1. Infiltration

3. 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

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

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

6. Moisture Zones during Infiltration
Infiltration Process
Moisture Zones during Infiltration

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

8. 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

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

10. 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.

11. Infiltration Measurement
Infiltrometer:

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

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

14. 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

15. 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

16. Estimation of Infiltration Rate
Horton’s Equation

17. Estimation of Infiltration Rate

18. 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.

19. 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

20. 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.