ῐ
J. Jpn. Soc. Soil Phys.
῏῍ῌῐῑ῎
No. 23, p. -/ῌ., ῍,**,῎E#ect of Groundwater Level on Salinity Content
and Environmental Land Classiﬁcation
Chaiyanam DISSATAPORN*, Kane YACOUBA**, Machito MIHARA**
and Rokuro YASUTOMI*** Land Development Department, Thailand** Faculty of Regional Environment Science, Tokyo University of Agriculture
Abstract
Saline a#ected soil is in the northeast of Thailand, especially in the Khon Kaen Province. The
relation between the salinity accumulation in brackish groundwater and the groundwater levelfrom ground surface represents the progress state of soil salinization.
The practice for suitable land use against the salinization can be established when the main
conditions of salinization hazards are known. Based on this concept, the electric conductivity (EC)of groundwater and its level were measured with piezometers for three years in an experimentalﬁeld at Khon Kaen Province. The ﬁeld data showed that the groundwater level much a#ected bysalinity was less than one and half meters from ground surface in the investigated area, and it was
conﬁrmed that the saline soil was mainly caused by the capillary rise of brackish water and by theaccumulation of salt occurred at the soil surface.
Salt accumulation process was investigated by the change in groundwater level. The reducing
e#ect of salinization caused by capillary water rise became remarkable when the groundwaterlevel was lowered until ground surface soil was out of the dominant capillary water zone.
This indicates the reduction of groundwater level was very e#ective in reducing salinization.
Allowing for ﬁeld experimental results, a classiﬁcation map for environmental land use in saline
a#ected area was proposed.
Key words : salinization, capillary water, salt movement, land reclamation, land classiﬁcation+.

Introduction

The prevention of soil salinization is one of
the methods for environmental protection
against deterioration of water and land resources. Many of the agricultural lands in the
Khon Kaen Province, northeastern Thailand,
were cultivated from woodland and forest.
Some low-lying land gave rise to saline soils,
which occurred after the clearing of forest.
Sodic soils were also produced through capillary water rise induced by the high rate ofevapotranspiration, sometimes through ﬂoods.
A number of regions, arid and semi-arid, suchas the northeast of Thailand as well as Mauri-tania in West Africa and others are still being
a%icted with salinization problems and thedeterioration of land productivity.
To decrease the rate of salinization, leachingof the accumulated salts by ﬂooding or drip
irrigation have been found to be e#ective(Goldberg and Uzrad, +310). Farming systems
such as multi cropping or agroforestry are also
said to be e#ective. This idea is based on thefact that mixing fruit plants with cover crops
take up soil moisture e$ciently. The surface
soil moisture content is taken up by shallow
rooted plant such as grass, while the deeper
subsoil moisture is tapped by deep roots,
guaranteeing an e#ective moisture up-take.

῏  23

36

Thus, a reduction in salt accumulation will bepossible (Lovenstein et al., +323). This plantcultivation technique for soil salinity prevention is still empirical. Interruptions of rainfall
and the capillary water rise to the soil surface
using trees are one of the measures for preventing salinization hazards (Dissataporn et al.,,**+ a).
The ﬂuctuation of groundwater level varied
from season to season, and the annual change
in the level was large in the area. Accordingly,
it is not practical to set up a large scale (morethan +** ha for an example) land development
project in the saline area. A small scale project(several ha) is rather suitable for each farmer
because the degree of salinization changes byplaces so that multi cropping land use, andprivate land improvement will be beneﬁcial.
The hillside is usually used for orchard, eucalyptus and cassava cultivation, and the low
land for paddy ﬁelds. For making an environmental land classiﬁcation map for rehabilitation, ﬁeld observations of the ﬂuctuationof groundwater level and its salinity were conducted in this study.
,.

,**,

Fig. +

Topography of investigated ﬁeld with
contour lines above mean sea level andlocation of piezometers (P).

Fig. ,

Soil proﬁles in piezometer P+, P+, and P+-.

Materials and Methods

The ﬁeld experimental site, located ,/ km
southwest of Khon Kaen in the northeast of
Thailand, has an altitude ranging from +11 to+2. m above mean sea level. An annual rainfallof 3-/ mm and soil salinization are strikingly
damaging the area, especially in low land
which gets water logged during the rainyseason. However, the dry season brings abouthigh evaporation rates amounting to ,,*,* mmin a year. The surface soil texture in the area isclassiﬁed as sandy loam (SL) to loamy sand(LS) which belongs to a kind of the lateritic
soils (Wada, +332).
The low land area was much a#ected bysalinization, and ECe (electrical conductivity ofsaturate soil extract) of surface soil was generally over ,* dS/m. Values of more than -* dS/m appeared during the dry season in low land
where salt accumulation had badly damaged

the soil. In the hillside area, the ECe of thesurface soil on average was generally less than+* dS/m through the year.
The items of ﬁeld experiment consisted ofmonitoring of groundwater level ﬂuctuation inall seasons and of estimating the relationshipbetween groundwater level and salinization.
The groundwater level was deﬁned here as the
distance from ground surface to groundwaterlevel. Thirty seven spots were selected in thisstudy area included an area of *.1 km*.1 km
in view of the topography (Fig. +). Piezometers῏῎ : E#ect of Groundwater Level on Salinity Content and Environmental Land Classiﬁcation

Table +

37

Annual standard deviation of groundwater level and electric conductivity of groundwater
Year

+330

+331

+332

Standard deviation of groundwater level from ground surface (m)Standard deviation of electric conductivity of groundwater (dS/m)*41+.43.*

*4.0+
-40*/

*4,1+
,42.,

Table ,

Changes in groundwater level between rainy and dry season (Khon Kaen +330)

Maximum di#erence (m)Average di#erence (m)Low landIntermediate land

Hillside

,40*
*4.0

,4,/
*421

,4.0
-4+1

(P+ to P-1) were set up at each spot to monitor
the groundwater level and its salinity (EC).
Several piezometers did not work properly
after setting owing to breaking down or ﬂoods
so that actual measuring points were ,/ to ,1 in
number, depending on the year. All the depthof piezometers installed was 1 m.
The area investigated was practically divided into three areas based on the contour lines.
These are hillside (῍+2* m high from mean sea
level), low land (ῌ+12 m) and intermediate land
between +12 m and +2* m. The data from eachpiezometer were collected monthly for three
years from +330 to +332. The salinity of thesurface soil (ECe) was measured at several
points. The typical soil proﬁle P+ for the lowland, P+, for the intermediate land and P+- forthe hillside were shown in Fig. ,. The proﬁle ofthe hillside (P+-) is stratiﬁed by SL, while thatof the low land (P+) has ﬁner particles layers
like clay loam (CL) at the depth of *.2 m whichis rather impervious than LS. From these textures, the soil types of the area were classiﬁed
as SL in the surface soil.
-.

Results and Discussion

EC change of groundwater on annualbasis
The groundwater level during +331 and +332
was lower compared with that in +330, which
increased the intensive evapotranspiration
rate during the dry seasons. Standard deviations of the level showed that +330 was the year-. +of ﬂood and high level of groundwater (Table+). From the data, it can be seen that mostﬂuctuations in groundwater level and EC
values occurred in +330.
During +330, the di#erences between the
maximum and minimum groundwater level ofpiezometers indicated less than ,.0* m in low
land and ,..0 m in the hillside (Table ,). The
average groundwater level changes of the piezometers between the rainy and dry seasons
were *..0 m in the low land and -.+1 m in thehillside.
The EC values of groundwater were taken as
mean values of the ﬂuctuating groundwaterlevel for each three consecutive years (Fig. -).
The remarkable di#erences in the averagegroundwater level between the rainy and dry
seasons were observed at the hillside. The low
land and even hillside were often in ﬂood after
a heavy rainfall. The EC values of groundwater doubled from +330 to +331, especially inthe area where the groundwater level was lessthan , m (Fig. .). The increase in salinity ofgroundwater was more conspicuous in the low
land, while the groundwater deeper than , m
had no remarkable increase in salinity. There
was almost no general change in +332 compared to the previous year.
It was supposed that the soil surface wasenough covered in the reach of capillary risewhen the groundwater level was shallower
than + m from ground surface. In this case, thesoil surface was heavily damaged by the salt

38

Fig. -

Fig. .

  23,**,

Fig. /

Example of ﬂuctuation of groundwaterlevel from ground surface in period
during +330 to +332 in P+ piezometer.

Fig. 0

Example of ﬂuctuation of electric
conductivity of groundwater in period
during +330 to +332 in P+ piezometer.

Electric conductivity of groundwatertaken from piezometers for three years
observation (+330ῌ+332).

Electric conductivity of groundwater
against groundwater level from groundsurface.

accumulation. In these circumstances, if thecapillary rise was controlled or reduced, thesalinization hazards could be minimized using
plants, and a new soil improvement practicewill be established (Dissataporn et al., ,**+ b).
-. , Measurement of soil salinity andgroundwater level
It is assumed that the soil salinization process is a function of groundwater level, watersalinity of groundwater and evapotranspiration. The data of site P+ is shown as an example in Fig. / and Fig. 0. The salinity of surface
soil was remarkably a#ected by going up ofgroundwater level. In Figs. /, 0 for an example
of P+, when ﬂoods covered the surface, EC
values of surface soil increased sharply. There
were many ﬂoods in the low land, a discharge
area of groundwater where the salinity waseasily condensed, while the hillside is a re-charge area of groundwater by percolation
through the soil.
The salinity of surface soil was increasing
when the groundwater was shallow. As an
example shown in Fig. 1, the ECe values of
surface soil (*ῌ,* cm in soil depth) were between ,* dS/m and ,2 dS/m.
When thegroundwater level was lower than + m from thesurface during the dry season in +331, ECe ofsoil in P+ was lower than ,* dS/m. The soil,
during the rainy season in +330 and dry season
in +330, had higher salinization than thatduring the dry season in +331, because groundwater levels during the rainy season in +330
and dry season in +330 were *.*0 m deep and*.0- m deep from the surface, respectively. This
indicates that the groundwater deeper than + m
did not give much impact on salinization of thesurface (Fig. 2).
Using the estimate equation of capillary riseH1//d, where capillary height H mm andaverage particle diameter d mm, and another῍ῌ : E#ect of Groundwater Level on Salinity Content and Environmental Land Classiﬁcation

Fig. 1

Changes in electric conductivity ofsaturated soil extract with soil depth inP+ piezomter.

Fig. 2

Relation between groundwater leveland electric conductivity of soil in P+
piezometer.

experimental equations (Scott, +30-, Tabuchi,+31+), the capillary rise was calculated in between 3* cm and ++* cm for the soil proﬁlesgiven in Fig. ,. As the capillary height calculated for P+ fell within 32 cm to +** cm, a critical value for capillary rise may be at about + m
deep from ground surface (Yacouba, ,**+).
Groundwater makes it possible that capillarywater from shallow groundwater level is easily
connected to the surface soil. When the severe
evaporation of the water at soil surface urges
the movement of capillary water, the salt accumulation of water soluble salt contained incapillary water occurs in the low land.
Based on the data obtained in Iran(Matsumoto, +33/), the concentration ofsalinized soil was extremely high at a groundwater level of about 1* cm from ground surface, but if the groundwater level was as deep

39

as , m, the salinization was outstandingly restricted in the case of salt a#ected area.
According to the report by Watanabe et al.
(+332), the upward movement of water consistsof two types, one is liquid water movement by
capillary, the other is by vapor which did notconvey the salinity. From these experimental
investigations, it could be guessed that the lesssaline a#ected soil depends mainly on the typeof vapor movement, and much saline a#ectedsoil on that of the liquid water movement.
Therefore the reducing e#ect of salinization
by capillary water will be remarkable when the
groundwater level is lowered until the surface
soil is out of the dominant capillary water zone.
From above discussion, it can be proposedthat much a#ected area of salt is classiﬁed asvulnerable area A where the top capillary rise(H) situates above ground surface, and lessa#ected area as safer area B where the top of
capillary rise situates below ground surface,respectively.
-. - Salinity based soil classiﬁcation forland use
It can be possibly taken for granted thatsalinization proceeds in the case of the experimental ﬁeld when the capillary water range issituated between * and +./ m, rain water caneasily leaches down the accumulated salts tocondense the groundwater salinity.
The
percolating front of rainwater will induce thecapillary front to go up when they are connected. Then groundwater comes up again to thesurface during the seasons. On the other hand
there is no rapid increase in the soil salinity inthe range deeper than , m where capillarywater rise does not arrive quickly at the
ground surface, though the salinization may
proceed gradually for a long time if no rain.
Reducing the capillary water movement isdecisively important for the prevention of soil
salinization. The up and down movement in allseasons will condense the groundwater salinity
in the ﬁeld. This type of ﬂow will also get thesurface salinization to increase.
On the basis of Fig. ., it became clear that the40ΐῐ῎῔῕ῑ ῒ 23 ῏ ῌ,**,῍

critical level between the area A (much a#ected capillary zone) and the area B (less a#ectedcapillary zone) in the ﬁeld site may be situatedbetween +./ m and , m. The level more than ,m shows that the water quality of groundwater will be useful, if the quality limit of EC
for irrigation is - dS/m (Ayer and Westcot,+310) because over which the relative land productivity decreases remarkably though it
depends on a variety of crops. When the soil
salinization increases up to +* dS/m in ECe, theyield may be drastically damaged (Carter,+32+). The quality of groundwater EC observedin the ﬁeld was about / dS/m, so that it will be
useful for irrigation if it is diluted by fresh
water.
Accordingly, it may be useful for minimizing
the salt accumulation to provide a map showing as follows. The area A is vulnerable to becontaminated by brackish water (less than +./m level from ground surface), the area B is noteasily contaminated by the water (deeper than
, m from ground surface) if well managed, andthe area C is in between both areas. Based onthese standards, the areas with salinization
problem can be classiﬁed as shown in the map(Fig. 3).
The map may o#er a useful data for landdevelopment as well as land conservation andrehabilitation planning in the region with salt
problems. For the area A, reducing groundwater level will be e#ective to reduce the salinity. The irrigation water for leaching will beobtainable from the groundwater in the area B.
The agroforestry cultivation system toreduce the evapotranspiration and to reducegroundwater level will be expected applying
high water use and fast growing trees as
Eucaliptus to the recharge area of groundwater, in particular reforestation may be e#ective in the area B, because the area A and B are
linked with groundwater. If a quick and inexpensive method to identify the salinity in the
ground is applied, the map will be delineatedeasily (Dissataporn et al., +330).

Fig. 3

Land classiﬁcation map of soil a#ectedby salinity using annual averagegroundwater level from ground surface(counter lines fo groundwater level).

..

Conclusion

Capillary rise of groundwater was one of themain causes of salinization. Therefore themost important practice for salinization prevention is to interrupt capillary water rise, andto reduce the groundwater level. In the case of
the site investigated, salinization proceeded
quickly in the area where the annual averageof groundwater level was shallower than +./ mfrom ground surface.
When the surface is out of the much a#ectedzone by capillary rise, the application possibility of plant root system and agroforestry toabsorb the salinity will be worth considering.
A practical way of improving the soil in thearea A is to lower the groundwater level bydrainage to the depth of more than +./ m fromground surface. The leaching with ﬂood irrigation using the groundwater from the area B῍ῌ : E#ect of Groundwater Level on Salinity Content and Environmental Land Classiﬁcation

and C to area A will be useful. The applicationof an agroforestry system in the area B and thearea C may be useful as a practice of the soil
improvement by reducing water supply to thearea A.
Acknowledgements
I would like to thank Prof. Dr. ANASE, M. for
his advices during the course of this work.
Thanks are also due to Mr. Yamclee, P. and his
sta# of Soil Salinity Research Section, Land
Development Department for their assistancein carring out the observation in this study.
References
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41

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