|
1. Definition
| Name |
DRAINAGE |
| Brief
definition |
Drainage refers to how
rapidly excess water leaves the soil by runoff or internal
drainage. Drainage can be used to describe the downward but
also the upward movement of water in the soil profile.
 |
A
poorly drained soil with a permanent ground water table
in about 0.8 meter from the soil surface (photo by C.
Kosmas) |
|
| Unit of measure |
None |
2. Position
within the logical framework DPSIR
3. Target and
political pertinence
| Objective |
Contribution
to the definition and mapping of ESAs, definition of desertification
risk of lowlands. |
| Importance
with respect to desertification |
Soil erosion
and salinization are two of the most important processes of
land desertification. Soil erosion affects mainly hilly areas,
while salinization affects mainly lowlands. Salinization is
related to the depth of groundwater (drainage), quality of groundwater,
soil texture, rainfall, evapotranspiration rate etc. Lowland
areas along the coastline with poorly drained soils developed
on alluvial Quaternary deposits are very vulnerable to salinization
and desertification under arid or semi-arid climatic conditions.
It is estimated that about 15% of the lowlands in the Mediterranean
region are highly affected by salts or are vulnerable to salinization.
|
| International
Conventions and agreements |
The CCD emphasizes
that combating desertification must be tackled within the general
framework of actions to promote sustainable development. |
| Secondary objectives
of the indicator |
Within the
ESA model: a) investigation of the individual processes linked
to land degradation and desertification, b) processes linked
to salinization. |
4. Methodological
description and basic definitions
| Definitions
and basic concepts |
When rain or irrigation
ceases and no more water is ponded, infiltration of water
from the soil surface comes to an end. Downward movement of
water within the soil continues as soil water redistributed
within the profile. The downward movement of water is called
internal drainage and its effects are to redistribute soil
water to lower depths of the profile, thereby increasing the
water content at the subsoil.
Drainage is classified
in classes according to the term which generally describes
the condition of how long the soil is free of saturation as
following: (a) excessively drained soils in which water is
removed very rapidly and no occurrence of internal free water
is observed, (b) well drained soils in which water is removed
from the soil somewhat slowly during some periods of the year
and soils can be wet for a sort time within the rooting depth
during the growing period, (c) moderately well to somewhat
poorly drained soils with Fe, Mn or grey mottles present in
the soil, at some depth between 30 and 100 cm from the soil
surface, the soil is wet enough near the soil surface or the
soil remain wet during the early growing period of the plants,
and water is removed from the soil slowly, (d) poorly to very
poorly drained soils with mottles of Fe and Mn present in
the upper 30 cm of the soil, or grey colours of reducing conditions,
with a permanent water table usually at a depth greater than
75 cm. In some of these soils the ground water may reach to
the surface during the wet period of the year. Water is removed
from the soil so slowly that these soils are wet at shallow
depth for long periods.
|
| Benchmarks
Indication of the values/ranges of value |
- well drained
- imperfectly drained
- poorly drained
|
| Methods of
measurement |
Field method
through the observation of occurrence of hydromorphic features
such as iron or manganese mottles or concretions of iron and
manganese or grey colours in a soil profile 1.5 meters deep.
|
| Limits of the
indicator |
Drainage is
especially important for plain areas in which shallow ground
water table exists with high concentration of soluble salts.
Drainage is not so important for hilly sloping areas. |
| Linkages
with other indicators |
Soil
texture, Soil depth, Slope
gradient, Land use type,
Vegetation cover, Rainfall,
Aridity index (1). |
5. Evaluation
of data needs and availability
| Data required
to calculate the indicator |
Presence of
hydromorphic features (iron and manganese mottles or concretions
or grey colours) in the soil profile (depth 1.5 m or less if
presence of bedrock). |
| Data sources |
Necessary data
are usually available and accessible from regular survey reports
and the cost/benefit ratio is reasonable. |
| Availability
of data from national and international sources |
Data
can be obtained from various regional, national or international
institutions involved in collecting and elaborating soil survey
data.
|
6. Institutions
that have participated in developing the indicator
| Main institutions
responsible |
Agricultural
University of Athens
|
| Other
contributing organizations |
Universities
of Lisbon, Murcia, Basilicata, Amsterdam, Leeds
|
7. Additional
information
| Bibliography
|
Kosmas, C.,
Kirkby, M. and Geeson, N. 1999. Manual on: Key indicators of
desertification and mapping environmentally sensitive areas
to desertification. European Commission, Energy, Environment
and Sustainable Development, EUR 18882, 87 p. |
| Other references |
Rounsevell,
M., and Loveland, P., 1994. Soil responses to climate change.
NATO ASI series I: Global environmental Change, Vol. 23, 312
p. |
| Contacts
Name and address |
Agricultural University
of Athens, Laboratory of Soils and Agricultural Chemistry,
Iera Odos 75, Athens 11855, Greece
Dr Constantinos Kosmas
email: lsos2kok@aua.gr
|
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