Infiltration

Infiltration Process Infiltration : Process of water entry into the soil through the soil surface When water is ponded on a homogeneous soil, characteristic zones of saturation, water transmission, and soil wetting, develop as the wetting front propagates downward

It is a process of water penetrating from the ground surface into the ground Definition

Infiltration Process Infiltration Capacity Infiltration Rate Maximum rate water is absorbed by the soil Infiltration Rate Infiltration occurring at less than capacity

Moisture Zones during Infiltration Infiltration Process Moisture Zones during Infiltration

Infiltration Process The factors affecting infiltration are: 1) precipitation. 2) soil types. 3) water contents in the soil. 4) vegetation cover. 5) ground slope.

Infiltration Process Effect of soil types It is measured in inches per hour or millimeters per hour. The rate decreases as the soil becomes saturated. If the precipitation rate exceeds the infiltration rate, runoff will usually occur

Measurement Of Infiltration 3 methods to determine infiltration rate Flooding infiltrometer Rainfall simulator Hydrograph analysis

Infiltration Measurement Infiltrometer: Infiltrometer is a device used to measure the rate of water infiltration into soil or other porous media. Commonly used infiltrometers are single ring or double ring infiltrometer. It is easy to use, but soil structure could be disturbed.

Infiltration Measurement Infiltrometer:

Infiltration Measurement Artificial rain simulation No disturbance to soil, close to true rainfall impact, but high cost.

Method to calculate infiltration Horton’s Equation Phillip’s Equation

Horton’s equation f(t) = fc + (f0 – fc) e-kt Infiltration start at rate f0 and exponentially decreases until it reaches constent rate fc k = delay constant f0 = initial infiltration fc = constant infiltration f(t) = infiltration rate

Phillip’s equation F(t) = St1/2 + Kt Where S is a parameter called sorptivity, which is a function of the soil suction potential, and K is the hydraulic conductivity By differentiation f(t) = ½ St-1/2 + K

Estimation of Infiltration Rate Horton’s Equation

Estimation of Infiltration Rate

Rain that fall in watershed will flow on the ground, into river and discharged out downstream. Some of the water will infiltrate into ground and this reduce surface runoff. In soil in watershed is mostly sand, infiltration rate will be high and surface runoff will be low. This allow us to make optimum design of drainage facilities Example: how big and wider river need to be Allowable obstruction to water flow by briges.

Estimation of Infiltration Rate Ex1: The initial infiltration capacity fo of a catchment is estimated as 4.5 mm/hr, the time constant as 0.35 /hour, and capacity fc as 0.4 mm/hour. Apply Horton's equation to find the following: a) The value ft at t=10 min, 30 min, 1 hr, 2 hr and 6 hr. b) The total volume of infiltration over the 6 hours period. Assume continuously ponded conditions

EX:2 Suppose that the parameters for Horton’s equation are fo=3 EX:2 Suppose that the parameters for Horton’s equation are fo=3.5mm/hr, fc=0.6 mm/hr and k=4.1 hr-1. Determine the infiltration rates after 0, 10 min, 20 min, 1 hr, 1.5 hr and 2 hr and the cumulative infiltration after 2 hours. Assume continuously ponded conditions.