The Effect of Rainfall Intensity on Soil Erosion and Runoff for Latosol Soil in Indonesia

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Bul. Agron.(31)(2) 71- 79(2003)

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The Effect of Rainfall Intensity on Soil Erosion and Runoff
for Latosol Soil in Indonesia
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Sukandi Sukartaatmadjal), Yohei Satol), Eiji Yamajf), Masaya Ishikawa3)

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ABSTRACT

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Soil erosion is the most seriousproblem of land degradation in Indonesia.However, limited report has been
documented.The erosionproblem in Indonesia,particularly in Java, has beenat an alarming rate. Thefundamental
caseof soil erosion is the rain effect upon the soi/. Rainfall intensityand soil characteristicsare related to soil erosion
and runoff The objective of this researchwas to study the relationship of rainfall intensity,soil erosion and runoff in
latosol soi/. An experimentwas conductedusingplot size 22 m in length and 2 m in width and 9 % slope. A field
experimentwas conductedwith rainfall intensityobservationfor 3 months,to collect soil erosionand runoff in the soil
collector. A laboratory experimentwas doneusing rainfall simulator instrumentswith rainfall intensityof 2.3, 3.4, 4.5,
5.6 cm/hr and 8 % slope each with 3 replications. Theresult of the experimentsshowedthat soil erosion was 3.14 t/ha
and runoff was 33.20 m3/ha.Whenthe rainfall sizeincreasedthe soil erosionand runoff also increased.Thecorrelation
coefficientbetween£130 (Interaction130and energy)and soil erosionwaspositive.
Key Words:Rainfall intensity,Soil erosion,Latosolsoil
"
INTRODUCTION
Soil erosion is the removal of soil from land
surfaceby running water (Schwabet a/., 1981). It is a
processof soil detachmentand transportationfrom soil
agent of erosion (Arsjad, 1989). While it is generally
acknowledgedthat erosion is serious in Indonesia,no
analyticalor systematicstudieshavebeenundertakento
documentwatershed;records of 6.0 mm/year and 1.7

ml?/year were calculated from sedimentconcentration
(Smukaban,1989).
Under intensetropical condition with largeamount
of rainfall, severe soil erosion results (Barus and
Suwardjo, 1977). The situation is aggravatedby the
rough terrain and steeptopographyin the mountainous
area of Java, Sumatera,Sulawesi, The Lesser Sunda
Island and Irian (Sinukaban, 1989). Thus erosion
damage resulting from floods occurs widespread in
Indonesia(Bams and Suwardjo,1977).
Rainfall is high during wet season,which resultsin
increaseof soil erosion (Hardjowigeno, 1989). Large
areaof latosol is found in CisadaneWatershed.Most of
land is used for agriculture. Total critical land in
CisadaneWatershedis 14733ha and mostly situatedin
Bogor District (Sukartaatmadja,1992). Intenserainfall

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in erosivesoil, steepslopesand poor land management
in Indonesiacan causeserious soil erosion and water
pollution (Arsjad, 1989).
Latosol soil in Indonesia is important for
agriculture, but soil erosion especially in land with
slopes, and high rainfall intensity tends to be high.
Therefore, it need protection from soil damage
(Sukartaatmadja,1992). Researchon rainfall intensity,
soil erosion and runoff is neededfor protection of soil
from erosiondamage(FAO, 1965).
The purpose of this researchwas to study the

effect of rainfall intensity on soil erosionof latosol.The
most importantcharacteristicof soil in relation with soil
erosionwas erodibility. The researchwas to determine
the valueof soil erodibility.
MATERIALS AND METHODS
Plot size of 22 m x 2 m and land with 9 % slope
was usedfor field experiment.The field experimenthad
a soil collector for measuringsoil erosion and runoff
after eachprecipitation.The experimentwas conducted
at the experiment station, Bogor Agricultural

I) Senior Lecturer, Bogor Agricultural University, Indonesia
2)Professor, The University of Tokyo, Japan
3)Assistant Professor, The University of Tokyo, Japan

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Bul. Agron. (31) (2) 71- 79 (2003)

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University, Darmaga,Bogor, Indonesia.Observationof
rainfall in the location was donein 3 months.
A laboratory experiment was done to identify
relationship between rainfall and soil erosion, and
control for experiment in the field. The result of
laboratory experiment was used to estimate field
experiment,Rainfall simulator instrumentwith rainfall
intensity 2.3, 3,4, 4.5 and 5,6 cm/hr and land slopeof 8
% was used. Soil sampleswere taken from latosol soil
at Darmaga,Bogor,
Soil ~amplebox 30 cm in width, 59:5 cm in length
and 5 cm In depthwas then prepared,Soil collector was
usedfor measurementof soil erosion and runoff. Time
of experimentfor each replicate was one hour. Before
treatment of soil sample it was set in field capacity
condition, Soil infiltration in the box of soil sample
neededtime and runoff was collected in the soil and
water
collector.

erosion in. ~the
I of soil
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d Experiment
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a oratory use raInla slmu ator wit I erent raInla
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Intensity,The soil erosionwas collected
In soilthcollector
Th
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. hed In
. wet condItlon.
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and welg
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In oven, 01 partlCes use was e ow mm, 01 u
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d' ,
fi
fi Id
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enslty was same con Itlon as or Ie experIment
(0.899g/cm3).

Rainfall erosivity was calculatedusing formula E
= 13.32+ 9.78 log I and EI = E x 130,and Re = EI x 10.

2 where E= Kinetic energyof rainfall (Joule/m2/mm),I
= Total Rainfall (mm) , EI = Index of potential erosion,
130= Rainfall intensity maximum 30 minutes (cm/hr),
Re = Rainfall erosivity. Soil erodibility was calculated
using formula K = AIR x LS x CP where K = Soil
erodibility, A = soil loss (ton/ha/year),R = Erosivity
factor, K = Erodibility factor, LS = Slopesfactor and
LS= Land management factor. The rainfall was
mea~uredat D~a~a station wi~ latitude of 60 ┬░30! S,
longitudeof 106 45 E, and elevationof 250 m.

RESULTS AND DISCUSION
Precipitationand Erosivity
M
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ean 0 preclpl Ion at Darmagawas 294. I mm
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th Th h' h t
thl

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per mon.
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ovem er, w lee
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In July. Monthly precipItationat Darmagastation firom
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Figure 1, Monthly precipitation from 1964 to 1998 at Darmaga Station

72

SukandiSukartaatmadja,
Yohei Sato,Eiji Yamaji, MasayaIshikawa

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Bul. Agron. (31) (2) 71 - 79 (2003)

Table4. Soil physic and organicmatterfrom field experiment.
Soil physic and soil organicmatter

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Mean

Bulk density(depthof soil 0-15 cm) (g/cm3)

0.899

Texture (%)

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Clay

70.715

Loam
Sand

23.740
5.545

OrganicMatter (%)
C
N
C/N

1.860
0.195
9.500

Soil bulk density of field experiment0.899 g/cm3
indicatedcomparisonbetweensoil dry weightswith soil
volume. An increase of soil bulk density caused
condition of soil compaction and related with
infiltration and root growth. The value of soil bulk
densitylower than 1 causedeasywater to flow through
the soil (Hardjowigeno,1989).
Soil texture of field experiment was clay loam.
With 40% - 60% clay, the soil was very sensitiveto soil
. . mineral
erosion.The stability of. soil dependson clay
(Morgan,
1979).., The soIl was not good 0"as IndIcated by
.
organIc

matter

m the soIl

lower

than

10 Yo. SoIl

increasedcapacity of cation exchange.(Hardjowigeno,
1989).
The resultof measurement
on soil infiltration was:
1c= 1.241to,17
Ir = 12.65t-183
WhereIc = Infiltration accumulation( cm)
Ic = Rateof infiltration ( cm/hr)
1
T = time(minute)
;
Runoffand Soil erosion
Runoff and SOl
.1 erosIon
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were measure
d after
.
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erosIon

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an runo cou
ecreaseSOl organIc ma er
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and Turk, 1986). High organic matter and soil clay

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SOl erosIon

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Table5. Runoff and Soil erosionfrom field experimentin 1990.
Date

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Soil erosion
(kg/ha)

Aug 21
Aug 25
Aug 30

0.540
1.077
2.729

Sep

1

4.531

78.204

Sep

7

7.261

565.840

Sep
Sep
Sep
Sep
Oct
.,

Runoff
(m3/ha)

10
14
22
23
13

0.250
0.472
29.613

9.106
0.756
11.111
0.970
16.489

226.659
0.863
1594.045
53.522
3167.341

Oct 22
Oct 30

55.927
58.927

581.750
5501.364

Oct 31

94.822

8118.273

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TheEffect of Rainfall Intensity on Soil Erosion ..",

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Bul. Agron. (31) (2) 71 - 79 (2003)

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100
90
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RO=0.9531130-29,788
R=0.9341

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60

80

100

120

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140

130

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Figure4. Relationbetween130andrunoff from field experiment

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The lowestrunoff from field experimentis 0.540

'Totalsoil erosionof 3 monthsobservation
was 24.99

m3!haand the highestis 94.792m3!ha. Runoff occurred
after sufficient water infiltration. Runoff influencedsoil
erosion. Relation of rainfall intensity 30 minutes(130)
and runoff is shown in Figure 4. Runoff dependedon
130 because rainfall intensity 30 minutes increased
runoff (Morgan, 1979).
The result of soil erosion from each rainfall was
different. The value ranged from 1.1 g/44 m2 with
rainfall intensity of 29 mm/hr to 36720.4g/44 m2 with
rainfall intensity of 122 m/hr. Rainfall intensity,kinetic
energy and interaction between130 and energy (EI30)

:t/ha. The relation between130 and soil erosion in field
experimentis shownin Figure 5.
The rainfall from August to October was normal
but was not the maximum in the wet season. Soil
erosionwas higher in the wet season.If it is higher than
12.3 t/ha/year,it will have detrimentalto land resources
(FAO, 1965).Observationof soil erodibility in the field
experimentwith soil erosionand rainfall erosivity gave
a value of 0.017. This factor indicatedthat soil in the
field experiment was not very sensitive with soil
erosion. Clay soil texture from field experiment with

were parameters
that haverelationwith soil erosion.

sloperelatedto theincrease
of soilerosion.

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30

40

50
130

60

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80

90

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Figure 5. Relation between 130 and soil erosion from field experiment

76

SukandiSukartaatmadja,
Yohei Sato,Eiji Yamaji, MasayaIshikawa

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Bul. Agron. (31) (2) 71 - 79 (2003)

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Table6. Runoff from rainfall simulator(m3/ha).

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Rainfall
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intensIty
(cm/hr)

L and sIope
(0;