Bogor, 21-22 October 2015
288
2.5 Data analysis 2.5.1 Peak flow
Every pair data rainfall-peak flow were analysed by creating a graph illustrating the relationship between forest cover and peak flow. The forest area which were showing the
most minor changes in peak flow represented the almost flat line was the most optimal forested area.
2.5.2 Low flow
Low flow is calculated based ont he dataflow that occurs at the start of the dry season, which has no rain on the previous month. Further testing whether there is a difference between the
low flow rate in the morning with the low flow rate in the afternoon was coducted using mean different test analysis Independent Sample TTest. Calculations were performed using
SPSS11 module.
2.5.3 Water quality
Each sample consists of 1500 ml water then was analyzed in Laboratory of Indonesia Ministry of Health’s Laboratory, Yogyakarta. Parameters analyzed includes: water colour, turbidity,
TDS, COD, BOD, Fluorine, Sulphate, Chlorine, Nitrite and Nitrate.
3. RESULT AND DISCUSSION 3.1.1
Landcover type
Based on image classification on the study area, it was found four land use types as presented in Table 1.
Table 1: Land cover types of each sub watershed
Sub watershed
Area km
2
Forest Shrubs
Paddy fields
Settlements
Modang 3.38
94.3 2.3
0.19 3.21
Cemoro 13.47
91.1 6.6
0.2 2.1
Kejalen 20.14
80.9 7.9
1.3 9.9
Sambong 27.79
74.8 12
3.2 10.0
Kendilan 48.86
23.0 46.67
17.73 12.6
Gagakan 64.80
47.5 30.7
9.9 11.9
Ngroto 69.80
44.9 30.9
14.3 9.9
From Table 1, it can be seen that forested area are in range of 23 to 94. From the measurement using 20 m x 20 m plots in the watershed teak forest, the canopy closure is
about 30 to 70, whereas from 1 m x 1 m plots understory canopy closure are 20 to 100. Total canopy closure 100was found in teak plantation of class age I. . Paddy fields
commonly are dry land used to grow Paddy and other crops types such as Mays and Cassava with intensive tillage using organic and inorganic fertilizers. Settlements consist of houses and
home garden. The forests are located in the upper part of the sub watershed. Paddy fields are occupied in the lower part, and settelement dominated in the middle and lower part. Whereas,
schrubs spread in the upper, middle and lower part of the Sub watershed.
3.1.2 The relationship between forested areas with peak flow
It was were found two rainfall-peak flow event at December 4 and December 5, 2007; January 28 and August 14, 2008; February 28, 2010; and January 29, 2011. The relationship between
forested area and peak flow in those event can be seen in Figure 1 to 6.
Bogor, 21-22 October 2015
289 Figure 1: Relationship between forested area and peak discharge at December 4, 2007
Figure 2: Relationship between forested area and peak discharge at December 5, 2007
Figure 3: Relationship between forested area and peak discharge at January 3, 2008
50 100
150 200
250 300
350 400
20 40
60 80
100 P
ea k
flo w
lt se
c km
2
Forest area of watershed area
20 40
60 80
100 120
20 40
60 80
100 P
ea k
flo w
lt se
c km
2
Forest area of watershed area
5 10
15 20
25 30
35 40
45 50
20 40
60 80
100 P
ea k
flo w
lt se
c km
2
Forest area of watershed area
Bogor, 21-22 October 2015
290 Figure 4: Relationship between forested area and peak discharge at August 14, 2008
Figure 5: Relationship between forested area and peak discharge at February 28, 2010
f Figure 6: Relationship between forested area and peak discharge at January 29, 2011
5 10
15 20
25 30
35
20 40
60 80
100 P
ea k
flo w
lt se
c km
2
Forest area of watershed area
10 20
30 40
50 60
20 40
60 80
100
P e
a k
f lo
w lt
s e
c km
2
Forest area of watershed area
50 100
150 200
250 300
350 400
450 500
20 40
60 80
100
P e
a k
f lo
w Lt
s e
c km
2
Forest area of watershed area
Bogor, 21-22 October 2015
291 The effect of forest cover on flood peaks becomes less important as the size of the
hydrological event increases. There are some reasons that land use become less important for larger discharges are as follows: 1 the wetter the antecedent condition, the smaller is different
in the discharge between the forested and logged cases, at least as a percentage of discharge; 2 higher discharges occurs only when the antecedent conditions are wet; 3 the difference in
response decrease as discharge increase Birkinson, Bethurst, Iroume, Pelacios, 2010. The size of hydrological event increase, the effect of forest covers on the peak discharge
become less important. However, the pattern is complicated by factors such as catchment scale, soil depth, antecedent moisture content and land management. Forests have influenced
on moderate rainfall event Bethurst et al., 2011. Plantation catchment Hopeaodorata 2 years is more responsive to storm with higher total water yield than in forested catchment
Shamsuddin, Yusup, Noguchi, 2014. 3.1.3
The relationship between forested areas with low flow
The relationship between teak forest area and the low flow showed a tendency that the larger the percentage of teak forest area, the greater the flow rate essentially. This is indicated by
equations that have a correlation coefficient ranged from 0.71 to 0.84 Figure 7 to 12. This means that 71 to 85 low flow rate is influenced by the percentage of forest area, while
29 to 15 are influenced by other factors. Nevertheless, Figure 7 to 12 also present the result of the measurement of July 29, 2013 showing the relationship between the area of teak
forests and low flow with a low coefficient of 0.21. This may due to the effect of 73 mm of rainfall in July 2013 Figure 13. This is in line with the recommendations of Zang and Kroll
2007 that the measurement of the flow rate bases hould ideally be avoided as far as possible from the influence of surface runoff.
Figure 7: Relationship between forest area and low flow using data of 17 July 2012
y = -0.0003x
2
+ 0.0592x - 1.5126 R² = 0.8107
-0.2 0.0
0.2 0.4
0.6 0.8
1.0 1.2
1.4 1.6
1.8 2.0
20 40
60 80
100 L
o w
flo w
lt se
c km
2
Forested area of watershed
Bogor, 21-22 October 2015
292 Figure 8: Relationship between forest area and low flow using data of 18 b July 2012
Figure 9: Relationship between forest area and low flow using data of 19 July 2012
Figure 10: Relationship between forest area and low flow using data of 29 July 2013
y = -0.0006x
2
+ 0.0915x - 2.2106 R² = 0.8397
-0.2 0.0
0.2 0.4
0.6 0.8
1.0 1.2
1.4 1.6
20 40
60 80
100 L
o w
flo w
lt se
c km
2
Forested area of watershed
y = -0.0004x
2
+ 0.0699x - 1.747 R² = 0.7836
-0.2 0.0
0.2 0.4
0.6 0.8
1.0 1.2
1.4 1.6
20 40
60 80
100 L
o w
flo w
lt se
c km
2
Forested area of watershed
y = 0,001x
2
- 0,072x + 7,792 R² = 0,211
0.0 2.0
4.0 6.0
8.0 10.0
12.0 14.0
20 40
60 80
100 L
o w
flo w
L t
se c
km2
Forested area of watershed
Bogor, 21-22 October 2015
293 Figure 11: Relationship between forest area and low flow using data of 11 September 2013
Figure 12: Relationship between forest area and low flow using data of 12 September 2013
Figure 13: Monthly presipitation during 2013
y = -0.0013x
2
+ 0.1984x - 5.191 R² = 0.7112
-1.0 -0.5
0.0 0.5
1.0 1.5
2.0 2.5
3.0 3.5
4.0 4.5
20 40
60 80
100 L
o w
flo w
L t
se c
km
2
Forested area of watershed
y = -0.0007x
2
+ 0.1266x - 3.3351 R² = 0.8508
-0.5 0.0
0.5 1.0
1.5 2.0
2.5 3.0
20 40
60 80
100 Lo
w fl
o w
L t
se c
k m
2
Forested area of watershed
50 100
150 200
250 300
350 400
450
Jan Feb
Mar Apr
May Jun
Jul Aug
Sep Oct
Nov Ra
in fa
ll mm
Month
Bogor, 21-22 October 2015
294 The highest low flow does not occur in the watershed with the largest percentage of forests
area, but in the watershed with 74 and 80 forest area. This can be seen in all measurement. Positive relationship between the percentage of land cover with the base flow rate is in line
with the results of research Price and Jackson 2007. This relationship pis associated with the high rates of infiltration under forest cover there by improving sub surface flow and base
flow. However, after the percentage reachess 74 and 80, the base flow decline. It can be assumed that forest cover affecting base flow from the evapotranspiration factor.
Evapotranspirationof forest trees can reduce the infiltration level there by lowering the base flow. High-density vegetation such as forests and grasslands have a strong influence on
evapotranspiration Gong, Lei, Yang, Jiao, Yang, 2014. The influence of evapotranspiration is very dominant especially in the dry season when rainfall is low
Dvořáková, Kovář, Zeman, 2014. Generally, plantations forest tend to reduce the average annual discharge, while the agricultural land tends to reverse Stehr, et al., 2010.
The positive correlation between the low flow with teak forest area is in line with the results of Pramono and Wijaya 2013 which concluded that the more extensive the percentage of
pine forest in a watershed the greater the low flow during dry season. The percentage of pine forest area influnces low flow 33.2 to 66.8. Since there is a big difference in the level of
influence of forest egetation typeson the low flow, it implies that the reforestation should be noted that tree species matching should consider rainfall. The magnitude of this effect will
have an impacton water availability, especially in the dry season. Selection of tree species will affect either during logging afforestation or at the time of reinvestment reforestation
Wang, et al., 2008. 3.1.4
Water quality
3.1.4.1 Turbidity
The clarity of water decreased due to the presence of these suspended particles deposited in water. This is resulted from eroded fertile agriculture land and also household’s waste water.
Inappropriate agricultural practices in some areas may led to soil erosion and have polluted rivers and groundwater. Figure 14 shows the higher forested area the lower its turbidity. In
other words, the lower the non-forest area, the higher its turbidity.
Figure 14: The relationship between turbidity and forested area 3.1.4.2
Biological Oxygen Demand BOD and Chemical Oxygen Demand COD BOD decrease when the forested area increase, or in other word increasing non forested area
will increase BOD. In line with Figure 15, a large amount of organic materials will result in explosive microbial activities and depletion of oxygen concentration then BOD become
2 4
6 8
10 12
14 16
20 40
60 80
100 T
u rb
id it
y NT
U
Forested area of watershed
Bogor, 21-22 October 2015
295 higher. Organic materials might be Organic pollutants comes from domestic sewage raw or
treated, urban run-off, industrial activities and farm wastes.
Figure 15: The relationship between BOD and forested area. Similar to those of BOD, COD is a test to determine oxygen needed by oxidant to oxidize
organics material in water. COD will decrease when forested area increases Figure 16. The demand of oxygen increases as the organic materials to be oxidized increases.
Figure 16: The relationship between COD and forested area
Figure 17: The Relationship between TDS and Forested Area
0.5 1
1.5 2
2.5 3
20 40
60 80
100 B
O D
mg l
Forested area of watershed
2 4
6 8
10 12
14
20 40
60 80
100 C
O D
mg l
Forested area of watershed
500 1000
1500 2000
2500 3000
3500 4000
20 40
60 80
100 T
DS mg
l
Forested cover watershed
Bogor, 21-22 October 2015
296 3.1.4.3
Total Disolved Solid TDS Figure 17 shows indirectly that the more forested area the lesser the TDS. This condition is in
line with the fact that primary sources for TDS in waters are agricultural and residential runoff, leaching of soil contamination and point sourcewater pollution discharge from
industrial or sewage treatment plants. Runoff contains of chemical material such as calcium, phosphates, nitrates, sodium, potassium and chloride which are dissolved from those
pollutants The chemical materials content such as pH, Mangan,Chlorine, Fluorine, Sulphate, Nitrite and
Nitrate in the study area are in the same pattern with TDS is shown in Figure 18.
Figure 18: The relationship between some chemical materials and forested area The relationship between TDS and others chemical contents is in line with the fact that
primary sources for TDS in waters are agricultural and residential runoff, leaching of soil contamination and point source water pollution discharge from industrial or sewage treatment
plants. Runoff contains of chemical material such as sulphate, nitrites, nitrates, natrium, and organic matters. In agriculture non- forested area the application of inorganic fertilizers tends
to delivers highly concentration of nitrates. In addition the well-drained area contained the
0,05 0,1
0,15 0,2
0,25 0,3
0,35 0,4
0,45
20 30
40 50
60 70
80 90
100 NO
3_ N
mg l
Forested area of watershed -0,05
0,05 0,1
0,15 0,2
0,25 0,3
20 30
40 50
60 70
80 90
100 NO
2_ N
mg l
Forested area of watershed
5 10
15 20
25 30
35 40
20 30
40 50
60 70
80 90
100 Su
lp h
at mg
l
Forested area of watershed 0,05
0,1 0,15
0,2 0,25
0,3 0,35
20 40
60 80
100 F
lu o
rin e
mg L
Forested area of watershed
500 1000
1500 2000
2500
20 40
60 80
100 C
h lo
rid e
mg l
Forested area of watershed
Bogor, 21-22 October 2015
297 highest concentration of nitrates Coulter, Kolka, Thompson, 2004; Hamilton Helsel,
1995. Moreover, water from forest area is low in nitrates compared to those from those from farmland, and residential Ngoye Machiwa, 2004.
Water quality observed is affected mostly by agriculture and urban activities, such as intensive agriculture, applying intensive tillage and sewage from settlement. This effect may come
through runoff and erosion from un-forested area to the river. Surface-runoff, stream flow and overland flow in natural waters also increase the turbidity levels in water. Tillage erosivity
increases exponentially with tillage depth. Therefore reducing tillage depth can therefore be considered as an effective soil conservation strategy Oost, Govers, Alba, Quine, 2006.
Turbidity will further influent the other water quality parameters such as BOD, COD and TDS. Gandasecaet al. 2011 revealed that the higher level of COD indicated the higher
pollution of water while lower level of COD indicated low level of pollution of water. BOD value will rise when there is more organic matter such as leaves, wood, wastewater or urban
storm water runoff took place at the river water. In the study area, it seems that the forested area reached 60 of the watershed, the parameters of water quality such as Sulphat, Chlorine,
TDS, and turbidity become almost constant. Forested area has function in maintaining water quality in the way of protecting land from
runoff and erosion. As it is stated by Gundersen et al., 2010, they explained the function of riparian forest RF. RF can reduce the C export to water bodies and forest buffers are
effective in protecting water quality and aquatic life, particularly when broader than 40 m. Furthermore riparian forests are highly valued for maintaining water quality through the
retention of sediments and nutrients. Fragment size or riparian forest length, riparian forest width and vegetation type, and fragment location in the catchment may have critical roles in
enabling forest fragments to reset the negative impacts of agriculture Harding, Claassen, Evers, 2006.
Moreover, forestry practices can be functioned as buffer region in urbanizing watershed as mentioned by Matteo et al.2006 which are to protect and to improve water quality. The
urban forest cover was shown to have substantial benefits to water quality and water quantity at a watershed scale. It was observed that pervious cover reduced the problem of nonpoint
source pollution from sediment and nutrient loading in urbanizing watershed systems. Combining riparian and roadside buffers for urban forestry can provide substantial
improvements to water quality. In addition, runoff decreased under these spatial policies, thereby mitigating storm water problems. But the forest area and forest distribution should be
compact and extensive, because fragmented forest of 5
–7 ha, located in the lower reaches of the catchment cannot mitigate the negative upstream effects of agriculture on stream
functioning Harding, et al., 2006. Based on Government Regulation Number. 82 2001,river water in the study area are mostly
suitable for fishery, livestock and irrigation Appendix 1, while Modang, Cemoro and Kejalen Sub Watershed are also suitable for drinking water Class I. These three sub watersheds are
covered by 91.9, 91.6 and 81.8 respectively. Factors that make water in the observed area are not suitable for drinking water are BOD, COD, TDS, Nitrite NO2 and Chlorine.
Nitrite and Chlorine are harmful chemical components. The greatest use of nitrates is as a fertilizer. Once taken into the body, nitrates are converted to nitritesEPA, 2012. In drinking
water, nitrite can cause severe illness with the symptoms include shortness of breath and blue baby syndrome. Whilst Chlorine is used widely in the manufacture of many products and
Bogor, 21-22 October 2015
298 items directly or indirectly, i.e. in paper product production, antiseptic, dyestuffs, food,
insecticides, paints, petroleum products, plastics, medicines, textiles, solvents, and many other consumer products. It is used to kill bacteria and other microbes from drinking water
suppliesLenntech, 2012 and it is carcinogenic to human body EPA, 2000. The process of removing these undesirable chemicals, biological contaminants and suspended
solids then is needed to produce water fit for human consumption drinking water. In general the methods used include physical processes such as filtration, sedimentation, and distillation,
biological processes such as slow sand filters or biologically active carbon, chemical processes such as flocculation and chlorination and the use of electromagnetic radiation such as
ultraviolet light.
4. CONCLUSION
