                         -Organic matter on the surface (When organic matter is relatively high on the surface, infiltration capacity is high because organic matter can hold a large amount of water and allows movement toward soil)

                         -Urban paving(Most of the soils in cities are covered by artificial instructions so these soils are avoided to absorb water by these artificial layers so infiltration capacity is relatively low in cities.

                 3.3 Computing of Infiltration

Kostiakov’s equation

                                                                               

I = Cumulative depth of infiltration

t = time

k and n are constants

                                     

                   

i = infiltration rate

3.4 Measurement of infiltration

Double ring infiltrometer 

The surface vegetation is cleaned without disrobing soil surface.

Rings are put into 15cm.

A plastic / polythene sheet is put inner ring and filled water for particular depth.

Water is poured into the outer ring and allowed it to infiltrate.

The plastic sheets are removed from inner rings and start recording depth with time