GOOD DECK Flashcards
is the process of water entry into a soil from rainfall, or irrigation.
INFILTRATION
Another word for soil water movement
PERCOLATION
is the process of water flow from one point to another point within the soil.
SOIL WATER MOVEMENT OR PERCOLATION
is the rate at which the water actually infiltrates through the soil during a storm and it must be equal the infiltration capacities or the rainfall rate, which ever is lesser.
INFILTRATION RATE
the maximum rate at which a soil in any given condition is capable of absorbing water
INFILTRATION CAPACITY
is primarily controlled by the rate of soil water movement below the surface and the soil water movement continues after an infiltration event, as the infiltrated water is redistributed.
THE RATE OF INFILTRATION
play a key role in surface runoff, groundwater recharge, evapotranspiration, soil erosion, and transport of chemicals in surface and subsurface waters.
INFILTRATION AND PERCOLATION
Infiltration rate is dependent on a few conditions namely,
Land surface
Land vegetation cover
Surface soil characteristics
Storm characteristics
Surface soil and water temperature,
Chemical properties of the water and soil
Soil properties affecting soil water movement…
Hydraulic conductivity
Water-retention characteristics
a measure of the soil’s ability to transmit water
Hydraulic conductivity
the ability of the soil to store and release water
Water-retention characteristics
is accomplished by analysis of rainfall-runoff data from a watershed.
Areal infiltration estimation
obtained by subtracting runoff volume from rainfall volume.
Infiltration volume
obtained by dividing infiltration volume by rainfall duration.
Average infiltration rate
what is integrated to calculate the total rainfall volume
Rainfall hyetograph
what is integrated to calculate runoff volume
Runoff hydrograph
2 measurements of infiltration
Areal measurement
Point Measurement
are normally made by applying water at a specific site to a finite area and measuring the intake of the soil
Point infiltration measurements
four types of infiltrometers
Ponded-water ring of cylinder type
Sprinkler type
Tension type
Furrow type
infiltrometers should be used to determine infiltration rates for inundated soils such as flood irrigation or pond seepage
Ring
infiltrometers should be used where the effect of rainfall on surface conditions influences the infiltration rate
Sprinkler
used to determine the infiltration rates of soil matrix in the presence of macropores.
Tension infiltrometers
are used when the effect of flowing water is important, as in furrow irrigation.
Furrow infiltrometers
are usually metal rings with a diameter of 30 to 100 cm and a height of 20 cm.
Ring infiltrometers
With the help of rain simulator, water is sprinkled at a uniform rate in excess of the infiltration capacity, over a certain experimental area.
Sprinkler infiltrometer
formula for infiltration f using sprinkler infiltrometers
f=(P-R)/t
P- Rain sprinkled
R- Runoff collected
t- duration of rainfall
Horton’s equation for INFILTRATION CAPACITY
fp=fc+(f0-fc)e^(-kt)
Horton’s equation for cumulative infiltration F(t)
F(t)= fct + ((fo-fc)(1-e^(-kt)))/k
Philip’s equation for cumulative infiltration F(t)
F(t)= St^(0.5)+Kt
Philip’s equation for infiltration rate f(t)
f(t)=0.5St^(-0.5)+K
the elapsed time between the time rainfall begins and the time water begins to pond on the soil surface.
Ponding time
is a conceptual model of infiltration of precipitation in an unsaturated flow
The Green and Ampt infiltration model
was originally derived using a simplification of the comprehensive Richard’s equation (1931) for unsteady water flow in soil and in Darcy’s Law.
. The Green and Ampt loss method
Five Principal Assumptions of the Green-Ampt Method
The soil under consideration is homogeneous and stable, implying that macropores and preferential migration pathways should not be considered.
The supply of ponded water at the surface is not limited.
A distinct and precise definable wetting front exists and as water cotinues to infiltrate, the wetting front advances at the same rate with depth.
The capillary suction just below wetting point is uniform throughout the profile and constant in time during the infiltartion event.
The soil is uniformly saturated above the wetting front, and the volumetric water contents remain constant above and below the advancing wetting front.
