|
1. Definition
|
Name
|
INFILTRATION
CAPACITY
|
|
Brief
definition
|
The
property of soil which determines the infiltration
rate of rain water.
|
|
Unit of measure
|
mm/hour
|
2.
Position within the logical framework DPSIR
|
Type
of Indicator
|
State.
It is an intrinsic characteristic of an index of soil
vulnerability to the splash of rain, to loss of sediment,
and to runoff.
|
3.
Target and political pertinence
|
Objective
|
Contribution
to the identification of environmentally sensitive
areas by assessing how soil fulfils the function of
storing water.
|
|
Importance
with respect to desertification
|
This
indicator is part of a set of tools to identify and
mitigate land degradation, developed in the MEDALUS
target area of the Alentejo, Portugal. Together with
the indicators of soil surface stability and data
relative to the occurrence of extreme rain events,
it contributes to assessing the vulnerability of land
itself and consequently to the elaboration of development
strategies compatible with the resources available
in a given area.
|
|
International
Conventions and agreements
|
The
UNCCD emphasizes the fact that combating desertification
must be tackled within the general framework of actions
to promote sustainable development.
Within
Agenda 21 infiltration capacity is relevant to Chapter
12 - Management of fragile ecosystems: combating desertification
and drought.
|
|
Secondary objectives
of the indicator
|
|
4.
Methodological description and basic definitions
|
Definitions
and basic concepts
|
The
indicator defines the soil property on which the speed
of rain water infiltration depends.
|
|
Benchmarks
Indication of the values/ranges of value
|
|
|
Methods
of measurement
|
Two
techniques are used to determine infiltration capacity:
I) experiments in drip irrigation; ii) rain simulation.
Drip
irrigation experiments
should be applied to an unbroken layer of surface
crust, since the presence of cracks has a strong bearing
on the infiltration capacity of the crust, whereas
it should exclusively be due to gravitational flow.
To exclude the influence of texture on absorption
and to prevent lateral flow of water, the soil surface
should be wet beforehand. Vegetation has to be eliminated
to prevent it intercepting water. Water is poured
from a container with a constant level equipped with
a drip. The flow rate Q, also constant, is measured
according to a millimetric scale applied to the container
and a watch. On the ground around the drip, a damp,
generally oval shaped patch is formed which becomes
increasingly large until it stops expanding after
about thirty minutes. The contours of the patch are
marked with pegs after which the experiment is repeated
at least twice with decreasing flow rates at each
time; the damp patches, which have become smaller
and smaller, are also pegged out. Thus three damp
surfaces are created and their diameter and then their
respective surface areas are measured (A). After this,
the infiltration rate qi is calculated by means of
the Darcy equation. The flow rate is calculated by
Q=A*qi.
The
rain simulation experiment can be carried out
with the help of simple portable rain simulators.
It is important to identify a number of sites sufficiently
representative of the source area and for each site
at least four different simulations of differing intensity
should be carried out in comparable plots. Rain intensity
is calculated on the basis of variations in the level
of water in the instrument's tank during a certain
time interval.
|
|
Limits
of the indicator
|
These
are mainly limits of an operational nature due to:
the high cost, both in terms of time and of personnel,
of surveys; the difficulty of identifying a number
of sufficiently representative sites within the same
area; and the difficulty of finding comparable plots
within the same site, i.e. with characteristics that
are not likely to bias the subsequent statistical
data analysis.
|
|
Linkages with other
indicators
|
Infiltration capacity,
along with Soil surface stability, is part of
a system designed to identify and characterise in detail,
then to classify, a series of source areas, (areas that after
the advent of rainfall of varying intensity become sources
of sediment and surface flow).
|
5.
Evaluation of data needs and availability
|
Data required to calculate the indicator
|
Data must necessarily be obtained from
specific field surveys.
|
|
Data
sources
|
|
|
Availability
of data from national and international sources
|
|
6.
Institutions that have participated in developing the indicator
|
Main
institutions responsible
|
University
of Amsterdam, University of Lisbon.
|
|
Other
contributing organizations
|
|
7.
Additional information
|
Bibliography
|
Imeson
A.C., Suryana N., Bergkamp G., Bolwidt L., Haring
R., van Leuzen P., Seijmonsbergen H., Hoogteiling
D., (1999). Developing and applying indicators of
desertification derived from soil-water-vegetation
relationships. Mediterranean Desertification and Land
Use - Final report phase III (1996-1999). Contract
ENV4-CT95-0119. Thatcham, UK, pp. 47-85.
|
|
Other
references
|
|
|
Contacts
Name and address
|
Dept.
Physical Geography and Soil Science
University of Amsterdam, The Netherlands.
Tel: (31) 20 525 7457
Fax: (31) 20 525 7431
Email: A.C.Imeson@frw.uva.nl
|
|
