1133
A Geotechnical Countermeasure for Combating Desertification
Une mesure géotechnique pour lutter contre la désertification
Liu Q., Yasufuku N.
Department of Civil Engineering, Faculty of Engineering, Kyushu University, JAPAN.
ABSTRACT: A self-watering system and the design method are proposed. The self-watering system, which can collect and store all
kinds of water, comprised of the simple ground is much efficient to support surface vegetation. The system is designed by installing
soil structures into original sandy ground. Finer soils or artificial materials can be used as the materials of the soil structures. The
system can continually raise the ground water to a certain depth in the sandy ground using the capillary force. Moreover, it can
minimize the evaporation from the system, which provides the potential to prevent salinization. To design the system practically,
information like soil water retention curve, hydraulic conductivity and other information such as planting density and weather
condition are needed. The self-watering system works under the condition of no extra energy input.
RÉSUMÉ : Un système d'auto-arrosage et le procédé de conception sont proposés. Le système est conçu en installant des couches de
sol fin dans un sol sableux d'origine. Les sols fins ou es matériaux artificiels peuvent être utilisés comme les matériaux de la structure
du sol. Le système peut élever continuellement l'eau du sol à une certaine profondeur dans le sable à l'aide de la force capillaire. En
outre, il peut minimiser l'évaporation du système, ce qui offre la possibilité de prévenir la salinisation. Pour concevoir ce système en
pratique, des informations comme la courbe de rétention d'eau du sol, la conductivité hydraulique et d'autres informations telles que la
densité de plantation et les conditions météorologiques sont nécessaires. Le système d'arrosage fonctionne dans la condition de non
apport d'énergie supplémentaire.
KEYWORDS: unsaturated soil, desertification.
1 INTRODUCTION
Desertification is the degradation of land in arid, semi-arid, and
dry sub-humid areas due to various factors: including climatic
variations and human activities (UNCCD 1994). The rapid
expansion of desertification has resulted in serious
environmental
deterioration,
economic
loss,
locally
unsteadiness political situation and social upheaval. Because of
the serious situation of desertification, prevention of the
degradation of land becomes key issue. Among existed
countermeasures, greening is considered to be one of the most
effective methodology which can protect the biodiversity
threaten by desertification, minimizing cost and providing
positive multifunction. In the application of the methodology,
the vegetation is the core. However, in order to fulfill the
requirement of the growth of the plants, available water
resource is the one of the important limitation. In arid land,
groundwater is usually used as one of important water
resources. Therefore, the technical methodology is suggested,
which use groundwater to fulfill the requirement of the growth
of the plants. However, there are numerous barriers to its
implementation. One of these is that the costs of adopting
sustainable agricultural practices sometimes exceed the benefits
for individual farmers, even while they are socially and
environmentally beneficial. Another issue is the simplicity of
the technique to be acceptable by local people. From the
geotechnical and geoenvironmental point of view, any
technique should solve the issues such as, mechanism of raise of
the groundwater up to the root zone of the plants, prevention of
the salinization of the ground and design of the system that can
sustainably provide the water to the plants.
In arid or semiarid area, which characterized by lack of
available water, water is one of the main limitations to the
growth of plant. Frequently, capillary fringe is too deep to be
used by plant in these areas. The self-watering system has been
proposed. The self-watering system, which is designed to
collect and store all kinds of water, comprised of the simple
ground is much efficient to support surface vegetation. A self-
watering system and the design method are proposed. The
system is designed by installing soil structures into original
sandy ground. Finer soils or artificial materials can be used as
the materials of the soil structures. The system can continually
raise the ground water to a certain depth in the sandy ground
using the capillary force. Moreover, it can minimize the
evaporation from the system, which provides the potential to
prevent salinization. To design the system practically,
information like soil water retention curve, hydraulic
conductivity and other information such as planting density and
weather condition are needed. The self-watering system works
under the condition of no extra energy input.
2 SELF-WATERING SYSTEM
The soil layer often provides a medium to plant for its
requirement of rooting, water and nutrient. The water flow has
effect on physical property, such as consistence, strength of
aggregates, aeration and temperature of soil, which is relevant
to the growth condition of plant. The most direct effect of the
water condition of soil is that it influences the growth of plant.
The root of plant can absorb the amount of water to fulfill its
need for transpiration and the amount of solute for its mineral
nutrient. The transpiration water disappears in atmosphere as
vapor condition. Finally, a water flow moves through soil
towards to root.
In arid or semiarid area, which is characterized by lack of
available water, water is the main limitation to the growth of
plant. Frequently, capillary fringe is too deep to be used by
plant in these areas. The self-watering system, which is
designed to collect and store all kinds of water, comprised of the
simple ground is much efficient to support surface vegetation.
The design target of this system is to setup an equivalent
condition between the storage capacity of water and rate of
usage.
The maximum water content can be held in soil before it
drains downwards is field capacity,
θ
fc
, which is water content
when drainage ceases. Field capacity is closely correlated to the
volumetric water content retained in soil at -33 kPa of suction
(Richards and Weaver, 1944). The capillarity storage capacity
(CSC) in unit area of a soil layer can be determined by
integrating its volumetric water content over its thickness,
m
, it
can be described by
