RESULT AND DISCUSSION 1 Precipitation
Bogor, 21-22 October 2015
704 Information :
V = water volume in the collector cm
3
D = water level in the collector cm A = cross-sectional area of collector cm
2
Water volume in collector II was also measured as same as collector I, then the total volume were found out with formula:
Vt = V1 + n x V2
..λλλλλλλλλλλλ.......λλλ..λλλλ2 Information :
Vt = total of water volume V1 = water volume in the collector I cm
3
V2 = water volume in the collector II cm
3
n = number of hole in collector I, that were 12 holes
Total water volume then was converted to m
3
hamonth. Soil erosion was observed by taking water sample from each collector as much as 100
ml. Before water sample were taken, the water and the sediment on the bottom of the collectors were stirred well, then the water sample were strained with strain paper. Dry
weight of strain paper was previously known. Then, strain paper and the sediment were dried in an oven with temperature of 105
o
C then the weight was measured. Weight of eroded soil were analysed by formula:
W
tc
= W
1
+ W
2
...λλλλλλλλλλλλλλλλλλλ........λ..3 Information:
W
tc
= weight of eroded soil g W
1
= weight of soil sediment in collector I W
2
= weight of soil sediment in collector II W
1
or W
2
= V
d
V
s
x W
kse
– W
ks
V
d
= water volume in the collector liter V
s
= strained water volume liter W
kse
= weight of strain paper together with the soil sediment g W
ks
= weight of strain paper g
Water yield was measured by river flow measurement station with automatic water level recorder. Suspended load of river water were done by water sample taken from river flow
measurement station and analyzed in laboratory.
3. RESULT AND DISCUSSION 3.1 Precipitation
Precipitation is an inflow in hydrological cycle. Precipitation data can be seen in Table 1. Table 1 showed that precipitation in year 2013 was higher than that in 2014.
The average precipitation in 2013 was 281.588 mmmonth. While in 2014 was 207.13 mmmonth. The
low average precipitation in 2014 was caused by a long dry season on August to November. The lowest average precipitation was on September that only had two days of rain.
Precipitation is an inflow in hydrological cycle. Precipitation rate will affect other hydrologic parameters. Precipitation has a positive correlation with erosion, it means the higher
precipitation, the higher erosion could happen. Similarly with surface runoff, the higher precipitation, the higher surface runoff potentially to happen.
3.2 Erosion The erosion measurement is presented in Table 2. Table 2 showed that the erosion in plot 1
and plot 2 were different due to the different condition of the plot. Comparing Plot 1 and
Bogor, 21-22 October 2015
705 Plot 2, it showed that soil erosion in Plot 1 was lower than that on Plot 2. It was caused by
the difference of land cover. In Plot 1, soil surface under meranti stand was covered by undergrowth plants and litters. While in plot 2, soil surface was covered by Imperata cylindrica
and undergrowth plants, no litter. In 2012, when plots had just been made, erosion in plot 2 that had Imperata cylindrica cover was lower than Plot 1 that did not have any surface cover. In
2013 and 2014, erosion in Plot 2 was higher than that was on Plot 1. The soil surface of Plot 1 had been covered by undergrowth species and litters, while Plot 2 covered by Imperata
cylindrica. Table 1: Precipitation data of Jupoi watershed
No. Month
Precipitation mm Year 2013
Year 2014
1. January
287 208
2. February
369 183
3. March
337 307
4. April
410 510
5. May
258 201
6. June
160 112
7. July
419 107
8. August
125 43
9. September
94 31
10. October
168 30
11. November
532 399
12. December
220 354,5
Sum 3379
2485.5 Average
281.58 207.13
Table 2: Erosion under meranti stand in Austral Byna concession
No. Month
Total volume Plot 1 kghamonth
Total volume Plot 2 kghamonth
Year 2013 Year 2014
Year 2013 Year 2014
1. January
32.17 28.26
29.13 26.96
2. February
36.52 15.22
34.35 19.13
3. March
60.43 38.70
56.09 31.30
4. April
150.87 53.04
218.26 57.39
5. May
41.74 17.39
50.00 20.43
6. June
16.52 8.26
10.43 16.52
7. July
34.78 8.7
38.26 12.17
8. August
13.48 3.04
7.39 6.52
9. September
10.00 6.09
1.30 7.39
10. October
10.87 3.04
13.48 3.91
11. November
41.74 20.43
47.83 23.48
12. December
41.30 34.35
33.04 46.52
Sum 490.43
236.52 539.56
271.73 Average