Evaluation of an Urban Drainage Channel System on Tuamang Road, Medan

. The population that continues to grow every time affects the total wastewater that is accommodated and channeled by drainage. This study aims to evaluate the existing condition of drainage dimensions on Tuamang Road, Medan. To determine whether the drainage can still channel the design wastewater discharge for the next 10, 20, and 30-year return periods or if it requires re-planning. The descriptive-evaluative method is used to evaluate drainage with stages starting from collecting data on population, annual rainfall, and measuring the dimensions of drainage channels; hydrological analysis, population projections for 10, 20, and 30-year; and evaluation of drainage channels. The research location is on Tuamang Road with a length of 1,200 m from Domestic House No. 130 to No. 101. The drainage system on Tuamang Road can still channel rainwater runoff and household waste for up to 10-year, based on analysis. 20 and 30-year, the dimensions must be enlarged to 1.0 m (bottom width) and 0.7 m (wet height of the channel). Cleaning sediment at the channel bottom must continue regularly to ensure the drainage system is working properly.


Introduction
Medan is the capital city of North Sumatra Province, Indonesia, which is the third largest metropolitan city in Indonesia and is one of the centers of economic growth. Due to transmigration and urbanization, the city has grown rapidly in the last decade. Compared with data in 2010, the population of Medan has increased by almost 340,000 people, or an average of 15,000-20,000 people/year [1]. Based on global population projections, it is predicted that the previous figure will continue to increase even until 2030. The population density of 9,000 people/km 2 is very large compared to the average population density of Indonesia, which is only 161 people/km 2 . Medan Tembung is the sub-district with the sixth largest population out of a total of twenty-one sub-districts in Medan, which will be more than 146,000 people in 2020. Its location in the city center contributes to the success rate of regional management in Medan.
However, on the contrary, these facts bring new problems that have not been completely addressed. The massive reduction of environmental degradation factors due to the expansion of domestic land causes the impermeable surface to become wider and changes the natural hydrological cycle, which in fact, disrupts the functioning of the drainage system [2] [3] [4].
Extreme rainfall can cause massive flooding and paralyze a city, causing economic losses [5].
The problem that often occurs today is the ineffective dewatering process after the rain occurs due to changes in land use and outside the existing drainage capacity [6]. The drainage system must be able to reduce or divert excess water in an area. Providing adequate and integrated drainage channels in an urban drainage system is an absolute necessity. Most cities in Indonesia, including Medan, design drainage to drain rainwater into water bodies (runoff) as quickly as possible. Urban drainage fills up faster due to a large volume of water being collected at the same point. In contrast, the capacity of drainage tends to decrease due to erosion and sedimentation. Drainage systems that do not function properly can cause flooding [7]. Potential failures of urban drainage systems are generally caused by: (a) functional failure due to hydraulic overload on the system, for example, due to extreme rainfall, excessive infiltration, and (b) structural failure due to malfunctioning component systems [8]. In 2022, the flood disaster in Medan was recorded to have inundated 56 urban villages, with 4,306 families affected [9] [10]. This incident not only resulted in great financial losses reaching Rp. 26 billion, but the worst flood also caused the death of 3 people and the death of dozens of residents' livestock [11]. In the face of urban growth, urban planners have challenges to the demand for urban drainage infrastructure services that need to be improved. Drainage channels are very important for managing rainwater runoff and protecting road structures, so it is necessary to evaluate and maintain drainage systematically [12].
The same research study has been conducted to evaluate the urban drainage system. Sibagariang & Saputra [13] only evaluate the 10-year condition with a limit of 2005 to 2014 in a 5-year return period in Medan; Nusantara [14] examines the capacity of drainage channels to cope with flooding, not predicting certain return times in the evaluation of drainage channels; Putri [15] evaluated the urban drainage system with only a five-year return period. According to the researchers, the methods used in previous studies were deemed to be less extensive. Because drainage system concept in Indonesia is generally done with a hybrid system, this study was carried out by considering the generation of domestic wastewater and runoff during the rainy season. Therefore, researchers aim the evaluation of urban drainage on the ability to accommodate terrestrial runoff and domestic wastewater in the next 10, 20, and 30-year on a systematic basis. Hopefully, this research can be useful input for the government, especially Medan city Stakeholder, in improving public facilities and infrastructure related to people's livelihoods.

Research Location
This research was conducted on Tuamang Road, Medan Tembung District, Medan, North Sumatra. This area is one of the densely populated areas, and almost the entire area is built-up land. Its location, on the border of Medan and Deli Serdang Regency, makes this area very strategic near a complex of public and private universities, one of which is the Universitas Negeri Medan. So, that many students come to live; in boarding house businesses, housing complexes; as well as places of business selling, such as cafes and food stalls.

Collecting Data
In this study, two sources of data were used: primary and secondary. Primary data collection was carried out by observing the research area, identifying the drainage channel's existing condition and the channel's dimensions, interviewing the estimated number of households in the location along the drainage channel, and conducting interviews with residents about the drainage condition. Secondary data collection was obtained from the results of a literature review in the form of rainfall data from Sempali Climatology Station, Medan (Table 1).
Secondary data was also obtained through literature studies related to the analysis of drainage channel capacity. The amount of wastewater that the canal can hold is calculated using the dimensions of the current drainage system. Based on the discrepancy between the actual drainage volume and the sediment volume, the dimensions of the current drainage are established. As part of the appraisal process, this information becomes crucial. In this investigation, measurements are taken at ten separate places, each of which is 12 m apart, to estimate the actual drainage dimensions. Because it is integrated with the residents' yard, the amount of points takes into consideration where there is a physical change in some areas of the channel. To lessen odors and the development of mosquitoes, some locals convert the canal into a closed canal, which makes measuring the canal impossible. The same spot where drainage volume is really measured also serves to measure sediment volume.

Projected Population Growth
The number of residents is taken into account to calculate the total production of domestic The geometric population projection approach makes the premise that the population will grow measurably based on multiple analysis. Every year the population growth rate is considered the same. Population growth in the-n (Pn) using the geometric method is determined by the equation Pn = P (1 + r). Where, P0 is the population data for the final year, r is the rate of population growth in the study area, and n is the number of base intervals with the nth year.

b) Arithmetic
Population projections using arithmetic method assume that the annual population growth will be constant, which is calculated by the equation Pn = P0 (1 + r n).

Hydrological Analysis
The hydrological analysis is the stage of processing rainfall data which is then compared to the volume of drainage channels to know the intensity of rainfall and the estimated volume of rainwater flowing into the drainage as runoff.

a) Frequency of rainfall
Analysis of the frequency of rainfall in the next 10, 20, and 30-year using the Gumbel and Log Pearson III Distribution methods [16].

1) Gumbel
The calculation of rainfall in the return period T year (Xt) using the Gumbel method is . Where, I is rainfall intensity (mm/hour), R is design rainfall (mm), and t is rainfall duration (hours).

c) Runoff flow rate
The planned runoff flow rate is sought using the rational method because this method is suitable for the condition of the drainage area, which is not too wide, and the rainfall is considered uniform. The sensible method has an equation, namely Q ch = 0,278 CIA. Where 0.0278 is the correction factor, C is the coefficient of runoff (0≤C≤1), I is the rainfall intensity (mm/jam), and A is the channel area (m 2 ).

d) Domestic wastewater flow rate
Domestic wastewater flow rate is the amount of discharge from household activities that are channeled into drainage channels. The amount is largely determined based on the number of people per dwelling, type of activity, economic level, and type of dwelling. According to Sutjahjo [17], the consumption of clean water for the category of one-story housing with a building area of less than 90 m 2 is 150 L/person/day. The waste generated is around 80% of the total amount of clean water consumption.

Existing Volume of Drainage
At the research location along Tuamang Road, there is a tertiary channel. This channel uses a square type, as shown in Figure 2.

Domestic Wastewater Flow Rate
Based on data obtained from the Sidorejo sub-district office, the number of houses located on  Table 2.  [17].
Based on field data results, houses located on Tuamang Road along 1,200 m on the left are, on average, a medium-type house buildings with type I. For this building, the amount of clean water consumption, according to Sutjahjo [17], is 150 L/person/day. Eighty percent of them will be released back into the environment in the form of wastewaterwater. The production of domestic wastewater is largely determined by the number of people living in an area. The estimated amount of domestic wastewater in 2022 that is channeled to the drainage on Tuamang Road is as follows:

Hydrological Analysis
Rainfall data for the last ten years, obtained from Sempali Climatology Station, is used to project future rainfall intensity. Rain intensity (mm/hour) each year can be seen in . Where, R24 is the rainfall in 24 hours and t is time [18].   To calculate the design channel discharge (Q, m 3 /day) the equation Q = 0.00278 CIA is used.

Drainage Plan Dimensions
Based on Rabori & Ghazavi [22], the design channel dimensions are calculated based on the discharge that must be accommodated by the channel greater than or equal to the design discharge caused by the design rain (Qplan ≥ Qflow). From the design discharge obtained, namely m 3 /s, the dimensions of the channel design can be found, where the roughness coefficient n is 0.016, and the slope of the channel base is assumed to be 1:1000. Thus, the dimensions of an economic drainage channel determined as follows:  [26] to the local community is to be diligent in cleaning the sediment or sediment at the bottom of the drainage by dredging so that there is no excessive deposition that can reduce the drainage capacity.

Conclusion
Based on the evaluation of the drainage channel on Tuamang Road starting from domestic house no. 130 to no. 101, the channel is still safe for flood discharge with a planned return period of 10-year. On the other hand, other periods must be re-planned because the capacity does not meet the planned flood discharge. For the re-planning of the drainage channel, a 30- year re-planned flood discharge was used because, in addition to producing a larger capacity, its dimensions were not much different from the channel capacity that used a 10-year flood discharge. In the future, there is hoped that research will discuss design evaluation in Medan City with a sustainable paradigm that uses a separate system.