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

40.87 19.71

44.96 22.64

Bogor, 21-22 October 2015 706 Based on corelation analysis, erosion and land elevation had a negative correlation, because soil erosion is influenced by several factors, such as land elevation, and vegetation. Land cover condition is the main factor inhibiting erosion Gintings, 2007. Erosion on Plot 1 and Plot 2 were lower than the allowable erosion. Generally, allowable erosion rate was 25 mmyear or equal to 25 tonhayear for mountain area or sloved area. For a flat area 0 σ5 it has been suggested as 10 tonhayear Sidle et al., 2004. Erosion rate on Plot 1 and 2 also much smaller than erosion in open area or plantation forests such as mahogany, agathis, puspa, cajuputi, mix stands and 13 years pine stand Kusmana et al., 2004. Table 3 below shows surface runoff data on both plots. Table 3: Surface runoff under meranti stand No. Month Surface runoff m 3 hamonth Plot 1 Plot 2 Year 2013 Year 2014 Year 2013 Year 2014 1. January 70.72 57.97 36.23 32.46 2. Februayi 83.18 10.14 54.78 12.75 3. March 114.19 25.79 61.44 20.87 4. April 154.77 124.63 88.11 77.67 5. May 71.88 16.23 42.89 16.52 6. June 61.73 5.51 34.78 11.01 7. July 98.83 5.8 57.97 8.12 8. August 12.17 2.03 11.30 4.35 9. September 8.12 4.06 8.12 4.93 10. October 9.56 2.03 14.49 2.61 11. November 43.18 35.94 57.97 34.49 12. December 28.69 22.90 23.48 31.01 Sum 757.02 313.02 491.54 256.80 Average

63.09 26.09

40.96 21.40

Table 3 showed that surface runoff on plot 1 elevation 24° was higher that that on plot 2 with elevation as 19°. It seemed that land elevation was run side by side with surface runoff. But when we look back to soil erosion. it showed that soil erosion was contrary with surface runoff. This fact was contrary to theory that said that the higher erosion. the higher surface runoff. Corelation analyses done to erosion and surface runoff said that correlation of both parameters were negative. This phenomenon happened because soil particles dispersion in plot 1 was hampered by undergrowth species and litters. so soil sediment that went into erosion drum become less. While in plot 2. rain impact to soil surface that covered by undergrowth and Imperata cylindrica was not hampered by any litters. so soil particle by splash erosion was carried by runoff. Erosion begins with splashing soil particle. When rain had flooding the soil. splash erosion will be less because critical depth for splash erosion is 3 mm. When water depth over that point. splash erosion will become minimum. But when surface runoff occurred. erosion will be dominated by soil dispersion process by surface runoff. Bogor, 21-22 October 2015 707 3.3 Water yield Water yield can be seen from water flow data of Jupoi River as showed in the Table 4. In 2014, the lowest water flow was on September and the highest was on April. While in 2013. Average water flow was 309.12 litersecond with the highest was on May and the lowest was on January. Water flow has a positive correlation with precipitation. The highest flow occurred on the highest precipitation vice versa. Table 4: Water flow of Jupoi River No. Month Water yield literdetik 2013 2014 1. January 54.74 385.58 2. February 184.33 146.02 3. March 209.67 658.12 4. April 183.20 1219.16 5. May 94.95 182.45 6. June 231.52 102.91 7. July 524.33 112.54 8. August 85.56 16.63 9. September 148.65 8.85 10. October 143.13 29.47 11. November 1429.60 337.26 12. December 419.70 168.61 Sum 3709.38 3367.61 Average 309.12 290.82 The peak flow flood data is needed to design flood control management system. While the lowest flow is needed for water allocation uses for many purpose. mainly in dry season. Average of yearly flow can describe water resource potency that can be use from a watershed. Measurement of water resource needs a more complex data related to population number. water quantity needed by the population to support their life and water supply. Jupoi river flow fluctuation was not too high. so the forest existence was assumed had a role in keeping water supply stability. Beside water level measurement. suspended load was also measured. The research showed that suspended load concentrated in Jupoi river water was very small and can be said as zero because water sample analyses said that suspended load concentrate in Jupoi river was zero. It happened because land cover in Jupoi watershed was still very dense. so precipitation in Jupoi river was not potentially erodable. The Jupoi river relatively good for daily consumption. as the water seemed clean. clear and colorless. Although it needs futher research for its chemical contents to make sure that the water is save for drinking water.

4. CONCLUSION