﻿ Infiltration (hydrology)

# Infiltration (hydrology)

Infiltration is the process of penetration of rain into the earth; he is an important part of the process of the water cycle. Port processes can be groundwater recharge and runoff generation. The infiltration rate is measured with the units millimeters per second or practical per minute.

## Introduction

The infiltration is significantly influenced by two forces of gravity and capillarity or the matric potential. Other key factors are the temperature in the soil, the water saturation of the soil ( antecedent soil moisture ), the degree of coverage ( vegetation ) and the rainfall intensity. So have sandy soils (63 microns to 2 mm grain size ), with relatively large, well- connected pores and large pore volume ( 30-45 % ) had the highest infiltration rates. As a vegetation cover attenuates the impact of raindrops, it effectively prevents the superficial silting up of pores and creates root through your network more additional, readily water- conducting macropores. Thus it has a significant positive influence on the infiltration characteristics of the soil (highest infiltration rates can be observed in forest soils ).

## Measurement

The measurement of the potential infiltration done by means of so-called infiltrometer. It usually is a ring with a defined cross -section which is inserted into the ground and is then filled up to a defined height also with water.

Because of the filling height and the ring diameter, the filled volume of water is known, the potential infiltration (infiltration at maximum available water ) over time may elapse before all the water seeps out of the ring is to be determined.

By the use of Doppelringinfiltrometern attempting to minimize a loss of lateral seepage of these would result in the measurement to higher infiltration rates. When double ring, only the internal volume is considered for measurement.

From

Follows according to Darcy's law:

With:

## Estimating the actual infiltration

### Estimation of the water balance

If all other parameters are known, the infiltration F can be calculated as the residual term of the water balance equation.

With:

Depending on the assessment of the local conditions, this equation can also be simplified by single elements.

### Green- Ampt infiltration model

The Green- Ampt infiltration model provides an estimate of the actual infiltration considering various soil parameters, as there would be: soil water potential, porosity, hydraulic conductivity and the soil parameters independent of time. The semi - physical formula approximates the infiltration process by a step profile with complete water saturation and the so-called transport zone. Only the Water-saturated part of the bottom is viewed (constant). The formula is derived from the Darcy -Weisbach equation, where the principle is based on the so-called gradient method. At the beginning affects a high soil water potential ( matric potential ), which is weaker with time.

With:

By integration of the equation can be solved by either the infiltration volume or after the initial infiltration rate.

### Model to Horton

The initial infiltration value applicable at the beginning of the infiltration process. With increasing duration reduces its impact and it adjusts itself to the end- infiltration value. The model describes an exponential decrease in the infiltration rate to the end infiltration rate at saturation of the soil.

With:

Similarly to the model according to Green and Ampt, also has a component of the model Horton describing the decrease in the rate of infiltration and takes into account the constant part. The infiltration rate is never 0 but approaches a final value which depends upon the gravitational potential. This final value would theoretically equal to the saturated hydraulic conductivity be which is used explicitly for at Green - Ampt ( for ). The model parameters are estimated for Horton in general, applies to non-vegetated sandy clay or grass for soil:

### Other models

Other commonly used models are:

Empirical model

With:

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