EVALUATION OF DRAINAGE CHANNELS ON RESIDENTIAL AREA

The incompatibility of construction of urban or residential drainage channels with design criteria is often found due to difficulties in designing drainage channels. designers often make design mistakes when designing drainage channels. This study aims to evaluate the drainage system and designs a drainage channel that can collect runoff discharge on Residential Area in Bekasi, Indonesia. The results of flood discharge obtained using the Gumbel method for the 10 and 25 year return periods are 298.78 mm and 370.38 mm. From the calculation of the channel capacity in the field and the discharge plan most of the existing channel capacity cannot accommodate the current planned discharge of 2.261 m 3 s -1 for the primary channel and 1.824 m 3 s -1 for the secondary channel. The current channel cannot accept runoff discharge during rain, so the channel rehabilitation plan is carried out by expanding and extracting the dimensions of the drainage channel.


Introduction
The drainage channel is a channel that serves to collect the flow and flow of rainwater and domestic liquid waste. The drainage channel capacity will determine the volume of water that can be collected and distributed to the drainage or water collection (Dewi Sartika T, Prastowo, & Pandjaitan, 2016;D. Sartika, 2016;T. D. Sartika, Prastowo, Pandjaitan, & Sitorus, 2017). If there is high rainfall, there will be water overflow. According to Lubis (Lubis, 2012) water flooding that occurs in a specific area shows that the standard capacity of the drainage canal has reduced due to several factors. Sartika & Ikotun | IJEAT 2(1);[39][40][41][42][43][44][45][46][47][48][49] IJEAT © 2019 www.Inter-Journal.nusaputra.ac.id/IJEAT 40 Factors that can cause a decrease in the drainage capacity includes maximum rainfall intensity, catchment area, and runoff coefficient. According to Kodoatie and Sugiyanto (Kodoatie, 2002), water discharge has not been a problem if it does not interfere with activities and it causes harm to human life. But if it has created a loss, then this problem must be addressed immediately. Therefore, planning a drainage system, especially in a residential area, needs to be given necessary attention, one of which is to deal with the occurrence of rainwater inundation.
Acceleration of development in urban areas will cause the water catchment area to decrease which will increase runoff discharge. The runoff would be a disaster if it balanced with the construction of proper drainage channels. From this condition, it is necessary to evaluate the drainage system and design drainage lines that can accommodate runoff discharge.

Data collection
The method of data collection consists of collecting data relating to the planning of drainage channels, namely: field observations, measurements, interviews, and data collection. The data needed is a maximum 10-year daily rainfall data from BMKG, hydraulic drainage design factor data, and drainage network data. Data for hydraulic drainage design factors are flow velocity, slope, roughness, flow depth, and size of the cross-section of the drainage channel. This data is obtained through primary data collection or in measurements and field observations. Data on drainage network obtained by plotting the data in the field, topography and land use.

Data Analysis
The initial stage of the research was carried out in the field of observation and tracking of channels in the pattern of drainage networks and measuring the dimensions of drainage channels (length, width, depth, slope, and embankment).
From this data, network drainage networks based on measurements (length, Before analysis of runoff discharge, it is known first when the concentration of rain then analyzed the intensity of rainfall using 10-year daily rainfall data using the Mononobe method. The maximum runoff discharge is obtained using the Rational method. From (Suripin, 2004), this method ware used limited to a relatively small watershed, which is a maximum of 300 ha. The feasibility of drainage channels will be evaluated using standard channel design criteria.

Characteristics of Research
The residential area is locate in Kaliabang Tengah, North Bekasi Regency which is between 6˚10'21,96'' to 6˚10'29,47'' South Latitude and 107.1'18,54'' to Based on observations in the field, the percentage of land is built more than vegetated land, so that rainwater is infiltrated to the soil a little and most of it becomes runoff. The rain which mostly falls to the ground without vegetation will be run down and flow towards the river so that the river flow increases rapidly.
According to Yin, H, et al (Yin, Zhao, Wang, Xu, & Li, 2017). runoff coefficient is an important parameter for the decision support of urban stormwater management.
Runoff coefficient is determined based on the land cover of water catchment area.
According Verrina et al. (Verrina, Anugerah, & Haki, 2013), topography, land use and soil type will affect the amount of runoff that occured in the area. Land cover in the Sanur Cluster consists of multi-unit houses/buildings, parks, and roads.
Land use type in the study location shown in Table 1.

Surface Runoff
According to Froehlich (Froehlich, 2010), the runoff discharge value was determined by the rain intensity that occurred in the region during the time of concentration, runoff area, and runoff coefficients. Drainage channel's runoff discharge at the study location with 3.39 ha area, the C value of 0.65.
When it rains with high intensity in residence will experience flooding on the main channel, and the cross section of the main channel is trapezium. The Sanur Cluster drainage channel is made using concrete with a smooth surface with a  Table 3.   If the estimated concentration time is less actual, the estimated peak discharge will be more effective than the cost of building an expensive drainage channel.
According to Suripin (Suripin, 2004), an area of <10 can be used for a return period of 2 years and on land 10-100 can be used for a return period of 2-5 years (Table 7). The water catchment area at the research location is 3.39 ha. Based on this reference in the design of primary and secondary drainage channels is 10 Sartika & Ikotun | IJEAT 2(1); 39-49 IJEAT © 2019 www.Inter-Journal.nusaputra.ac.id/IJEAT 46 years and 5 years. When it rains heavily, there will be a flood at the research site.
Based on the Central Statistics Agency 2019, the population of the city of Bekasi is 2,733,240 people. According to Susilowati and Santita (Susilowati, 2006), in Table   8, the re-planning period with a population of> 2,000,000 for primary and secondary channels is 25 years and 10 years.
Susilowati and Santita (Susilowati, 2006) states that rural/ suburban/ city/ urban areas use tertiary drainage systems and in the planning of the channels used is a 2-year return period (Table 8). Based on the results of the recapitulation of rainfall data in certain return periods in Table 4, it was known that the design discharge is 162.9 mm.  Table 9 shows the results of the design discharge analysis. In the plan for increasing drainage, the basic principle used is to maintain as many channels as possible. If not possible, changes will be made to the channel dimensions according to the planned flood discharge. According to Situmorang et al. (Situmorang & Nirmala, 2015), if the drainage channel capacity is higher than the planned flood discharge, the channel is still feasible, and there is no overflow of water. Handling flow discharge in a channel that has insufficient capacity is carried out by normalization (dredging of sediments), increasing channel height and making new channels.