Corresponding Author:
Muhamad
Qori Fajar
E-mail:
[email protected]
INTRODUCTION
Indonesia is a country that
has many water resources and rivers that play an essential role in people's
lives (Sholi et al., 2020; Yusuf et al., 2022).
Rivers are a source of clean water and serve as transportation routes,
recreational areas, and ecosystems to support biodiversity (Bui et al., 2024; Gu et al., 2025; Ma et al., 2024; Tong
et al., 2024). However, with the development of human settlements and
activities, issues related to river management, such as floods and erosion, are
becoming more frequent. Therefore, effective river management is essential to
reduce these negative impacts (Dehghani Darmian &
Schmalz, 2024; Huang et al., 2024; Li et al., 2024; Vall-Casas et al., 2024).
Cisanggarung River, located
in West Java Province, often overflows during the rainy season, making it
vulnerable to floods. The floods disrupt the surrounding communities' daily
activities and damage infrastructure and property. More river channel capacity
can influence the occurrence of floods as it cannot contain large water flows.
Inadequate river channel capacity to contain incoming water flows can lead to
flooding in the surrounding areas.
Recent studies have highlighted the
growing concerns regarding flood risks in river basins, emphasizing the need
for region-specific research. For instance, research by Dewandaru et al. (2023) examined flood control measures in Jombang
Regency, while Efrizal et al. (2022) explored
drainage effectiveness in Jepara Regency. Expanding upon these works, this
study aims to define the specific research problem of flood overflow in
Cilengkrang Village, emphasizing its significance for local communities.
This research utilizes the HEC-RAS
(Hydrologic Engineering Centers River Analysis System) software, developed by
the Army Corps of Engineers, to model flood behavior in the Cisanggarung River.
HEC-RAS is an open-source tool widely used by civil engineers and hydrology
experts for simulating water flow in open channels (Bharath et al., 2021; Hadi & Almansori, 2023; Phyo et al.,
2023; Zeiger & Hubbart, 2021). This study will identify
high-risk flood areas and provide recommendations for improving river channel
capacity, contributing to better water resource management in the Cisanggarung
River.
This research also
demonstrates how floods overflow around Cilengkrang Village, which is traversed
by the Cisanggarung River, using the HEC-RAS (Hydrologic Engineering Centers
River Analysis System) software. The Army Corps of Engineers developed the
software, which is open-source and useful for flood and river flow modeling. Civil
engineers and hydrology experts use it worldwide to simulate water flow in open
channels like rivers. With HEC-RAS, river flow profiles, channel capacities,
and flood risks can be analyzed. This research will model the flood overflow of
the Cisanggarung River using HEC-RAS. This research aims to identify parts of
the river with a high risk of flood overflow and provide recommendations for
improvements or interventions to increase river channel capacity. It is hoped
that this research can help manage the water resources of the Cisanggarung
River, especially in flood risk mitigation.
METHOD
Research Location
This
study was conducted from August to September 2024 in the Cilengkrang Village
area, through the Cisanggarung River in Cirebon Regency (6°54'55.05" S
108°44'20.00" E). It began by collecting data related to the BBWS (Cimanuk—Cisanggarung).
The
method used is the quantitative method, which is a research approach that uses
numbers and statistics to systematically collect, analyze, and interpret data (Frick, 2015). This research focuses on hydrological
and hydraulic analysis. Hydrological analysis includes rainfall calculation,
average rainfall using the Thiessen polygon method, frequency analysis,
rainfall intensity, Nakayasu, and planned discharge. Hydraulic analysis uses
HEC-RAS software to obtain information about flood levels in the studied area (Estelaji et al., 2024; Kannapiran & Bhaskar, 2024;
Rahman & Ali, 2024). The Nakayasu method, which estimates river flow
hydrographs based on adequate rainfall, involves using hydrograph observations
from various watersheds. Meanwhile, the Thiessen Polygon method divides the
study area into polygons based on the proximity to rainfall measurement
stations. This allows for a more accurate estimation of average rainfall across
the region.
Additionally,
incorporating a flow diagram of the research process would significantly
enhance clarity and transparency. This diagram could visually represent the
steps from data collection and analysis to applying HEC-RAS modeling. Such an
illustration would help readers better understand the methodology and the
interconnections between different stages of the research, ultimately
strengthening the overall presentation of the study.
RESEARCH AND DISCUSSION
Average Rainfall Method of Thiessen
Polygon
The Thiessen Polygon method estimates the average rainfall in a
certain area by dividing the area into several polygons, each representing the
influence of one measurement station. The polygons are formed so that every
point inside is closer to that station than any other station.
Figure 1.
Thiessen Polygon
Area
Table 1. Average Rainfall Method of Thiessen Polygon
Description:
A = Area
(km2)
d = Average
rainfall height of the area
d1,
d2, d3, ... dn = Rainfall height at positions 1, 2, 3,... n
A1,
A2, A3,... An = Area of influence at positions 1, 2, 3, ... n
Frequency Analysis
Table 2. Gumbel
Distribution
Description
:
XT
= Planned rainfall with a period of T years
Xr
= Maximum average rainfall
K
= Frequency factor
Sx
= Standard deviation
Rainfall Intensity Mononobe Method
Table 3. Rainfall Intensity for a Few
Hours
The formula used is:
I=T/t^n
Where:
I = Rainfall intensity (mm/hour)
R = Total rainfall during a specific period
(mm)
t = Duration of the rainfall (hours)
n = Exponent factor, usually 0.6 to 0.8,
depending on the local geographical and climatological conditions. Generally,
the value of n used in the Mononobe method is 2/3 (0.67).
The Rainfall Intensity Mononobe Method is
widely used for estimating rainfall intensity over a specific duration. This
empirical method is particularly effective in hydrological studies, where
understanding the relationship between rainfall duration and intensity is
crucial for flood modeling and water resource management. The method technique is
a formula that calculates rainfall intensity (I) based on total rainfall (R)
and the duration of rainfall (t) (Bashori
& Purwono, 2024; Cyr, 2016; Fajri et al., 2023).
Nakayasu
The Nakayasu method was
developed based on observations of natural unit hydrographs originating from many
watersheds in Japan. This is one of the synthetic unit hydrograph methods used
in hydrology to estimate river flow hydrographs based on adequate rainfall in
the river basin area (Febrianto et al., 2023; Rovita
Yuniarti, 2022).
Table 4. Synthetic Unit
Hydrograph Analysis Parameters Using the Nakayasu Method
Figure 1.
Nakayasu Area
Chart 1.
HSS DAS Nakayasu
The HSS Nakayasu formula is as follows:
(2.35)
(2.36)
(2.37)
(2.38)
for t < Tp
for
Tp < t < Tp + T0,3
(2.41)
for Tp + T0,3 + 1,5T0,3
(2.42)
for t > Tp
(2.43)
Debit Plan
Based on the results of the
hydrological analysis using the frequency distribution method, the planned
discharge value is 2137.411 m³/second. This discharge is calculated for a specific
return period that reflects the potential for flooding within a certain period
in the study area. This discharge value indicates the magnitude of water flow
that needs to be anticipated in flood control infrastructure planning (Efrizal
et al., 2022; Rizani et al., 2023; Rovita Yuniarti, 2022; Sholi et al., 2020).
Table 5. Flood Discharge Analysis
for a 25-Year Return Period
Chart 2.
Planned Unit Hydrograph
Discharge (HSS)
HEC-RAS 6.5 Modeling Results
Chart 3.
Flood distribution in HEC-RAS modeling
Figure 3.
Flood
simulation modeling with HEC-RAS 2D
Figure 4.
Flood
simulation modeling with HEC-RAS 2D
Chart 4.
Water Surface Elevation on “A”
Chart 5.
Water Surface Elevation on “1A”
Chart 6.
Water Surface Elevation on “1B”
Chart 7.
Water Surface Elevation on “1C”
Chart 8.
Water Surface Elevation on “1D”
Chart 9.
Water Surface Elevation on “1E”
CONCLUSION
This study has effectively highlighted
the significant variability in annual rainfall in the Cilengkrang Village area,
with the highest recorded rainfall reaching 1290 mm in 2020. The calculated,
planned discharge of 2137 m³/second for the Cisanggarung River underscores the
urgent need for adequate flood disaster mitigation measures. HEC-RAS modeling
indicates that the river's cross-section capacity cannot accommodate flood
discharge, particularly in areas near settlements.
Several recommendations have been
proposed to enhance flood mitigation in Cilengkrang Village, including
increasing the river's cross-section through widening or excavation,
constructing flood walls, and developing flood control infrastructure such as
small dams or embankments. Additionally, implementing an early warning system
will enable residents to take preventive actions ahead of potential floods.
Reflecting on future research
possibilities, exploring advanced modeling techniques and long-term monitoring
of flood patterns would be beneficial, which could further improve flood risk
assessments in the region. Emphasizing the practical implications of these
recommendations is crucial; implementing such measures can lead to improved
community safety, reduced property damage, and better management of water
resources. Overall, this research provides valuable insights into flood
dynamics and offers actionable strategies to mitigate flood risks, thereby
enhancing resilience in Cilengkrang Village and its surroundings.
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