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Journal : Civil Engineering Forum Teknik Sipil

KAJIAN PERUBAHAN EROSI PERMUKAAN AKIBAT PEMBANGUNAN HUTAN TANAMAN INDUSTRI DI AREAL PENCADANGAN HTI KABUPATEN KETAPANG PROPINSI KALIMANTAN BARAT Saptarini N., C. Lestari; A. Kironoto, Bambang; Jayadi, Rachmad
Civil Engineering Forum Teknik Sipil Vol 17, No 2 (2007): MEI 2007
Publisher : Civil Engineering Forum Teknik Sipil

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Abstract

Allocated area for planted-forest in Ketapang Regency, especially in Durian Sebatang river basin and its surrounding are in critical condition with low land- productivity and poor hydrologic characteristic. These areas have to be conserved with vegetative method. One of the efforts to synergize soil and water conservation and economic interest is immediately to rehabilitate the critical areas with Planted-Forest (Hutan Tanaman Industri—HTI). Planted-forest system can be arranged to control the rate of erosion. The aim of this study is to predict the rate of erosion at the existing condition and the change of erosion rate at the planting-rotation system (cutting system) in the planted-forest of Acacia sp. The planting- rotations are 5 years, 6 years, 7 years and 8 years during the range of 11 years study. The research uses the version 3.3 of GIS Arc View program to make the land-unit map. The amount of surface erosion (sheet erosion) estimated base on the land-unit map. The calculation of the erosion rate uses the Modified USLE method (Snyder,1989), in which factors influencing the amount of surface erosion are Rain Erosivity (R), Land Erodibility (K), Length and Elevation of slope (LS) and Soil Conservation Factor and Planting System (VM). The results of the study show that the rate of erosion at the existing condition is 1,24 mm/year. Its a light danger erosion level, under the soil loss tolerance limits (2 mm/year). During the 11 first years of HTI development, the rate of erosion in planted forest with planting rotation of 5, 6, 7 and 8 years ranges from 0,91 mm/year to 2,66 mm/year. Its included in a very light to heavy erosion danger level. The lowest average erosion rate is found in the planting rotation of 7 year, continued by 8, 6 and 5 year. At first cycle, the rates of erosion in all planting rotation are more than the amount of existing erosion. Its caused by land clearing activity for plantation, but at further cycle, those are decrease until under the existing condition when the vegetation at conservation areas reach to an optimal growth. The rates of erosion in HTI can be controlled if we arrange the allocation of land utilization t consider by soil type. The reasonable planting-rotation of HTI with Acacia sp vegetation’s type to be applied in the research area is 6 years or 7 years. The optimal planting rotation is decided base on amount of erosion rate, soil stability, wood utilization and economic value. The expectation of this research can be contribute in soil conservation and social economic integrated development program.
HIDROGRAF SATUAN: PERMASALAHAN DAN ALTERNATIVE PENYELESAIAN Sujono, Joko; Jayadi, Rachmad
Civil Engineering Forum Teknik Sipil Vol 17, No 2 (2007): MEI 2007
Publisher : Civil Engineering Forum Teknik Sipil

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Abstract

Unit hydrograph is one of flood design method that commonly used in Indonesia. Problems emerge in the unit hydrograph application including high rainfall variability both time and space, lack of automatic rainfall data needed for unit hydrograph derivation. However, the output of the catchment system called hydrograph that represent all the phenomena in the system is available. So, effect of rainfall variability on unit hydrograph and the possibility to derive unit hydrograph based on hydrograph data without rainfall data need to be studied. Unit hydrograph derivation is done by using different rainfall input i.e. single station, rainfall catchment and inverse effective rainfall derived based on hydrograph alone. The resulted unit hydrographs are then used for design flood calculation. Results show that the resulted unit hydrographs vary among the different rainfall inputs. The difference in peak relative to unit hydrograph derived based on average rainfall for Bedog, Code and Winongo catchments could reach -18%, -30% and -11%, respectively. This result indicates that in the catchment studied, the rainfall variability is relatively high. However, the difference in flood peak is quite small, that is up to -12% for all the catchments. There is a trend that the station closest to the catchment centroid gives small bias in design flood relative to the design flood computed based on average rainfall.
KAJIAN PENANGANAN BANJIR KALI CILIWUNG DKI JAKARTA DITINJAU DARI ASPEK HIDRO-EKONOMI (STUDI KASUS PADA RUAS CAWANG – PINTU AIR MANGGARAI) Waluyadi, Heriantono; Jayadi, Rachmad; Legono, Djoko
Civil Engineering Forum Teknik Sipil Vol 17, No 3 (2007): SEPTEMBER 2007
Publisher : Civil Engineering Forum Teknik Sipil

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Abstract

Every year in a rainy season, flood inundates several areas along Ciliwung River, especially in the Cawang – Manggarai reach. Flood in this reach is caused by land use changing in upstream area and narrower the river width in the downstream area. Several planning will be implemented to reduce the flood, which are normalization with widening river, revetment and dike construction also diversion channel from Ciliwung River to East Banjir Kanal. To determine the benefit of every flood control structure the integrated and comprehensive considerations is required. The study of performance of flood management planning with hydro-economy approach that considers hydrologic, hydraulic and economic aspect is conducted in this study. The aim of this study is to determine the benefit of every flood control structure. Before determining the benefit of flood control structure, the expected annual damage must be calculated, the calculation is based on discharge-probability of exceedence curve, discharge-stage curve and stage-damage curve. The relation from above three curves will be needed for damage-probability of exceedence curve. As a result from this curve the expected annual damage and the benefit of flood control structure can be determined. The results of analysis are that the benefit of flood control structure for normalization, diversion channel with 2,5 m in width gate, diversion channel with 3,0 m in width gate and diversion channel with 3,5 m in width gate are Rp. 20 billion, Rp. 16.1 billion, Rp. 18.9 billion and Rp. 20.1 billion respectively.
STUDI ALTERNATIF PENGENDALIAN BANJIR SUNGAI TONDANO DI KOTA MANADO J.B. Nanlohy, Benjamin; Jayadi, Rachmad; Istiarto, Istiarto
Civil Engineering Forum Teknik Sipil Vol 18, No 1 (2008): JANUARI 2008
Publisher : Civil Engineering Forum Teknik Sipil

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Abstract

Tondano River, along with its tributary Tikala River, is very potential to cause flood in Manado City. There were three big floods occurred in 1996, 2000 and 2005. In order to mitigate the damage risk due to flood, the controlling effort that can be applied soon in the field is required through short term flood control plan using structural measures. The feasible alternative plans should be evaluated to define the best plan based both on the hydraulics point of view and their effects on the river uses. The study is carried out through the 5 year return period flood routing using the version 3.1 HEC-RAS software. The selected design flood hydrograph is obtained using Nakayasu Synthetic Unit Hydrograph method by elaborating design rainfall derived from partially series rainfall data frequency analysis of Tondano and Tikala watersheds. Flow simulation is conducted in steps by modeling the hydrograph from Tikala River as the lateral inflow. The first simulation is carried out using bank full capacity discharge to define the flood characteristic and the critical sections. The second simulation is carried out for the design flood hydrograph using unsteady flow calculation on each plan to study the hydraulics feasibility. The study conducted herein is elaborated on water surface profile and velocity due to the plans affectivity to carry-off the flood discharge safely as well as the effect on river uses.  Based on the existing condition simulation, result shows two reach critical sections of the right bank and one reach critical section of the left bank Tondano River. The results of flood control simulation indicate that there are no significant differences on velocity among plans, but there are disparities on the capacity to carry off flood discharge safely with no overtopping. For the normalization plan, the overtopping is occurred along the critical section, whereas for both dike plan and combination of dike and normalization plan, no overtopping are occurred but the the critical sections are still existed. Revised plans for dike and combination of dike and normalization are equally effective in carrying off flood discharge securely, but have different effects on water utilization during low flow period. Referring to the study result, the best alternative is the revised dike plan.
PENGARUH JUMLAH STASIUN HUJAN TERHADAP KINERJA METODE STORAGE FUNCTION DALAM PENENTUAN DEBIT BANJIR RANCANGAN Hari, Bambang Kuncoro; Jayadi, Rachmad
Civil Engineering Forum Teknik Sipil Vol 19, No 1 (2009): JANUARI 2009
Publisher : Civil Engineering Forum Teknik Sipil

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Abstract

Storage Function Method is a method applied in discharge calculation with consideration on catchments characteristics. This method is commonly used in Indonesia by the Japanese experts. The discharge calculation provided by the method is highly influenced by the catchments rainfall, thus the difference of rainfall station number will effect the accuracy of the calculation result. The objective of this study is to investigate the effect of difference in the number of rainfall stations on the value of model parameters as well as the accuracy of discharge calculation using the storage function method on Kali Madiun Basin. Basically, the concept used in the storage function method is a water balance, which is analyzed using the mathematical model. The data used in this research are the 10 days hourly rainfall during the flood, and the catchment characteristics constant as the model parameters. Using the trial procedure, the catchments characteristics constant as the input for each of the numbers of rainfall station (2;3;4;5;6; and 7 stations) will provide the 10 days hourly discharge, then the result will be calibrated to the observed data. Based on the calibration result, the smallest deviation of each rainfall station will be selected in order to identify the model parameter and to provide deviation of the observed data. The investigated deviation is the different value between the calculated and the observed runoff, includes volume deviation as well as the 10 days hourly discharge deviation, which are located at the control node of AWLR Sekayu and AWLR A. Yani. Based on the calibration results, it is shown that the largest volume deviation at AWLR Sekayu is 31.64% that occurs on 2 rainfall stations, while the smallest occurs on 6 rainfall stations with deviation of 17.43%. It is also shown that the largest discharge is 37.29% and occurs on 2 rainfall stations, while the largest and the smallest discharge deviations respectively are 36.7% that occurs on 2 rainfall stations and 26.39% that occurs on 7 rainfall stations. Based on the results, it is shown that although the largest number of rainfall station is not the most accurate, but in general, as shown in the graphical results, it is indicated that more numbers of rainfall stations tend to provide better accuracy.
KAJIAN PENANGANAN SEDIMENTASI DENGAN WADUK PENAMPUNG SEDIMEN PADA BENDUNGAN SERBAGUNA WONOGIRI Sardi, Sardi; Kironoto, Bambang Agus; Jayadi, Rachmad
Civil Engineering Forum Teknik Sipil Vol 18, No 3 (2008): SEPTEMBER 2008
Publisher : Civil Engineering Forum Teknik Sipil

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Abstract

High rate of sedimentation in Wonogiri Multipurpose Dam may cause the dam service period to become shorter than the prior plan. The discharge of Wonogiri Multipurpose Dam is an accumulation of inflow from several main rivers, including Keduang River which is located at the east side of the dam. Keduang River supplies very high sedimentation input to the reservoir. One of the steps studied and to be implemented in the sediment countermeasure was the building of sediment pocket dam in Keduang River mouth before it enters the reservoir. The research was conducted to determine the reservoir sedimentation before and after countermeasure through a mathematical model approach. It was done by doing flow and sediment transport simulation using the NCCHE-GUI Program to calculate deposition in the reservoir. Simulation was carried out in existing condition and the condition after the sediment pocket dam was built, with the assumption that discharge was evenly distributed for each month. This simplification method was applied in wich monthly simulation was done for one hour. Simulation result was then multiplied by the number of hours allocated per month to generate the result for one year period. Simulation result indicates that annually sedimentation reduction or net deposition is 30.41% in average after the treatment by sediment pocket dam. It is also identifed from the simulation result that the reduction is relatively small, since simulation was not performed up to the condition where the pocket dam was already filled up by sediment, in which the flushing process has not been optimally simulated.