Evaluation of Drainage Network System (Case Study of Pangkajene Kepulauan State Agricultural Polytechnic Campus Area)

The purpose of this research is to identify the condition of highway drainage channels and evaluate the existing highway drainage network system in accommodating runoff discharge, channel dimensions and flow direction in channels that occur inundation in the Pangkajene Islands State Agricultural Polytechnic Campus area which is expected to help solve flooding problems in the area. The research method used is descriptive quantitative, which is a method of calculation and description of the results of field data processing. Secondary data collection includes; rainfall data for the last 10 years, obtained from the Department of Resources; topographic maps, drainage network maps and situation maps, obtained from the Politani Pangkep Campus planning section. Primary data collection is obtained from direct measurements in the field using a Waterpass measuring instrument to measure elevation and channel length. The results of this study found that the drainage capacity < 2-year and 5-year return period Plan Flood Discharge, so planning is needed to increase drainage capacity

The purpose of this research is to identify the condition of highway drainage channels and evaluate the existing highway drainage network system in accommodating runoff discharge, channel dimensions and flow direction in channels that occur inundation in the Pangkajene Islands State Agricultural Polytechnic Campus area which is expected to help solve flooding problems in the area.The research method used is descriptive quantitative, which is a method of calculation and description of the results of field data processing.Secondary data collection includes; rainfall data for the last 10 years, obtained from the Department of Resources; topographic maps, drainage network maps and situation maps, obtained from the Politani Pangkep Campus planning section.Primary data collection is obtained from direct measurements in the field using a Waterpass measuring instrument to measure elevation and channel length.The results of this study found that the drainage capacity < 2-year and 5-year return period Plan Flood Discharge, so planning is needed to increase drainage capacity

INTRODUCTION
The word drainage comes from the word drainage which means to drain or drain.Drainage is defined as the study of efforts to drain excessive water in an area and a system made to deal with the problem of excess water both water above ground level and water below ground level, Excess water can be caused by high rain intensity or as a result of long rain duration (Yudi Mardiansyah, et al., 2009), In general, drainage can be interpreted as a series of water buildings that function to remove or reduce excess water from a place or land so that the land can be used optimally.
The Pangkajene Islands State Agricultural Polytechnic Campus, hereinafter referred to as Politani Pangkep, is located in Mandalle District, Pangkajene and Islands Regency.To the east of the campus location there are mountains and residential areas while to the west is directly adjacent to the Makassar Strait, with the location of the campus in the middle between the mountains and the sea, the campus area is openly a water overflow path if the drainage system is managed properly.
On February 13, 2023, there was a flood or inundation that was quite extensive and the height ranged from ± 20-30 cm in the courtyard of the rectorate building and its surroundings, resulting in disruption of comfort in activities in the campus environment, where in general the main causes of inundation are changes in land use, rainfall, inadequate drainage capacity and improper flood control system planning (Andrianto, J. et al., 2021) from the results of observations in the field In addition to sedimentation problems, damaged channel conditions are also one of the causes of inundation, inundation that occurs on the road surface, this can cause damage to road construction.Therefore, research was conducted on the performance of existing drainage channels in the Pangkajene Islands State Agricultural Polytechnic campus area, so as to maximize the function of the drainage channels.
The purpose of this research is to identify the condition of the drainage channel of the Pangkajene Islands State Agricultural Polytechnic Campus and evaluate the existing Campus drainage network system in accommodating runoff discharge, channel dimensions and flow direction in channels that occur inundation in the Campus Environment.

LITERATUR REVIEW
Drainage comes from the English word "drainage" which means to drain, drain, dispose of or drain water.Drainage can also be defined as a series of water structures that function to reduce and/or remove excess water from an area or land, so that the land can be optimally utilized.Drainage is also defined as an effort to control groundwater quality in relation to salinity (H. Tangkudung, L. et al., 2013).
Channel Classification when viewed in physical terms (hierarchical arrangement of channels) urban drainage systems are classified on primary, secondary, tertiary channels and so on.a.Primary Channels Channels that utilize rivers and creeks.Primary channels are the main channels that receive flow from secondary channels.b.Secondary channels Channels that connect tertiary channels with primary channels (built with concrete / cement plaster).c.Tertiary channels Channels for draining household waste into secondary channels, in the form of stucco, pipes and soil.d.Kwarter Channel Collector channel of the local drainage network.Hydrology is the science related to water on earth, both regarding its occurrence, circulation and distribution, its properties and relationships with its environment, especially with living things.The science of hydrology is strongly influenced by hydrological parameters in an area such as rain intensity, climatological conditions (wind, air temperature, air humidity, and solar irradiation), land conditions (watershed) such as soil type, land use, land slope, and so on.The hydrological analysis used in this planning is using the Modified Rational method.This method can be used because it is in accordance with the existing data and field conditions.This method is used with the assumption that DTA has a wide area (C. Deva, et al., 2021).Factors considered in the calculation of the average maximum regional rainfall are the number of rain gauge posts and watersheds (Andrianto, J. et al., 2021).
Distribution analysis is generally divided into two: Discrete distribution is Poisson method and binomial method, while continuous distribution is Normal method, Log Normal method, Log Pearson method and Gumbel method.This frequency analysis is based on the statistical properties of past event data to obtain the probability of future rainfall amounts.
Flow in open channels and closed channels that have free surfaces is called free surface flow or open channel flow.In closed drainage channels in the form of culverts, there is a possibility of free flow during normal times and during flooding due to sudden rainfall the water will fill the culverts so that the flow is depressed.Channel capacity aims to determine the ability to channel / pass water (discharge).Channel dimensions are determined based on maximum Q, flow velocity, channel slope, and the type of channel material to be used (Muhamad Arifin., 2018).

METHODOLOGY
This research was conducted in July-October 2023 in the Pangkajene Islands State Agricultural Polytechnic Campus Area.
The tools used in this research are Waterpass, Meter, Peg, Unting-unting, GPS, Geographic Information System Application, stationery and documentation tools.The materials used are 4/6 blocks for making stakes.
The research method used is descriptive quantitative, which is a method of calculation and description of the results of field data processing.a. Secondary Data 1) Rainfall data for the last 10 years, obtained from the Department of Resources.2) Topography Map, Drainage Network Map and Situation Map, obtained from Politani Pangkep Campus Planning Section.b.Primary Data 1) Survey of channel base elevation and channel slope The channel base elevation survey aims to determine the slope of the channel so that it can later be used to calculate channel hydraulics.2) Survey of channel length, channel shape and channel material This survey aims to determine the channel manning coefficient for channel hydraulics calculations.

Data Collection Method
Secondary data collection is obtained from related agencies while primary data collection is obtained from direct measurement in the field of the research location using a Waterpass measuring instrument to measure elevation and channel length.

Data Analysis
Analysis of research results using descriptive analysis in the form of tabulations and images.

Data Analysis of Elevation
In this research to calculate the design flood discharge, namely by using rainfall data for 10 years (2013-2022) obtained from the Department of Natural Resources, Cipta Karya and Spatial Planning Prov.South Sulawesi and UPT Je'neberang.The daily rain data for 10 years (2013-2022) obtained is then sought for the maximum value in each year.Maximum daily rainfall data can be seen in table 1.
Table 1.Maximum Daily Rainfall Data of Ralla Station

Determination of Distribution Type
Distribution type analysis is carried out with the aim of determining rainfall estimates with a certain return period using a statistical approach based on past rainfall data can be seen in table 2.

Log Pearson III Distribution Plan Rainfall Analysis
The following results of the frequency distribution calculation for the Log Pearson III distribution can be seen in Table 4.
The following is an example of the calculation of planned rainfall analysis with the Log Pearson III distribution using equation ( 14) For a return period (T) of 2 years.X2 = 10 log2,2095-0,8003+ (-0,8003x0,1320) = 162,0095 mm D Criticalx = 0,409 0 D Ma. < D Critical, then the theoretical distribution used to determine the distribution equation is acceptable.

Surface Runoff Coefficient
The surface runoff coefficient is obtained from the combined average of the area and runoff coefficient of each land use in each sub-drainage basin.To obtain the surface runoff coefficient, it is necessary to first classify the land use in the Sub-DTA in each drainage channel.The drainage channel service scheme and the condition of the water catchment area in the Politani Campus area can be seen in Figure 3, Figure 4, and Figure 5. Based on the calculation of the average multiplication of land use area and Runoff coefficient, the composite coefficient of 0.325 can be seen in Table 8.The calculation of the channel slope is obtained from the drainage length divided by the height difference from the waterpass measurement results.

CONCLUSION
Based on the results of the analysis on the evaluation of the politani pangkep campus drainage network, it can be concluded that: a. Drainage capacity < Flood Discharge Plan for 2 years and 5 years, so there is a need for planning in increasing drainage capacity.b.The results of the calculation and analysis show that the drainage channel needs to be redesigned by increasing the width and height dimensions that can accommodate the 2-year return period design discharge.modification is done by replacing the drainage with precast concrete materials considering the ease of work.

Table 2 .
Calculation of Statistical Approach

Table 4 .
Log Pearson III Distribution Plan Rainfall Analysis

Table 5 .
Log Pearson III Distribution for Coefficient of Skewness

Table 6 .
Log Pearson III Distribution Plan Rainfall AnalysisThe probability distribution test is used to determine whether the selected probability distribution equation can represent the statistical distribution of the data sample being analyzed.In this case, the Smirnov-Kolmogorof Test method is used.The following are the results of the distribution suitability test analysis, can be seen in table 7:Table7.Smirnov-Kolmogorof Test

Table 8 .
Calculation Result of Composite Runoff Coefficient