Flood Routing and Dam Breach Parameter Calculation on Sepaku Semoi Dam

This study endeavors to develop a comprehensive flood routing model and ascertain dam breach parameters at the Sepaku Semoi Dam. Driven by the escalating threat of floods due to climate change and urban expansion, effective water management strategies are imperative. The increasing demand for water, juxtaposed with limited supply, underscores the pivotal role of dams in maintaining water resources, despite the inherent risks they pose in the event of failure, including loss of life, property damage, and environmental degradation. Fo-cused on the potential causes of dam collapse, particularly overtopping and piping, this research investigates whether the Sepaku Semoi Dam has experienced overtopping through flood routing analysis, complemented by the calculation of breach parameters using the Zhong Xing HY21 model. The primary aim is to enhance understanding of flood dynamics around the dam and bolster the reliability of flood hazard predictions. Through Gap analysis, the study underscores the urgent need for improved flood risk management and understanding of dam failure potential. Employing a methodology that integrates hydrological and hydrodynamic modeling, the study aims to provide deeper insights into flood patterns around the dam and facilitate more precise calculations of dam breach parameters. The implications of this research extend to enhanced flood risk mitigation, emergency planning, and increased dam infrastructure reliability. The study’s unique approach lies in its holistic integration of flood modeling and dam breach parameter calculation, which aligns with practical disaster risk management needs. Flood routing analysis indicates that the Sepaku Semoi Dam has not experienced overtopping, as evidenced by the remaining guard heights exceeding the standard guard height, while breach parameters reveal critical insights into potential dam failure scenarios. This is an open access article under the CC BY 4.0 license.


INTRODUCTION
Currently, the demand for water is increasing in every region.However, water availability is severely limited, necessitating the utilization of water resources.One effort in maintaining water resources is the health-Journal homepage: https://att.aptisi.or.id/index.php/att

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❒ 137 Preneur construction of water utilization facilities, namely dams.Dams are structures made of earth, rock, or concrete designed to store water while also serving as barriers and reservoirs for mine waste or mud (Ministry of Public Works Regulation No. 27/PRT/M/2015, 2015).Nevertheless, dams also entail the risk of flash floods, which can result in loss of life, property damage, and environmental devastation if they collapse [1], such as the catastrophic collapse of the Gintung Dam, which claimed hundreds of thousands of lives [2].
The Sepaku Semoi Dam is located in Sepaku District, North Penajam Paser Regency, East Kalimantan.The dam serves as a flood reducer and raw water supply for the Industrial Estate (IKN) at a rate of 2000 liters/second and for Balikpapan at a rate of 500 liters/second.Therefore, this analysis is conducted to determine whether the dam will experience collapse due to overtopping or not.Additionally, this analysis aims to prepare fracture parameters for use in simulating dam collapse with the Zhong Xing HY21 model [3].

LITERATURE REVIEW
Dam collapse can occur due to overtopping or piping.Dam collapse can lead to flash floods that can claim lives, cause property loss, and environmental damage.Dam collapse begins with the occurrence of cracks.Cracks are divided into 2 types:

Cracks Due to Overtopping
Cracks due to overtopping occur when the dam cannot contain excess water, causing erosion downstream of the dam body.Cracks due to overtopping are simulated in the form of triangular, square, or trapezoidal cracks.These cracks gradually widen from the top of the dam downwards until reaching the foundation.The flow passing through the cracks is calculated as flow passing over the weir width.In the dam collapse model, cracks are assumed to develop over a certain time interval and have a final shape depending on the final base width parameter (b) and other parameters (Z) [4].the dam or foundation.Piping can also be called a leak in the body/foundation of a dam due to reed erosion.Collapse due to piping is simulated by determining the elevation of the piping axis which is considered a rectangular hole.Generally, but not yet certain, the fracture base elevation (hbm) that will be reached after it gradually widens to a width (b) which previously started at the elevation of the fracture starting point (hf), namely the base elevation of the dam [5].Meanwhile, the parameter value (Z) of the piping is 0 because it is square, so it has no slope [6].Dam collapse, also called dam collapse, according to PUPR Ministerial Regulation No. 27/PRT/M/2015 is defined as follows: partial or complete collapse of the dam or its additional structures; damage that causes the dam to not function; or a combination of both factors.Dams can break for a variety of reasons, and there are many potential causes.Fractures, namely holes that form in the dam body when it collapses, occur before the dam completely collapses [7].This happened before the dam actually collapsed [8].Understanding of failure mechanisms is still lacking, regardless of whether the dam in question is a concrete dam or an earthfill dam.The following is a reference for selecting fracture parameter values and the total time required for dam demolition for various types of dams.Performance is the result in terms of quality and quantity achieved by an employee in carrying out his duties in accordance with the responsibilities given to him [9].Performance is about behavior or what employees do, not about what employees produce or the results of their work [10].Performance is seen as the implementation of one's actions or abilities.Good performance is also related to the achievement of quality, quantity, cooperation, reliability, and creativity.Employee performance is considered as a measure of the quality of human resources owned by the organization [11].
Fractures formed in earthfill dams tend to have an average width (Bbar) in the range (had Bbar 3hd) where hd is the height of the dam.This Bbar range value is proven by a summary report [12].Therefore, the fracture width for an earthfill dam is usually much smaller than the total length of the dam measured across the valley [13].Piping failure occurs when initial gap formation occurs at several points in the dam body caused by erosion of the dam body which causes water leakage from the dam [14].This is because the upstream surface is slowly eroded in the early stages of piping [15].As erosion progresses, the cracks that occur become larger so that the upper part of the dam body collapses (BOSS DAMBRK Hydrodynamic Flood Routing User's Manual) [16].In calculating dam failure parameters, the average failure width and failure time are sought [17].

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T IM E BF = 0, 8((V r/hd2)0, 5) Where The Manning roughness coefficient is a figure of roughness and resistance found in the basic conditions of the channel [18] [19], where this figure is able to inhibit the speed of water flow in the channel and reduce the value of the speed and flow rate.The Manning coefficient (n) for each cross section along the river downstream of the dam where the flood will pass is as follows:

RESEARCH METHOD
The proposed research method for analyzing flood flows and calculating dam opening parameters at Sepaku Semoi Dam involves a multidisciplinary approach [20].First, a field survey will be carried out to collect topographic data and hydrological characteristics of the river basin associated with the Sepaku Semoi Dam [21].This data will be used as a basis for building an accurate hydrological model.Next, we will apply state-of-the-art hydrological techniques, such as the HEC-RAS model, to simulate flood flows that may result from dam failure [22] [23].
The second step involves a sensitivity analysis of the parameters that influence changes in dam conditions and the potential probability of dam rupture [24].We will take into account various potential scenarios that affect dam strength and the hydrological characteristics of river flow, such as sudden changes in river discharge due to heavy rains or changes in topography due to natural disasters [25].This analysis will help identify the most critical conditions that can cause dam failure [1].
The final step is model validation and verification.We will compare the simulation results with previously collected field data, including historical data on flood flows and dam conditions [26].This validation will ensure the accuracy of the model and the reliability of the predictions produced, thereby providing a strong foundation for disaster mitigation planning and flood risk management around the Sepaku Semoi Dam [27].
This research was conducted on the Sepaku Semoi Dam which is located in North Penajam Paser Regency, East Kalimantan, at coordinates 101°13'12" East Longitude and 6°45'41" North.The territorial boundaries are as follows: The Mediapreneur data needed to carry out flood investigations is the design flood discharge data for the Sepaku Semoi Dam and the curved capacity of the Sepaku Semoi Dam reservoir [28].Data obtained from the Kalimantan River Region IV Center.The design flood discharge for the Sepaku Semoi Dam can be seen in Table 3. Flood tracing is carried out to calculate the maximum water level of the reservoir [29].This is done to determine the most cost-effective (optimal) height of the dam but remains safe from the risk of flooding.The basic formula chosen is: with : I = Reservoir inflow (m 3 /sec) O = Reservoir outflow (m 3 /sec) ds dt = Water discharge held in a reservoir for a short period of time So, the equation can be written as: This equation can be changed to the following: With : S 1 = Reservoir storage at the start of the tracking period (measured from the top of the spillway structure/tunnel axis) Q 2 = The debit that occurs at the start of the tracking period

Flow on the Spillway
A spillway is a building used to overflow water that cannot be accommodated by a dam.To determine the dimensions of the spillway, it is adjusted to the 1000 year return period discharge (Q1000) and must be able to pass the maximum flood discharge (QPMF) without experiencing overtopping [30].Calculation of discharge through the spillway uses the following formula:  Based on flood investigations that have been carried out, the Sepaku Semoi Dam does not experience overtopping so the parameter calculations carried out are only for the piping scenario [36].The piping scenario parameters used include top, middle and bottom piping.This parameter is used in the Zhong Xing HY21 program input [37].The following is an explanation of the input for the Padan dam collapse simulation for the Sepaku Semoi Dam:

Figure 1 .
Figure 1.Illustration of Cracks Due to Overtopping

❒Figure 5 .
Figure 5. Inflow Outflow Relationship Graph on the Spillway

Figure 6 .
Figure 6.QPMF Inflow Outflow Relationship Graph on the Spillway

Table 1 .
Summary of Dam Collapse Parameter Equations

Table 3 .
Flood Discharge Design for the Sepaku Semoi Dam

Table 4 .
Curved Capacity of the Sepaku Semoi Dam Reservoir