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Flood Mapping Potential Areas Using HEC-RAS Software (Case Study: Kota
Lama of Semarang)

Article in IOP Conference Series Earth and Environmental Science · April 2024
DOI: 10.1088/1755-1315/1324/1/012100

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Flood Mapping Potential Areas Using HEC-RAS Software
(Case Study: Kota Lama of Semarang)

Christian Cahyono and Loviandy Rusli

Civil Engineering Department, Faculty of Engineering, Bina Nusantara University,
Jakarta, Indonesia 11480
Abstract. Semarang has experienced floods every year, with a peak in the rainy season. At the
end of 2022, there was heavy rain which caused the East Flood Canal River to overflow. As a
result, the floods inundated several areas in Semarang City, including Kota Lama of Semarang.
This study aims to determine the value of the designed discharge, the area of the flood
inundation that occurred and the flood inundation map for return periods of 2, 5, 10, 25, 50 and
100 years. The methodology of this research consist of hydrological analysis, hydrological
modelling with HEC-HMS and hydraulics modelling with HEC-RAS and integration with
ArcGIS. In this study, it was found that for a return period of 2 years the planned flood
discharge value was 153.7 m3/second with an inundation area of 406 Ha and a flood height of
17 cm to 68 cm, up to a return period of 100 years with a planned flood discharge value of
455.7 m3/second with an inundation area of 796 Ha and a flood height of 83 cm to 180 cm.

Keywords: Flood, HEC-HMS, HEC-RAS, Kota Lama of Semarang

1. Introduction
Semarang East Flood Canal River is one of the flood control river systems in Semarang City, which is
located in the eastern part of Semarang City. Created in 1889 during the Dutch colonial period to
overcome the floods that occurred at that time. Flooding is a condition where water runoff has a height
above the normal water level, causing stagnant water on a lower surface on the river side. Some of the
factors that cause flooding are sea tides and high-intensity rainfall.
At end of December 2022, rain with high intensity caused several areas in Semarang City to be
flooded. The recorded rainfall on December 31, 2022 was 92.7 mm. Every year, Semarang has
experienced several flood disasters due to high rainfall. This can be proven by the 10-year rainfall data
that occurs with an average rainfall intensity including very heavy rain (100 – 150 mm/day).
In this study an analysis of flood inundation mapping will be carried out in Semarang Regency which
focuses on the Kota Lama of Semarang. Flood inundation mapping analysis will be carried out with
the ArcGIS program to display geographical conditions, HEC-HMS for hydrological analysis and
modeling and HEC-RAS for hydraulics modeling for two-dimensional river flows.
2. Study Literature
2.1 Hydrological Cycle
The hydrologic cycle or water cycle is a process in which water originating from the earth's
atmosphere will continuously return to the atmosphere and occur repeatedly with the aim of
maintaining the availability and amount of water on earth to remain stable. The stages of the
hydrologic cycle are evaporation, transpiration, evapotranspiration, sublimation, condensation,
advection, precipitation, runoff, infiltration, and conduction [1].
2.2 Rivers and Watersheds
A river is a container or channel where water flows from upstream to downstream and is bounded by a
boundary line on the right and left. In general, the water in the river flow comes from springs, dew,
rain, and snow. The flow of water moves from a high place to a lower place due to the force of gravity.
Some of the functions of the river are agricultural irrigation, tourism objects and water reserves.
A watershed is a water system area that is scientifically formed and bounded by hills and
mountains which receives, collects, and distributes rainwater that falls into a watershed through a river
system in the area and is discharged at one outlet point. [2].
2.3 Flood
Flooding is a condition where water runoff has a height above the normal water level, causing puddles
of water on a lower surface on the river side [3].
2.4 Designed Flood
Designed flood is the maximum flood discharge that is expected to occur during a predetermined
return period. The value of the planned flood discharge is determined according to an analysis of the
frequency of rainfall during a predetermined return period [4].
2.5 Hydrological Analysis
2.5.1 Data Testing
Outlier test is performed to determine the existence of data with significant differences in value among
other data. The Grubbs & Beck method sets the upper limit (XH) and lower limit (XL) where the test
is accepted if there is no data that exceeds the upper outliers and is smaller than the lower outliers [5].
2.5.2 Frequency Distribution
The frequency distribution is a calculation analysis to obtain the probability of the occurrence of a
hydrological event. For hydrological analysis, at least 2 years of hourly rainfall data or at least 10
years of annual rainfall data is required [5].
2.5.3 Chi-square test
The chi-square test is a test of the fit of the distribution function based on the weight of the sum of the
squares of the difference between the observations and the theory which is divided into several sub-
groups [5].
2.5.4 Smirnov Kolmogorov test
The Smirnov Kolmogorov test is a distribution function compatibility test based on the maximum
vertical distance between the observations and the theoretical sample distribution [5].
2.5.5 Rain Distribution
The distribution of rain is the pattern of rain in a certain area with various distributions of hourly
percentage values. Calculation of hourly plan rain distribution is recommended to be carried out in
accordance with the “Technical Guidelines for Dam Design Flood Calculations”. Design rainfall
distribution is calculated using PSA-007 cumulative rainfall distribution [5].
2.6 ArcGIS
ArcGIS is a geographic information system (GIS) processing tool that displays and processes data
from actual geographic conditions and functions to display and process relevant geographic
information systems and create or edit maps [6][7].

2.7 HEC-HMS
HEC-HMS (Hydrologic Engineering Centre - Hydrologic Modelling) is a program from the US Army
Corps of Engineers designed to operate the simulation of hydrological processes and routing processes
in river areas [8].
The parameter needed in calculating effective rainfall is the curve number (CN) value. The CN
value describes the characteristics of a watershed such as land use, soil type, humidity, and vegetation
conditions. The CN value will affect the amount of rainfall lost in the form of infiltration [9].

2.8 HEC-RAS
HEC-RAS (Hydrologic Engineering Centre - River Analysis System) is a program of the US Army
Corps of Engineers designed to perform river flow modelling in one and two dimensions, sediment
analysis, water quality analysis and hydraulics building functions [10][11][12][13].

3. Result and Discussion

3.1 Watershed Modelling with Arc-GIS

Figure 1. Watershed

Based on the watershed modelling that has been done with ArcGIS which is shown in Figure 1, it is
found that the area of the watershed is 4984 ha, the slope value is 0.2% and the length of the river path
is 13.32 km.
3.2 Validation
Table 1. Distribution of Rain PSA-007 Rain 6 Hours Validation
Time (Hour) Distribution R (mm)
1 5% 4.64
2 10% 9.27
3 60% 55.62
4 16% 14.83
5 6% 5.56
6 3% 2.78
Total 100% 92.70

Table 1 is the value of the 6-hour rain distribution for validation calculations. The rainfall used is the
daily rainfall value on December 31, 2022, taken from the Ahmad Yani meteorological station.

Figure 2. 6 Hours Validation Flood Hydrograph

From Figure 2, it can be seen the flood hydrograph of flood event of December 31, 2022. By using this
hydrograph we model and verified the both hydrological and hydraulics model of study location.

Figure 3. Inundation Flood Distribution Rain Validation

 Figure 4. Validation Inundation Flood

In this study, the validation of inundation height calculations cannot be carried out by direct surveys in
the field, so what can be done is to carry out hydrological and hydraulics modelling using rainfall data
that occurred on December 31, 2022. The news attachment shows flooding around Kota Lama
Semarang ranging from between 15 cm to 90 cm which can be seen from Figure 3 and 4. Based on the
results of the hydrological and hydraulics modelling that has been done, the inundation height around
the Kota Lama of Semarang is 54 cm so that it can be stated that the calculation and modelling of
flooding in the Kota Lama Semarang can be validated because it is in accordance with the incident
news.

3.3 Hydrological Analysis

Table 2. Distribution Terms Test Results
Rainfall (mm)
Return Log Pearson
Normal Log Normal Pearson III Gumbel
Period III
Method Method Method Method
Method
2 109.25 102.93 106.72 104.27 102.90
5 142.18 140.54 141.19 140.98 137.43
10 159.40 165.41 160.72 163.90 160.30
25 177.76 196.78 182.70 191.44 189.19
50 189.62 220.13 197.56 211.04 210.62
100 200.28 243.48 211.37 229.94 231.89
Smirnov-Kolmogorov Test
Dmax 0.04 0.04 0.04 0.05 0.06
DCr 0.41 0.41 0.41 0.41 0.41
Dmax
< Accepted Accepted Accepted Accepted Accepted
DCr
Chi-Square Test
X2 3 3 5 5 2
X2Cr 5.991 5.991 5.991 5.991 5.991
X2 <
Accepted Accepted Accepted Accepted Accepted
X2Cr
Terms of each distribution
Cs 0.00 0.47 0.17 0.37 0.45
Ck -0.67 -0.28 -0.62 -0.44 -0.30
Cv 0.30 3.26 0.30 0.30 0.29
- - - Accepted -
 Table 3. Distribution of Rain PSA-007 Rain 6 hours
Distribution of Rain PSA-007 Rain 6 hours (mm)
Return Period 2 5 10 25 50 100
Rainfall 104.27 140.98 163.90 191.44 211.04 229.94
Time (hour) Distribution R (mm)
1 5% 5.21 7.05 8.20 9.57 10.55 11.50
2 10% 10.43 14.10 16.39 19.14 21.10 22.99
3 60% 62.56 84.59 98.34 114.87 126.63 137.96
4 16% 16.68 22.56 26.22 30.63 33.77 36.79
5 6% 6.26 8.46 9.83 11.49 12.66 13.80
6 3% 3.13 4.23 4.92 5.74 6.33 6.90
Total 100% 104.27 140.98 163.90 191.44 211.04 229.94

Table 2 is the result of the calculation of the frequency distribution which has been tested for chi-
square and Smirnov Kolmogorov and the terms of each distribution. Based on these calculations, the
rainfall plan used is the rainfall from the Log Pearson III method.
Table 3 is the value of the 6-hour rain distribution for return periods of 2, 5, 10, 25, 50 and 100
years. The rainfall used is the result of table 1 calculations.

3.4 HEC-HMS

Figure 5. Hydrological Model

Figure 5 is the basin model used in the hydrological modelling in this research. The data used is the
value of the 6-hour rain distribution which has been calculated in table 3. From this hydrological
modelling, the results of the planned flood discharge for each return period are obtained which shown
in Figure 6 to 11.
 Figure 6. 2 Year Flood Hydrograph Figure 7. 5 Year Flood Hydrograph

Figure 8. 10 Year Flood Hydrograph Figure 9. 25 Year Flood Hydrograph

Figure 10. 50 Year Flood Hydrograph Figure 11. 100 Year Flood Hydrograph

3.5 HEC-RAS

Figure 12. Hydraulic Model

Figure 10 shows the basin model used in the hydraulics modelling in this study. The data used is the
value of the planned flood discharge every hour of the 6-hour rain distribution in each return period.
From this hydraulics modelling, the results of flood mapping and flood depth around the study area
were obtained.

3.6 Flood Inundation Map

Figure 13. Flood Inundation Map

Figure 4 shows a flood inundation map resulting from the integration of hydraulic modelling in HEC-
RAS and ArcGIS. The flood inundation map in Figure 4 is an inundation map with a scale of 1:40,000
which includes mapping of inundation for return periods of 2, 5, 10, 25, 50 and 100 years. It is shown
in the map that in all return period Kota Lama Semarang and Railway Station prone to flooding event
so it is necessary to solve this flooding problems because of the area is important for intercity
transportation.

4. Conclusion
From the results of hydrological modelling using the HEC-HMS with the SCS hydrograph method,
the design flood value for each period is:
2 years = 153.7 m3/second; 5 years = 238.8 m3/second; 10 years = 293.7 m3/second; 25 years =
360.7 m3/second; 50 years = 409 m3/second; 100 years = 455.7 m3/second.
From the results of hydraulic modelling using HEC-RAS, the inundation area and flood height for
each period are as follows:
2 years = 406 Ha, with a flood height of 17 cm – 68 cm; 5 years = 554 Ha, with a flood height of 19
cm – 120 cm; 10 years = 650 Ha, with a flood height of 40 cm – 140 cm; 25 years = 725 Ha, with
a flood height of 60 cm – 160 cm; 50 years = 771 Ha, with a flood height of 72 cm – 173 cm; 100
years = 796 Ha, with a flood height of 83 cm – 180 cm;

5. Suggestion
1. The use of rainfall data obtained through the BMKG website needs to be calculated with data at
other nearby meteorological stations to obtain more accurate results;
2. The determination of the perimeter in hydraulics modelling in the HEC-RAS program should be
enlarged so that it can cover a more actual inundation area.

References
[1] Yang, D., Yang, Y., & Xia, J. (2021). Hydrological cycle and water resources in a changing
world: A review. Geography and Sustainability Volume 2, 115 - 118.
[2] Sukristiyanti, S., Maria, R., & Lestiana, H. (2018). Watershed-based Morphometric Analysis: A
Review. IOP Conference Series: Earth and Environmental Science, 1.
[3] Setiawan, H., Jalil, M., Enggi, M., Purwadi, F., & Christopel. (2020). Analisis Penyebab Banjir
di Kota Samarinda. Jurnal Geografi Gea, Volume 20, Nomor 1, 39 - 40.
https://doi.org/10.17509/gea.v20i1.22021
[4] Thaufiq. (2020). Hydrological Analysis of Movable Weir Planning for Tidal Flood Handling in
Cilacap, Central Java. 4th International Conference on Civil Engineering Research, 2 - 3.
https://doi.org/10.1088/1757-899X/930/1/012078
[5] SNI-2415-2016. (2016). Tata Cara Perhtiungan Debit Banjir Rencana. Jakarta: BSN.
[6] Wigati, R., Lestari, M. D., & Arifin, F. S. (2020). Integrasi HEC-RAS dan GIS dalam
floodplain mapping Sungai Cilemer HM 53+00 – HM 105+00. Teknika: Jurnal Sains Dan
Teknologi Vol 16 No 02, 171 - 178. http://dx.doi.org/10.36055/tjst.v16i2.9134
[7] Muhammad Anshari Matondang, Ahmad Perwira Mulia, Muhammad Faisal. (2022). Analisa
Area Genangan Banjir Sungai Babura Berbasis HEC-RAS dan GIS. Jurnal Syntax
Admiration Vol 3, 180 - 200. https://doi.org/10.46799/jsa.v3i1.381
[8] Zafira Nur Pratiwi, Purnama Budi Santosa. (2021). Pemodelan dan Visualisasi Genangan Banjir
untuk Mitigasi Bencana di Kali Kasin, Kelurahan Bareng, Kota Malang. Journal of
Geospatial Information Science and Engineering, 56 - 64.
https://doi.org/10.22146/jgise.56525
[9] Ramadan, A. N., Nurmayadi, D., Sadili, A., Solihin, R. R., & Sumardi, Z. (2020). Studi
Penentuan Nilai Curve Number DAS Pataruman berdasarkan Satuan Peta Tanah Indonesia.
Media Komunikasi Teknik Sipil, 259. https://doi.org/10.14710/mkts.v26i2.26563
[10] Setiawan, H. M., Junedi, H., & Zuhdi, M. (2022). Analisis Dan Simulasi Banjir Das Kenali
Kecil Dengan Menggunakan Sig Dan Model Hidraulika Hec-Ras. Program Studi Magister
Ilmu Lingkungan Universitas jambi, 14 - 21. https://doi.org/10.22437/jpb.v5i1.18624
[11] Zevri, A. (2019). Studi Pemetaan Daerah Genangan Banjir Das Sei Sikambing Dengan Sistem
 Informasi Geografis. Teras Jurnal, Vol 9, No 2, 165 - 177.
http://dx.doi.org/10.29103/tj.v9i2.233
[12] Rauf, I., Imran, & Sahdar, I. (2021). Analisis Spasial Tingkat Bahaya Banjir Desa Amasing Kali
Dengan Hec-RAS 2D. Jurnal Teknik Vol. 16, 107 - 119.
[13] Amin, M. A., Ulfah, L., Haki, H., & Sarino. (2018). Simulasi Karakteristik Genangan Banjir
Menggunakan Hec-Ras 5 (Studi Kasus Subsistem Sekanak di Kota Palembang). Jurnal
Penelitian dan Kajian Bidang Teknik Sipil Vol 7, 13 - 24.
https://doi.org/10.35139/cantilever.v7i2.67

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