INFILTRATION

INFILTRATIONSAN ANTONIO, ANGELA MAE A.BSCE IV-AINFILTRATIONwater entering the soil at the ground surfaceIt replenishes the soil moisture deficiency and the excess moves downward by the force of gravity called deep seepage or percolation and builds up the ground water table.a surface process by which water on the ground surface enters thesoil. However, some of the infiltration does not go down and become groundwater and it simply makes the ground wet

The maximum rate at which the soil at any given condition is capable of absorbing water is called its infiltration capacity (fp).Infiltration (f) often begins at a high rate (20-25 cm/hr) and decreases to a fairly steady state rate (fc) as the rain continues, called the ultimate capacity(fp = 1.25 to 2.0 cm/hr).

The infiltration rate (f) at any time t is given by the Hortons equation.

INFILTRATION CURVE (HORTON)

As water moves in, air must either escape, or be compressed below the infiltrating water. Generally air escapes through larger pores, which slows the infiltration. Sometimes you see bubbles in puddles while its raining.If the precipitation rate exceeds the infiltration rate,runoffwill usually occur unless there is some physical barrier. It is related to the saturatedhydraulic conductivityof the near-surface soil.

The rate of infiltration can be measured using an infiltrometer.

Infiltration rateinsoil scienceis a measure of the rate at which soil is able to absorbrainfallorirrigation. It is measured in inches per hour or millimeters per hour. The rate decreases as the soil becomes saturated.In dry soil, water infiltrates rapidly. This is called theinitial infiltrationrate. As more water replaces the air in the pores, the water from the soil surface infiltrates more slowly and eventually reaches a steady rate. This is called the basicinfiltration rate.The infiltration rate depends on soil texture (the size of the soil particles) and soil structure (the arrangement of the soil particles): and is a useful way of categorizing soils from an irrigation point of view.PROCESS OF INFILTRATIONThe process of infiltration can continue only if there is room available for additional water at the soil surface. The available volume for additional water in the soil depends on the porosity of the soiland the rate at which previously infiltrated water can move away from the surface through the soil. The maximum rate that water can enter a soil in a given condition is the infiltration capacity. If the arrival of the water at the soil surface is less than the infiltration capacity, is sometimes analyzed usinghydrology transport models, mathematicsl models that consider infiltration, runoff and channel flow to predict river flow rates and streamwater quality.

IMPORTANCE OF INFILTRATION:

Soil water recharge (e.g., for plants)Groundwater rechargeRiver baseflowErosion (water that doesnt infiltrate runs off)FloodingContaminant movement

FACTORS AFFECTING INFILTRATIONPrecipitationThe greatest factor controlling infiltration is the amount and characteristics (intensity, duration, etc.) of precipitation that falls as rain or snow. Precipitation that infiltrates into the ground often seeps into streambeds over an extended period of time, thus a stream will often continue to flow when it hasn't rained for a long time and where there is no direct runoff from recent precipitation.

Soil characteristicsSome soils, such as clays, absorb less water at a slower rate than sandy soils. Soils absorbing less water result in more runoff overland into streams.

Soil saturationLike a wet sponge, soil already saturated from previous rainfall can't absorb much more ... thus more rainfall will becomesurface runoff.

Land coverSome land covers have a great impact on infiltration and rainfall runoff. Vegetation can slow the movement of runoff, allowing more time for it to seep into the ground. Impervious surfaces, such as parking lots, roads, and developments, act as a "fast lane" for rainfall - right into storm drains that drain directly into streams. Agriculture and the tillage of land also changes the infiltration patterns of a landscape. Water that, in natural conditions, infiltrated directly into soil now runs off into streams.

EvapotranspirationSome infiltration stays near the land surface, which is where plants put down their roots. Plants need this shallow groundwater to grow, and, by the process ofevapotranspiration, water is moved back into the atmosphereSlope of the landWater falling on steeply-sloped land runs off more quickly and infiltrates less than water falling on flat land.

INSTRUMENTS FOR MEASURING INFILTRATIONDouble ring infiltrometer The double ring infiltrometer is a simple instrument that is used to determine the rate of infiltration of water into the soil.The rate of infiltration is determined as the amount of water per surface area and time unit, that penetrates the soil. This rate can be calculated on the basis of the measuring results and the Law of Darcy.

The two rings (22.5 to 90 cm diameter) are driven into the ground by a driving plate and hammer, to penetrate into the soil uniformly without tilt or undue disturbance of the soil surface to a depth of 15 cm. After driving is over, any disturbed soil adjacent to the sides tamped with a metal tamper. Point gauges are fixed in the center of the rings and in the annular space between the two rings.

193.Water is poured into the rings to maintain the desired depth (2.5 to 15 cm with a minimum of 5mm) and the water added to maintain the original constant depth at regular time intervals (after the commencement of the experiment) of 5, 10, 20, 30, 40, 60 min, etc. up to a period of at least 6 hours is noted and the results are plotted as infiltration rate in cm/hr. versus time in minutes.

The purpose of the outer tube is to eliminate to some extent the edge effect of the surrounding drier soil and to prevent the water within the inner space from spreading over a larger area after penetrating below the bottom of the ring.

Thank YouPrepared by:San Antonio, Angela Mae A.BSCE IV-A