Tidal Analysis for Planning the Tidal Flood Management and the

Moveable Weir, Case Study in Parit River, Kawunganten Cilacap

Nazariano Rahman Wahyudi

, Henny Pratiwi Adi

, Slamet Imam Wahyudi

and Suntoyo

Department of Ocean Engineering, Institut Teknologi Sepuluh Nopember, Surabaya, Indonesia

Department of Civil Engineering, Universitas Islam Sultan Agung, Semarang, Indonesia

Keywords: Tidal Flood, Water Sea Level, Observation, Analysis.

Abstract: The seawater level always rises globally. Sea level rise has an impact on human life. One of the effects of

rising sea levels is the tidal flood which is one of the adverse natural phenomena. Kawunganten District,

Cilacap Regency is one of the areas affected by the tidal flood. The construction of the moveable dam is a

solution to prevent damage to the region due to tidal flooding. In carrying out dam design planning required

accurate tidal data. This study aims to obtain data and analysis of tides along the river to the river mouth. In

determining tidal data, observations are made using an automatic survey tool called DIVER. The tidal analysis

is done by applying the least square method to obtain the tidal harmonic constant at the study site. Base on

observation data for 75 days, the results of tidal data analysis as a reference for planning flood management

and moveable. The analysis gives the value of MSL (Mean Sea Level) of 0,996 m, MHWS (Mean High Water

Spring) of 1,7 m, MLWS (Mean Low Water Spring) of 0,292 m, HHWS (Highest High Water Spring) of

1,992 m and LLWS (Lowest Low Water Spring) of 0,00 m as elevation reference for the infrastructure

development.

1 INTRODUCTION

Indonesia has diverse water characteristics. The

diversity of waters in Indonesia is due to Indonesia's

geographical condition which consists of various

kinds of islands. Flood disaster is one of the disasters

that often hit the Indonesian archipelago which has

low land elevation. One type of flood that can provide

many losses in various aspects is tidal flooding. The

parameter that is very influential on the occurrence of

seawater is sea level rise (Yudi R. K. et al., 2017).

Cilacap is one of the districts in Indonesia that is

vulnerable to the occurrence of tidal flood. This is

because the Cilacap area is a lowland area with very

slow soil infiltration capability (Yani and Sumunar,

2019). Cilacap Regency is located in Central Java

Province. Geographically, Cilacap Regency is on the

southern side of Java, which faces the continuation of

the Indian Ocean. The Cilacap district area that was

harmed due to the tidal flood was Ujungmanik

Village, Kawunganten District. This area has a

distance of 16,662 m from the mouth of the Cilacap

river. The tidal flood that occurred in this region came

from the overflow of the Parit river along the

Kawunganten district. Tidal floods reduce social and

economic activities of the people in Kawunganten

sub-district. One of the disturbed community

activities is farming due to tidal floods that have risen

to the ground causing sea water to damage crops in

agricultural and plantation areas. In addition, the

access road used by the community to carry out their

activities was also affected due to sea level rise

reaching the road surface. Housing, places of worship

and schools were also affected by tidal flood that

came from the overflowing moat river. Flood

disasters always have widespread impacts on the

destruction of infrastructure, the environment,

ecosystems and human life (Salami et al.,2017). High

levels of community resilience to flood disasters are

represented at low levels of flood risk (Isa et al.,

2018).

Floods have given various kinds of adverse effects

to the community and therefore preventive measures

are needed to reduce these impacts (Subiyakto et al.,

2019).To overcome the problem of tidal floods, there

are several solutions implemented. The application is

done by structural and non-structural methods

(Wahyudi N. R. et al., 2019). In solving the problem

of tidal flooding that occurred in Kawunganten

Village, it is necessary to apply the structural method.

Wahyudi, N., Adi, H., Wahyudi, S. and Suntoyo, .

Tidal Analysis for Planning the Tidal Flood Management and the Moveable Weir, Case Study in Parit River, Kawunganten Cilacap.

DOI: 10.5220/0010287702810286

In Proceedings of the 7th International Seminar on Ocean and Coastal Engineering, Environmental and Natural Disaster Management (ISOCEEN 2019), pages 281-286

ISBN: 978-989-758-516-6

281

The structure needed is a polder system and a door

that will be a solution to solving this problem. The

polder system is effective in reducing the rise in water

level due to tidal flooding and can reduce the risk

caused by tides. Polder system is a technology in

water control that is often applied in various cities

with tidal flood problems. To optimize the

performance of a polder system, it is necessary to

have a good channel for the flow of water (Wahyudi

et al., 2019). In the construction of polder systems,

several infrastructures are needed which include

retention ponds, drainage systems, water pumps, and

dams/floodgates (Nugroho et al., 2016). To develop

infrastructure to handle tidal floods it needs to be

done in cooperation with the management and

mitigation of tidal floods (Adi and Wahyudi, 2018).

In addition to building various types of

infrastructure, parameters are also needed in planning

infrastructure development, so that it can produce

optimal and efficient results (Hunter J. R. et al.,

2017). By considering tidal parameters, it can

determine the number of costs incurred for the

construction of the weir and as a reference for the

amount of weir needed to overcome tidal floods (Hall

et al., 2019). A very important parameter in polder

system planning is tidal. Estimated water levels

within the tidal range are a suitable tool for

environmental management and risk management for

tidal flood disasters (Sadeghian et al., 2016). Tides

have the most dominant influence on the occurrence

of tidal floods in Cilacap. A tide that comes from

downstream across the river to the upstream

direction. The increase in high seawater is increasing

over time due to the influence of global warming that

occurs.

This study aims to obtain primary data in the form

of tidal conditions along the Parit river and Cilacap

waters. The data that has been obtained is analysed to

determine the type of tides. Tidal data is calculated

and analysed to find important heights needed.

Important elevation obtained is adjusted to the weir

planning for handling tidal flooding and as a

consideration in determining the structure of the weir.

2 METHOD

2.1 Water Level Measurement

Data is collected by using the DIVER survey tool.

This tool is equipped with a pressure sensor, so the

measurement of water elevation also takes into

account air pressure. DIVER is a survey tool applying

the principle of measuring water pressure at the

location under study (Eijkelkamp, 2016). To calculate

the water level, the pressure data are calculated using

the following formula:

𝑊𝐶 = 9806.65

𝑃



+𝑃



𝜌.𝑔

(1)

Where WC = Water Column, P = pressure in

cmH

O, g = the acceleration due to gravity (9,81

m/s

). The water level can be calculated by the

following equation:

𝑊𝐿 = 𝑇𝑂𝐶 −𝐶𝐿 +𝑊𝐶

(2)

Where WL = water level, TOC = pipe depth, CL

= diver depth

Figure 1: DIVER installation scheme.

2.2 Calculation of Tidal Harmonic

Constants

Tidal data is processed using worldtide with the

MATLAB programming language (Boon, 2007). In

the tidal analysis, the least square method is used. The

least-square method is a method for tidal calculations

with the principle of minimizing the tidal elevation

equation so that a simultaneous equation is obtained.

The simultaneous equation is solved using a

numerical method to produce harmonic constants

(Dalpan and Pratomo, 2015). The least square method

is one of the most widely used approaches and

continues to be used in the tidal analysis (Foreman et

al., 2009). The equation used in the least square

method is:

ℎ

()

=ℎ



+

𝑓



𝐻



cos𝜛



𝑡+𝑢



−𝑘









(3)

Where t = time (in hours), ℎ

()

= predicted water

level, ℎ



= average water level, 𝑓



= nodal correction

ISOCEEN 2019 - The 7th International Seminar on Ocean and Coastal Engineering, Environmental and Natural Disaster Management

282

factor for amplitude, 𝐻



= average amplitude in the

nodal cycle (18,6 years), 𝜛



= angular velocity of the

tidal component to j, 𝑢



= odal correction factor for

the phase, 𝑘



= phase lag between the equilibrium tide

at the observation site and the equilibrium tide at

Greenwich at 00.00, 𝑚 = the number of tidal

harmonics to be analysed (Williams, 2013).

Harmonic components that have been calculated

are used as parameters in the calculation of important

tidal elevations. The elevation is useful in analysing

dam planning for the location under study because the

water level is always changing at any time

(Joesidawati et al., 2017). The calculated elevations

are MSL (Mean Sea Level), MHWS (Mean High

Water Spring), MLWS (Mean Low Water Spring),

HHWS (Highest High Water Spring), and LLWS

(Lowest Low Water Spring).

2.3 Tidal Types Calculation

The harmonic component is also used as a tidal type

analysis at this research location. In determining the

type of tides, it is necessary to calculate the value of

formzahl numbers with the following equation:

𝐹=

𝐴



𝐴



𝐴



𝐴



(4)

Where F = formzahl numbers, 𝐴



and 𝐴



= the

amplitude of a single daily tidal component, 𝐴



and

𝐴



= the amplitude of a double daily tidal

component. classification of tidal types based on the

value of formzahl numbers is divided into 4 types.

Where the classification is a semidiurnal tides (0 <F

<0,25), mixed mainly semidiurnal tides (0,25 <F

<1,5), mixed mainly diurnal tides (1,5 < F <3,0) and

diurnal tides (F> 3,0).

3 RESULTS AND DISCUSSION

3.1 Comparison of Water Level in the

River and the Sea

Based on observations that have been made, it is

known that the water elevation value at the study site

is shown in figure 2 for 75 days from January-April

2020. The river observation locations are selected

based on the area planned as tidal flood protection in

Ujungmanik Village. Whereas the observation

location at sea is based on the connectivity of the flow

with the Parit river. The results of river and sea

elevation are compared in graphical form by

equalizing the MSL value in each data. These results

are shown in Figure 3.

Figure 2: Tidal elevation monitoring locations.

Figure 3: Water levels in the Parit River and Teluk Penyu

Beach in Cilacap.

The results in Figure 3 show the different phases

in the water elevation in the Parit river and Cilacap

Bay Coastal Waters. The pattern of movement of tidal

in the two study sites has the same tendency. The sea

level is higher than the river water level. At ebb

condition, the sea level is also dominantly lower than

the river elevation value. This proves that the tidal

conditions at sea affect the elevation of water in the

river. The graph shows the time of the rise and fall of

the water level in the sea is always faster than the

water level in the river. This proves that there are

differences in the tide and ebb levels in water

elevations in rivers and sea.

3.2 Analysis of Least Square Tidal

Results

Data of water elevation in the Parit River for 75 days

previously obtained shown in Figure 4 was calculated

using the least square method. With the least square

method, the results of 9 tidal harmonic constants are

shown in Table 1.

Tidal Analysis for Planning the Tidal Flood Management and the Moveable Weir, Case Study in Parit River, Kawunganten Cilacap

283

Figure 4: Comparison between observation data and tidal

forecasting results.

Based on the comparison, the graph mentions of

tidal forecasts with primary data obtained, and an

error value of 0,101%. The error value obtained

comes from the least square calculation which ignores

the meteorological influence, so that the astronomical

effect also does not participate in the effect of tidal

generation on the model.

Table 1: Harmonic constants.

Constanta A(m) g

0,457 201,470

0,247 331,730

0,088 94,540

0,179 288,920

0,113 230,300

0,037 176,130

0,040 309,880

0,042 134,240

0,036 306,740

Where A is amplitude and go is a phase. From the

9 harmonic constants that have been obtained in table

1, we get the value of the formzahl number is 0,4148.

With this value, the tidal type at the study site is

classified as a mixed mainly semidiurnal tides

because the value of formzahl numbers ranges from

0,25 <F <1,5. The characteristics of tidal types at this

location occur two times the tide and two times the

tide in a period of 1 day (24 hours). However, the

water level elevation value that occurs is irregular and

has a difference in elevation between two tides and

two ebbs in one day.

From the calculated harmonic constants, we can

get important tidal elevation results at the study site.

MSL (Mean Sea Level) value of 2,48 m, MHWS

(Mean High Water Spring) of 3,184 m, MLWS

(Mean Low Water Spring) of 1,776 m, HHWS

(Highest High Water Spring) of 3,476 m and LLWS

(Lowest Low) Water Spring) of 1,484 m.

In planning LLWS dams it is used as a reference.

So the LLWS value becomes 0. Then the results of

other elevations become MSL (Mean Sea Level)

value of 0.996 m, MHWS (Mean High Water Spring)

of 1.7 m, MLWS (Mean Low Water Spring) of 0.292

m, HHWS (Highest High Water Spring) of 1,992 m

and LLWS (Lowest Low Water Spring) of 0 m. The

tidal graph with reference to +0.00 is LLWS can be

seen in Figure 5.

Figure 5: The water level in the parit river LLWS= 0.

3.3 Infrastructure Analysis with Tidal

Elevations

Peil Scale as a tidal reference is placed under the

bridge. The bridge's elevation based on Peil Scale is

+4,20 m. Based on the receding elevation, the bridge

floor elevation is around +2.72 or around 70 cm from

HHWS. One function of tidal observation and

analysis is to determine the +0.00 LLWS elevation

used as a reference for bathymetry measurements.

The results of bathymetry measurements can be seen

in Figure 6.

Figure 6: Bathymetry in research location  LLWS= 0.

Based on observations of the plains along the Parit

river ranging from +1.00 to + 2.00, so that when the

tides are experiencing tidal inundation as shown in

Figure 7.

ISOCEEN 2019 - The 7th International Seminar on Ocean and Coastal Engineering, Environmental and Natural Disaster Management

284

Figure 7: Tidal flood affected areas.

Based on the results of tidal measurements and

analysis, the elevation of water structures including

weirs, embankment, and floodgates can be determined.

Assuming a maximum tidal height of 1,99 m, the

height of the water structure plus a freeboard (guard

height), for example for embankment and weir is added

1,0 m or about = + 3,0 m.

4 CONCLUSIONS

1. Tides and ebb elevations of water at sea are

always faster than elevations of water in rivers.

This proves that there are differences in the tide

and ebb levels in water elevations in rivers and

seas. The sea level is dominantly higher than in

rivers. Therefore tidal conditions in the sea affect

the occurrence of tidal floods that occur to the

inhabitants along the river area.

2. Formzahl numbers obtained from tidal analysis

in the Parit River amounted to 0,4148, from this

value known tidal types at the study site are

classified as mixed mainly semidiurnal tides

because the value of formzahl numbers ranges

from 0,25 <F <1,5.

3. Tidal elevation obtained from the calculation of

harmonic constants is the MSL (Mean Sea Level)

Value of 0,996 m, MHWS (Mean High Water

Spring) of 1,7 m, MLWS (Mean Low Water

Spring) of 0,292 m, HHWS (Highest High Water

Spring) of 1,992 m and LLWS (Lowest Low

Water Spring) of 0 m.

4. The bridge's elevation based on Peil Scale is +4,20

m. Based on the receding elevation, the bridge

floor elevation is around +2.72 or around 70 cm

from HHWS. So in determining the height of the

weir can be used +3.0 m elevation to prevent high

tides flowing through the Parit River.

ACKNOWLEDGEMENTS

Our gratitude goes to the Directorate of Research and

Community Service, the Indonesian Ministry of

Research, Technology and Higher Education for

funding this research, we also thank all the residents

and officials of the Ujungmanik village involved, and

all the stakeholders who have supported and

participated.

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