Distribution of Current and Temperature at Welang Estuary,

Pasuruan

Inayatul Lailiyah

, Suntoyo

, Wahyudi

, Fauzy Nasruddin

and Liliane Geerling

Department of Ocean Engineering, Faculty of Marine Technology, Institut Teknologi Sepuluh Nopember (ITS),

60111 Surabaya, Indonesia

Department of Water Resource Management, Public Works and Water Source East Java Province, Surabaya, Indonesia

Delta Academy, Water Management, HZ University of Applied Sciences, Middelburg, 4331 NB, The Netherlands

Keywords: Estuary, Temperature Distribution, Current Velocity, 3D Modelling, Welang River.

Abstract: Welang river estuary has many benefits to the surrounding community, i.e for the fish and shrimp farming.

Estuary ecological management in this area is important. In which, it is necessary to understand the dynamics

of the waters so that the estuary area can be managed properly. The purpose of this study was to determine

the characteristics of the welang estuary using 3D modeling. Welang river estuary influenced by tidal

conditions. The current pattern that occurs in the welang estuary moves from southeast to northwest. Current

velocity around the welang estuary at the surface of the water tends to be greater than at the bottom of the

water. This is because of the influence of the wind. The horizontal temperature distribution tends to be uniform

and vertically shows no thermocline layer at the welang estuary.

1 INTRODUCTION

The coastal region of Indonesia has a fairly extensive

estuary area, one of which is on the north coast of

Java, some researchers have studied related to the

estuary environment in several locations, e.g.,

Porong, Wonorejo and Wonokromo river. (Suntoyo

et al., 2015; Suntoyo and Sakinah, 2017; Sakinah et

al., 2017; Pahlewi et al., 2017; Kauhl et al., 2018).

Welang watershed is located in Malang Regency,

Regency and Pasuruan City. The Welang River

empties into the Kraton Subdistrict, Pasuruan

Regency which is directly related to the Madura Strait

(Febriyanto et. al., 2018). Welang estuary is an

estuary ecosystem that has an important function as a

biota habitat, such as fish. In addition, this area is used

by local residents as fish and shrimp ponds. The more

activities that occur in estuary areas, the area will

have an influence on the quality of estuarine waters,

directly or indirectly.

Until now, some informations regarding the

characteristics of the welang estuary is currently

limited. So the need for further research in the estuary

area to be able to develop its designation, such as

ports, transportation routes, tourist areas and fish

farming. The characteristics of flow patterns,

temperature and salinity are important parameters in

water dynamics that have an influence on water

circulation (Pahlewi et. al., 2017; Suntoyo and

Sakinah, 2017; Sakinah et al., 2017).

Determination of estuary type is the initial stage in

carrying out development planning in the estuary by

taking into account its characteristics such as current,

temperature and salinity. Therefore the purpose of this

study is to analyze the characteristics of the waters in

the welang estuary based on the parameters of current,

temperature and salinity and can determine the type of

estuary in the estuary of the Welang.

Current and temperature distribution were

modeled by using 3-dimensional models in order to

explain the distribution horizontally and vertically.

Furthermore, these results was analyzed to explain

the characteristics of Welang estuary waters.

2 STUDY AREA

The research location is in the Welang River estuary

in the Kraton and Ketug Pasuruan Districts. Welang

River itself crosses Malang Regency, Pasuruan

Regency and Pasuruan City, East Java Province

empties into Madura Strait.

Lailiyah, I., Suntoyo, ., Wahyudi, ., Nasruddin, F. and Geerling, L.

Distribution of Current and Temperature at Welang Estuary, Pasuruan.

DOI: 10.5220/0010218802570262

In Proceedings of the 7th International Seminar on Ocean and Coastal Engineering, Environmental and Natural Disaster Management (ISOCEEN 2019), pages 257-262

ISBN: 978-989-758-516-6

257

The modeling location in this study is shown in

Figure 1, where the blue area indicates the modeling

area. Direct measurements consist of current,

temperature and salinity carried out at 5 sampling

stations with 3 different depths (0.2d, 0.6d and 0.8d).

The model simulation was carried out for 6 months,

from July 2019 to January 2020. Geographically, the

Welang Estuary is located at 112,861⁰E - 112,896⁰E

and 7,584⁰S -7,590⁰S.

3 METHOD

The methodology used in this research, the first step

is the study of literature to support the study to be

carried out, followed by the collection of data which

includes primary data and secondary data. Primary

data were obtained by performing direct

measurements in the field which included

temperature, flow velocity and salinity data. Whereas

secondary data was obtained from various related

agencies and this data used for input simulation

models such as bathymetry, tides, wind, and river

discharge data. After data collection, the next step is

to process bathymetry data which will become input

data in the simulation of current and temperature

distribution using 3D modeling where the output is

current and horizontal and vertical temperature

distribution. Modeling and simulation was done using

computer software with a simulation time of 30 days

or 720 hours in November 2019, to obtain the good

results, the model validation was conducted. Then

analyze the res ults and finally conclusions.

4 MODEL VALIDATION

The results of the modeling of the current pattern are

validated using tidal data obtained from measurement

results on November 1, 2019 - December 1, 2019 at

the Grati Power Plant and the current velocity

measured at point St 21 (Figure 2) by using current

meter. In general, the results of the model and

measurement data show a trend that is equal to the

MAPE (Mean Absolute Percentage Error) value of

0.35% (Figure 3). Current measurements are carried

out on 14 November 2019 at 12.00-21.00 WIB within

all three depths (0.2d, 0.6d, and 0.8d) using a current

meter (Figure 4). The results of the current velocity

from the three depths are then averaged. The results

of the current validation at point St 21 show a MAPE

value of 27.5%, while the RMSE value is below 1.00.

Model validation is acceptable because the error is

still below 30%. The validation of current velocity

modeling is classified as Reasonable forecasting.

Figure 1: Study Area Including of Observational Stations (Google Earth).

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Figure 2: Validation of Current Velocity at Point St 21.

Figure 3: Comparison of Tidal Elevations between Forecasting Data and Model Results.

5 RESULTS AND DISCUSSION

The modeling results presented in this paper are the

horizontal and vertical distribution of velocity and

temperature. From the simulation results, the sea level

with the highest tide is 1.052 m in step 384, while the

lowest tide with -1.132 m in step 366. Where the

highest tide conditions occur on November 17, 2019

at 00.00 WIB and the lowest tides occur on November

16, 2019 at 06.00 WIB. Based on tidal data analysis,

the Welang estuary is a valid semi-diurnal tidal type

(Figure 4).

At highest tide conditions, the current pattern

moves from southeast to west toward the estuary,

while the current pattern at lowest ebb moves east

towards the sea. The frequency of the direction

current is more dominant in the west-northwest

direction, this is due to the east monsoon wind pattern

as well as shown by (Sugianto, 2009). The current

velocity at point 18 show that the highest tide occurs

between 0-0,06 m/s and the lowest tidal current

between 0.015-0.105 m/s presented in Figure 5.A and

5B. The current velocity at the highest tide tends to

be lower than at lowest ebb. The Reason is at high

tide, seawater moves into the river and at the same

time, the river water pushes upstream. At lowest ebb,

currents tend to be higher because the water just

Distribution of Current and Temperature at Welang Estuary, Pasuruan

259

pushes out towards the river mouth and increases the

current velocity.

From the distribution of current at the highest tide

and lowest ebb shows that the value of the current

speed at the top is greater than at the bottom of the

waters. this is due to the effect of the wind coming

from the southeast as well as the bottom shear stress

reduced the velocity in the sea bottom (Figure 6).

In the vertical distribution, reviewed at 2 points

namely point IP1 and IP2 (see Figure 7) which are

around the point 18 estuary. Current distribution at

the highest tide conditions (384 step), at a distance of

0-80 m from IP 1, the speed current is varies from

surface to bottom waters. On the surface the current

velocity ranges from 0.008 to 0.096 m/s while the

current velocity at the bottom of the waters is around

0.008-0.072 m/s. at a distance of 80-220 m, uniform

current velocity distribution from surface to bottom.

Where the current speed is around 0-0.016 m/s

(Figure 8 A.).

Current distribution at the lowest ebb condition

(step 366), at a distance of 0-80 m from IP 1, the

current speed is varies from surface to bottom of the

waters. On the surface the current speed ranges from

0.048-0.120 m/s. while at the bottom of the waters,

the current speed is around 0-0,024 m/s. At a distance

of 80-220 m, the current surface velocity values are

around 0-0,048 m/s and at the bottom of the waters

the current speed is around 0-0,032 m/s (Figure 8.B).

At the highest tide conditions, high temperatures

from the sea towards the river mouth. The

temperature in the river body area ranges from 30.10-

30.50 °C. Whereas in river mouths the temperature is

around 30.55-30.65 °C, and at sea temperatures

above 30.65 °C (Figure 9.A.). The pattern of

temperature distribution at the lowest ebb conditions

shown in Figure 9.B. In the river body area, the

temperature value is around 30.10-30.2 ° C, while the

temperature value in the river mouth area is around

30.2-30.45 ° C and in the sea area the temperature

value is around 30.5-30.7 ° C.

Overall the temperature at highest tide in the

estuary area is caused by the push coming from the

sea which has high temperature. Whereas at lowest

ebb the temperature in the estuary tends to be low

because at ebb the flow is only influenced by the river

discharger that goes to the sea, so that the temperature

carried from the upstream of the river is low towards

the sea gives the effect of decreasing the temperature

in the estuary to the sea

The distribution of temperature at the highest tide

conditions at a distance of 0-20 meters, the

temperature value is around 30.58-30.61 ° C. at a

distance of 20-210 meters the temperature value is

around 30.61-30.64 ° C and the temperature value at

a distance of 210-280 meters is around 30.64-30.67 °

C (Figure 9.A). The distribution of temperature at the

lowest ebb conditions at a distance of 0-110 meters

around 30.25-30.28 ° C, while at a distance of 110-

220 meters the temperature value tends to vary at

around 30.31-30.52 ° C (Figure 9.B).

In general, the vertical temperature distribution

pattern in both conditions in the welang estuary tends

to be uniform from top to bottom. Although the value

of the surface layer is greater than the middle and base

layers. This is due to the influence of direct sunlight.

Distribution of temperature from surface to base there

is no thermocline layer. This is because in this area

including shallow water so the temperature tends to

be uniform as well as shown by (Alosairi et al. 2018).

Figure 4: Water Suface Elevation.

Highest tide

Lowest ebb

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Figure 5: Horizontal Current Distribution in A: the Highest Tide, B: the Lowest Ebb.

Figure 6: Wind Rose Direction and Speed Current

Distribution.

Figure 7: Position IP1 and IP2 Cross-section.

Figure 8: Horizontal Temperature Distribution in A: the Highest Tide, B: the Lowest Ebb.

Distribution of Current and Temperature at Welang Estuary, Pasuruan

261

Figure 9: Horizontal Temperature Distribution in A: the Highest Tide, B: the Lowest Ebb.

6 CONCLUSION

The current pattern that occurs in the welang estuary

is moving from the southeast toward the northwest.

The speed current around the welang estuary at the

surface of the water tends to be greater than at the

bottom of the water. This is due to the effect of the

wind. The horizontal temperature distribution tends to

be uniform and vertically shows there is no

thermocline layer in the welang estuary and the

temperature distribution from the surface to the

bottom does not differend so that the distribution is

evenly distributed only slightly higher on the surface

due to direct sunlight so that the surface is hotter

compared to the bottom .

ACKNOWLEDGEMENTS

Authors would like to thank the Centre of Research

and Development of Marine and Coastal Resources,

the Ministry of Marine Affairs and Fisheries,

Republic of Indonesia for providing the facilities of

DHI’s Mike 21/3 model and the Water Resources

Public Works Department of East Java Province for

providing some informations and data related the

Welang River.

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