Analysing the drainage system using epa swmm 5 . 1 ( study case : jababeka ii industrial , cikarang baru , bekasi regency )

Received 15-09-2020 Revised 17-10-2020 Accepted 11-12-2020 Available online 15-12-2020 Abstract. Due to the data in 2030, the urban growth in developed countries is 83%, and developing countries is 53%. Jababeka II Industrial Estate is one of the urban industrialization located at Bekasi Regency. In its development, the consideration of drainage facilities is one thing that needs. Because with its function as a channel that carries runoff water to rivers/lakes/reservoirs to avoid flooding. Objectives: This study aimed to know the existing condition of the drainage system and the water balances in the form of runoff in Jababeka II Industrial Estate by the simulation of SWMM 5.1. Method and results: The process of this research used a quantitative method, and the data collection method used secondary data, include the information from existing drainage system with precipitation event in 12 years (2009-2020) are obtained from the WTP Jababeka Residential, drainage dimension, and masterplan of Jababeka II. To calculate rainfall planned used a fifth-year return period based, it's on the city's classification under study. The probability distribution method uses Log-Pearson III with a planned rainfall of 128.22 mm/d and the highest rainfall intensity of 54 mm. Based on the simulation results, it was found that the Jababeka II Industrial Estate contained puddles in several channels. The peak was at the 3rd hour of the simulation, which were 19 channels. It's influenced by the type of soil that is quickly saturated. Conclusion: The simulation of the existing condition at Jababeka II has the highest runoff at the 2nd hour of simulation, and floods occurred in 19 channels. It's affected by the impermeable sub-areas. The water balance result is the amount of precipitation 128.22 mm with the intensity is 54mm due to 5 years of forecasting, thus producing the outflow is 128.511 mm. Therefore the number of continuity errors of a surface is -0.227%. Keywords


Introduction
Human activities significantly disrupt the natural hydrological cycle's quantitative and qualitative parameters. The statistics data are shown data 83% of developed worlds and 53% of developing societies predicted to live by 2030 in urban areas.
Urban growth continues to occur in developing countries on broad spatial scales, with whole cities often built in a short time [1]. This change affects the function of the land where the water absorption area is reduced. The waterways' number and dimensions changed so that water infiltration reduces, and flooding is commonly occurring [2]. The UNESCO Press Paris in 1974 has mentioned the industrialization include in urbanization [3]. It can be considered human activities involving changes in land tenure and land use resulting from rural land conversion to industrial use and urban, suburban, and industrial communities. Surface runoff directly can convert from more than 40% of rainfall in urban areas with more than 50% of impervious surfaces 4]. Thus, a drainage system must be supported to prevent flooding due to flow exceeding the channel capacity.

Natural Catchment
Urban Catchment Fig 1.Volumetric hydrological process diagrams for natural catchment and urban catchment [5].
Jababeka Industrial Area, located in Bekasi Regency, is urban industrialization, which continues to grow. Therefore it is necessary to update the existing channel This study analyzes the drainage channels in the Jababeka II Industrial Estate at a time of maximum rainfall for the last 12 years. Thus, this research has two purposes knowing the Jababeka II Industrial Estate water balances in the form of runoff during the simulation and knowing the flood occurred in the existing condition of drainage system using a simulation of SWMM 5.1.

Research Location
The research was carried out from May to July 2020 during the dry season, located at Jababeka II Industrial Estate, Cikarang Baru, Bekasi Regency ( Figure 2). The drainage system is used to collect rainwater and go to Cilemahabang River. The channel's location is along the shoulder side of the road with several dimensions that depend on the elevations.

Population and Sample
Population and sample are an essential part of a study where a community is a unit of individuals or subjects in the area and time with a certain quality. The research sample is part of the people used as the research subject as a representative of the population [15]. In this study, the community is the drainage system from the entire Jababeka Industrial Estate. At the same time, the sample used is the drainage system in the Jababeka II Industrial Estate with a maximum daily rainfall for 12 years, 2009 -2020, as measured in the sample. Sampling using the purposive sampling method or judgment sampling is the choice of participants who deliberate because of the participants' quality and criteria. It's a non-random technique that does not require an underlying theory or some participants but is based on the researcher's sample criteria to achieve a specific goal [14]. Based on this study's standards, the sample taken was determined by the frequent flooding in the Jababeka Industrial Area and the maximum rainfall over the last ten years.

Tools and Materials
This study uses secondary data collection methods, which are collected from Jababeka WTP Residential. They are channel dimension, the water flow direction, topographic maps, masterplan of Jababeka II Industrial Estate drainage system, and the daily rainfall intensity data from 2009 -2020. The tools used during this research were a laptop, stationery, calculator, Google Earth software, TCX Converter, Quikgrid, QGis, AutoCad, and SWMM 5.1.

Research Procedure
In the research procedure, there are several steps to get the data. They are frequency analysis of hydrological data, rainfall distribution, discharge channel capacity calculation, and the % impervious and %pervious [16]. The frequency analysis of hydrological data is the value of rainfall planned or equal to the definition of maximum probability of rainfall intensity with forecasting in the next few years, where it depends on the requirement. Then the result will be times with rainfall distribution according to the previous research. And the final product will become the time series. Continue to calculate the discharge capacity using manning's equation.
After getting the time series and the flowrate of discharge capacity, determine the %impervious and %pervious.
Below are the following data processing procedures were applied: ii. Testing the Suitability of Frequency Distribution The frequency distribution that set should be tested using the suitability of frequency distribution testing. There are two distribution tests: the first is the chi-square test (1) and Smirnov-Kolmogorov (2) [18].
The planed rainfall value can be calculated after determining the frequency distribution to be used. Nevertheless, SWMM 5.1 claims that the rainfall value is a constant value that uses time series to continue over a given recording period for rainfall measurements. So what is calculated in the other SWMM 5.1 timeseries is between the reported values [11]. In this case, the rain distribution value derived from the literature can be used as a time series for modeling [13].

c. Discharge Channel Capacity
Data needed for the addition of discharge outflow (initial flow) from the runoff into the channel uses Manning's equation (3) [8]: The method of infiltration calculation used for modeling is the Horton method. Based on the interpolation of observations, the infiltration decreases exponentially from the initial maximum to the minimum rate during extended rainfall. The required parameters include the maximum and minimum infiltration rate, the decay coefficient, which describes how fast the rate of decay over time, and the time it takes for the saturated soil to dry again completely. After ensuring that all the required data is entered into the modeling process, the modeling can be started [11]. Two problems occur in Jababeka II Industrial Estate, first is due to a small size of absorption caused by the limited green surface, shown in Figure 6. Lastly, because Jababeka II has saturated soil, which easy to be watered, this affects the earth's character at the time of infiltration due to observation results.

Result of Frequency Analysis of Hydrological Data
Rainfall analysis is carried out using daily rainfall data from 2009 to 2020, belonging to the WTP Jababeka Residence. Plan rainfall is calculated based on the 12-year daily rain, as shown in Table 1. In the hydrological analysis, a frequency analysis is used to estimate the maximum probability of precipitation during a given period. The frequency analysis results serve as the basis for calculating the anticipation of any likelihood of occurrence. Rainfall data from rainfall recording stations around or near study sites are hydrological data required for drainage design [12]. Frequency analysis can be carried out using four probability distribution methods shown in Table 2 along with 2, 5, 10, and 50-year rainfall and return period.  The time scale used to calculate the planned precipitation is 2, 5, 10, and 50 years. Return time is the estimated time at which a certain amount of rain is equal or exceeded.  Table 3. The results of the calculation of the Chi-Square Log Pearson III distribution are shown in Table 4.

Result of Rainfall Intensity Calculation
The hourly rainfall distribution was used based on the distribution obtained by Fajri (2009) [13], as shown in Table 5. The value of rain distribution is used as a bulk time series plan for SWMM 5.1 model. The first hour has the highest percentage of the peak hour simulation to have a significant runoff potential.

Result of Hydraulic Analysis on Existing Channels
The hydraulic analysis is carried out to determine whether the planned drainage system is following the requirements. This analysis includes the calculation of existing channel capacity and channel planning. Table 6 shows the results of the hydraulic study. The following Table 7 presents the results of the analysis of hydraulic discharge and hydrological discharge for the five year return period. The hydraulic analysis results are accepted because the hydrological capacity is smaller than the hydraulic capacity.  Table 8 shows the subcatchment parameter values, which consist of areas of subcatchment, length, and size. This width came from an average of the total length, percent of the impervious and pervious area. The value of the impervious percentage depends on the impermeable site on subcatchment. Other than that, it also represents the result comparing the subcatchment area with impermeable subarea.

The Analysis of Simulation Model
The drainage simulation network in the study area was carried out using SWMM Status report from the simulation showing the continuity error value is 8.98% for flow routing and -0.23% for surface runoff. SWMM 5.1 simulations have a validity number of continuity errors of less than 10%. If more than 10%, then the simulation analysis must be doubted [11]. The results of the change can, therefore, be accepted. C96, C97, C103, C114, C115, and C123. As shown in Figure 9, the runoff water will peak in the second hour. In the time series case, this is influenced by the soil nature area and the second factor of flooding in which the soil type is saturated. So that in the first hour, the land is dry. The ground can then absorb rainwater, but in the next hour, the soil will be saturated and become runoff water.  The graphic from Figure 9 is shown the condition that happened for 6 hours.
There are four subcatchments taken as the representative of runoff during the simulation. Green-line is the highest than the others following to the area of subcatchment, while the red-line is the lowest because the site is the small as well, for blue and purple-line are taken from random subcatchment. However, the whole four lines have the same graphic shape. Even the area of subcatchments is different, where it shows that the amount of runoff has a linear relationship with the subcatchment area. Fig.10. The condition of C88 profile of channel traffic. Figure 10 shows the state of the C88 channel flooded due to the amount of runoff discharge so that the channel's capacity is not enough-the same as in Figures 6 and 7 for the red channels. According to the current condition result, it can be seen that there is an imbalance in the water balance then resulting in flooding. The water balance of SWMM 5.1 is interpreted by a percentage of a continuity error, where it represents the differences between initial storage + total inflow and final storage + total outflow. Table 9 has shown the status report from simulation results in Jababeka II Industrial Estate, with the number of precipitation is 128.22 mm. As a result, the continuity error for surface runoff is -0.227% came from total outflow that consists of rain rather than divided with total inflow consisting of evaporation, infiltration loss, and surface runoff, and final storage. The number of precipitation came from the rainfall planned (mm), which is the water source that enters the study area.
Meanwhile, the evaporation, infiltration loss, and surface runoff are the sources of runoff water.

Conclusion
The simulation carried out in Jababeka II Industrial Estate using SWMM 5.1, which showed that the highest runoff value occurs at the 2nd hour, which is influenced by a limited green surface. The total numbers of a channel that floods occurred during the 2nd hour are 19 channels with different channel sizes affected by land elevation. According to the water balances of rainfall planned, 128.22 mm, which is rainfall intensity 54 mm due to 5 years forecasting, and total outflow is 128.511 mm resulting continuity error of surface runoff is -0.227%.

Acknowledgment
Thank you to Dr. Ir. Yunita Ismail Masjud, M.Sc., who helped and guided through finish this research. As well as the WTP Jababeka Residence, who helped collect all data needed during this research. And also like to thank Mr. Rijal Hakiki S.S.T., M.T., which helped to do simulation modeling that could work well.