Infiltration

Infiltration refers to the flow of water into the ground through the soil surface. The infiltrated water is used in increasing the moisture content of soil up to field capacity and extra water goes down which becomes ground water. On the other hand, percolation is the process of water flow from one point to another within the soil. It is the zone of aeration towards the water table. Both infiltration and percolation play a key role in surface runoff, groundwater discharge, evapotranspiration, soil erosion, and transport of chemicals in surface and subsurface waters.

what is infiltration?

When water is applied at the surface of the soil, four moisture zones can be identified, which are as follows:

Saturation zone
Transition zone
Transmission zone
Wetting zone

infiltration capacity

The infiltration capacity of a given catchment area depends on the following characteristics:

Soil Characteristics
Condition of the soil surface
Vegetative cover
Current moisture content
Soil temperature

measurements of infiltration

The infiltration characteristics of soil can be estimated using the following measurements:

Using flooding type infiltrometers
Measurement of subsidence of free water in a large basin or pond
Rainfall simulator
Hydrograph analysis

horton's model and phillip equation

horton's equation

Horton's Equation is a viable option used when measuring ground infiltration rates or volumes. It expresses the decay of infiltration capacity with time as an exponential given by the equation provided. It can also be used to find the total volume of infiltration F over some time t .

sample problems:

philip's equation

Philip's equation is a power series equation developed by Philips (1957) which explains the initial stages of infiltration (as explained in the first equation model) and the gravity component, which is represented in the second term of the equation
It can be applied for a constant head boundary condition and falling head infiltration
It relates the most known equation in hydrology such as Darcy's Law, Darcy-Buckingham Law and Richard's Equation
It is used to determine the cumulative infiltration and infiltration rate (derived from cumulative infiltration).

sample problems

green ampt model

Green-Ampt model is an infiltration model developed from a theory by Green and Ampt to form an exact solution. This method is used to derive an equation for computing the total depth of infiltration
Shown in the right figure are the key terms and symbols used, the Green-Ampt equation and its parameters.

sample problems

ponding time

Ponding time refers to the instance when the land surface becomes saturated due to rain, which results to the ponding of water. It is defined as the elapsed time between initial time rainfall and the time where water begins to pond on the soil surface.
Ponding time can be solved using the equation provided as shown:

sample problems

FITTING INFILTRATION MODELS TO INFILTRATION DATA USING EXCEL

Various infiltration models can be used and represented using excel software. It is considerably an effective tool for estimating the infiltration parameters in a more precise manner. Using the graphical representation of infiltration models via excel will lucidly present infiltration data obtained.
Infiltration models such as in Horton and Philips Equation, Green-Ampt Equation, and Ponding Time can be graphically presented in excel to which is essential in analyzing the infiltration depth, cumulative infiltration and infiltration rate, time of ponding, and their correlations with the rainfall intensity.

assessment tasks:

PROBLEM SET #2

Infiltration_Bartolome.pdf

QUIZ #2

HYDROLOGY_ Infiltration.pdf

VIDEO PRESENTATION LINK: https://youtu.be/Q9smOfq90Uk

reflection:

Infiltration pertains to the downward movement of water into the soil surface. Soil serves as a reservoir for water storage, which can be used for plant growth. Otherwise, water through capillary strength will percolate underground. It is crucially important to understand the aspects and factors contributing to infiltration for it is highly related to geological processes such as soil erosion and gully formation. Thus, when poorly managed by human manipulation and intervention of hydrological processes, infiltration rates will be limited, resulting in insufficient water supply underground. Thus, weakened soil structure will induce the chance of overland flows to occur, which can cause disastrous events like excessive floods, eroded streambanks, and collapsing of roads and other pavements.

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