thesis final exam sedimentation study of rejoso … · wse=hwl+ru . proposed jetty design...

THESIS FINAL EXAM

SEDIMENTATION STUDY OF REJOSO JETTY USING

NUMERICAL MODEL

By :

Ardiansyah Fauzi (115876)

(Joint Degree Master Student AIT-ITS)

Examination Committee : Prof. Mukand S. Babel (Chairperson)

Dr. Sutat Weesakul (Co-chairperson)

Dr. Sangam Shrestha

Dr. Akiyuki Kawasaki

1

Location of study

6000 m

Introduction

2

Location of Study

Rejoso Estuary

3

Introduction

Jetty Plan

Layout of jetty plan

- Deposited area from 2004-2010 is

26283.9685 m2

4

Introduction

Flood location around

Rejoso River

• Flood depth varies from 30-50 cm

• Flood duration is ± 4 hours

• Occurred frequently1-2 times in a year

Flood in Jarangan and

Kedungbako village

5

+ 2.603

35,60

3,14

3,24

+ 2.493

39,50

Cross Section II-II

Not To Scale

Cross Section I-I

Not To Scale

Introduction

I I

II II

Deposition in the estuary, which reduce river discharge

capacity

Flood occurs regularly in the upstream area.

6

Statement of Problem

Introduction

7

WSE=HWL+Ru+Freeboard WSE=HWL+Ru

Proposed jetty design

(Wiratman, 2010)

Breaking wave location

Breaking wave

location with

H=0.9 m; T=4 m Study location

Overall objective

To determine the effect of jetty construction in the

hydrodynamics and sediment transport

Specific objectives

To determine the coastal climate (current and sedimentation)

due to jetty construction

To verify and propose geometric and length of jetty

Objectives of the Research

8

Introduction

Dataset

9

Methodology

No. Type of Data Periods Frequency Stations Source Coordinates

1 Wind data 2004-2010 Hourly 1 Station

-W1

- BMKG 7° 37.711' S 112°

56.547'E

2 Topography

and

Bathymetry

2010 DWR

3 Tidal data 2010 (Mike

Predicition)

October

2010 (Obs)

Hourly 2 Stations

- T1

- T2

- MIKE

Software

- Obs

7° 33.451' S 112°

58.481'E (T1)

7° 37.479'S 112°

57.340'E (T2)

4 Sediment data

- Grain Size

- Suspende

d load

Oct 5th 2010 1 day

measurement

2 Stations

-S1

-S2

DWR 7° 37.475' S 112°

57.368'E (S1)

7° 37.437' S 112°

57.484'E (S2)

5 Current Oct 5th 2010

(10 hours)

Hourly 2 Stations

-C1

-C2

DWR 7° 33.451' S 112°

58.481'E (C1)

7° 37.462'S 112°

57.473'E (C2)

6 Rain data 2001-2010 Daily 7 Stations DWR

7 Discharge

recording in

river

2010 Daily 1 Station

- Q1

DWR 7° 38.468‘ S, 112°

57.245'E

10

(Source : Google Earth)

Methodology

11

(Source : BMKG)

(Source : Observation)

Methodology Wind Rose(W1 Location)

Tidal (T1 Location)

(Source : MIKE Prediction)

Tidal (T2 Location)

12

Methodology

(Source : Department of Water Resources)

(Source : DWR)

Catchment Area Characteristic

Observed River Discharge (Q1 Location)

Average Wind Speed (W1 Location)

(Source : BMKG)

Monthly averaged

Methodology

13

14

Results and Discussion

Model Setup

Water Surface Elevation (WSE)

- For calibration : WSE on October

2010

- For Scenario : WSE on January

2010

Flow Rate (FR)

- For calibration : FR on Oct ober 2010

- For scenario : FR on January 2010

Model Domain

15


Consist of :

- 9322 triangular elements

- 4 quadrilateral elements

- 19320 nodes

The digital elevation is

interpolated linearly

with elements.

16

A

B Results and Discussion

Cross section bed elevation of the sea

A

B

17

Model Calibration

Current velocity observation

Current velocity and water surface observation

T2, C1 C2


Observation point for calibration

18

Results and Discussion Model Performance

Tidal (T2)

Current Velocity Current Velocity (C1)

Current Velocity (C2)

Eddy

Viscosity (Pa-

sec)

Manning RMSE (m) R

Tidal (T2) 4000 0.03 0.0023 0.996

Velocity 1 (C1) 4000 0.03 6.48804E-05 0.9477

Velocity 1 (C2) 4000 0.03 0.0006 0.8143

Parameter Statistical performance

Calibration

19

Sensitivity Analysis

Simple channel with single

material.

- Length is 800 meters

- Width is 100 meters.

Boundary condition in inlet is

100 m3/s and water surface

elevation in oulet is 6 meters.

100m3/s 6 m


Simple Channel

This sensitivity analysis is done to obtain

which parameters give great effect in the

model.

20

Constrained flume with single

material.

- Length is 800 meters

- Width is 100 meters.

- Constricted to 20 m wide

through the middle

Boundary condition in inlet is

100 m3/s and water surface

elevation in oulet is 6 meters.

100m3/s 6 m


Constrained Channel

21


Simple Channel

22


Constrained Channel

23

Sensitivity Analysis at the Model Domain

Cross section for sensitivity analysis in ocean

A

B


Observation arc for sensitivity analysis at the ocean

24


Water Surface Elevation Flow Velocity

A B

A B

A B

A

B

25


D

C

Long section for

sensitivity analysis

Observation arc for sensitivity analysis at the river

26

Water Surface Elevation Flow Velocity


27

Jetty Selection Criteria Designed length of jetty is 1170 m. The length

jetty is planned up to the depth before

breaking wave. It aims to bring the sediment

supply to the area with calm current (before

breaking waves), so there is no deposition in

the area of breaking waves that can cause

siltation of estuary (Wiratman, 2010).

Criteria for Rejoso jetty :

1. Accommodated the sediment deposition.

2. Less maintenanced.

3. Accommodated natural processes in the

estuary.

Jetty function :

1. To prevent sedimentation in the estuary

2. To move sedimentation process from the

the estuary to the sea

3. To prevent longshore sediment transport

block the river mouth

(Source : The Overseas Coastal Area

Development Institute of Japan, 2002)


Layout of jetty

28

Model Simulation

There are 4 scenario model simulation as follows:

1. No jetty

This condition is purposed to simulate the existing condition

2. Jetty length 100%

This condition is to simulate the condition with original proposed design from local government

3. Jetty length 50%

By reducing the length of jetty by 50%, it is expected to show the condition where proposed jetty

design is based on breaking wave, but the actual condition in Rejoso estuary is dominated by river

discharge. It is expected that the length of jetty no need too long until before breaking wave

location.

4. Jetty length 50% with constrained

Length of jetty 50% from proposed design with constrained 15 meter in the jetty tail end is used

in model by considering the function of jetty is only to maintain the the sedimentation process in

the estuary, there is no function for navigation canal. By this assumption, it is expected the

velocity inside the jetty will be higher and it can flush the sediment inside the jetty better.


29


Global current condition at

time step 138 hours (spring

tide condition)

Near estuary current

condition at time step 138

hours (spring tide

condition)

Scenario 1

30



time step 144 hours (neap

tide condition)


condition at time step

144 hours (neap tide

condition)

Scenario 1

31

Suspended load at time step

138 hours (spring tide

condition)



condition)


Scenario 1 (no jetty)

32

Bed change at time step 720 hours


Scenario 1 (no jetty)

33


Scenario 2 (Jetty 100%)



tide condition)




condition)

34





tide condition)




condition)

35



condition)



condition)



36




37





tide condition)




condition)

38





tide condition)




condition)

39



condition)



condition)



40




41


Scenario 4 (Jetty 50% constrained)



tide condition)




condition)

42


Scenario 4 (Jetty 50% constrained)



tide condition)




condition)

43



44


Velocity distribution at the mouth of jetty

45

E

F

Scenario 1

Scenario 3

Scenario 2

Results and Discussion Observation at the river before and after

jetty construction

K

L

G

H

I

J Scenario 4


46

Time step 138 hours (spring tide)

Time step 144 hours

47

Time step 144 hours (neap tide) Results and Discussion

48

Results and Discussion BED CHANGE IN 720 HOURS TIME STEPS

Scenario 1

Scenario 2

49


Scenario 3

Scenario 4

BED CHANGE IN 720 HOURS TIME STEPS

50

WATER SURFACE CHANGE USING RETURN PERIOD DISCHARGE IN 720 HOURS TIME

STEPS

at time step 138 hours

(spring tide condition)

at time step 144 hours

(neap tide condition)

CONCLUSION The effect of jetty construction will block the the current flow from

east to west and cause turbulence in the west side of jetty and reduce the current velocity up to 56% in the west side of jetty. The sedimentation process in the estuary can not be simulated well, because it is difficult to apply radiation stress in the model domain.

The result in scenario 2-4 provides weakness and advantages. If using jetty length 100%, it will be good in moving sediment deposition from estuary to the offshore, but the length of jetty is no need that long because Rejoso estuary is river dominated, and also the longshore sediment transport is difficult to move bypass the jetty. If using jetty length 50 % with unconstrained, the velocity and the water surface elevation changes in the river is not much different with jetty length 100%, it is showed that with jetty length 50% from proposed design is enough to maintain condition in the river. If using jetty length 50% with constrained, the velocity in the river is higher than the other simulation, but the changes of water surface elevation in the river is need to be noticed. By that condition, the jetty length 50 without constrained can be better than proposed design and jetty with constrained, because considering the velocity and water surface elevation changes in the river is not quite different with existing condition.

51

Conclusion

It needs time series sediment concentration data to represent the

process sedimentation more representatively with actual

condition.

Wave-current simulation is needed to make more representative

model for longshore sediment transport

52

Recommendation

RECOMENDATION

PUBLICATIONS

1. Studi Dampak Pembangunan Jetty Kali Rejoso Pada Daerah

Pantai Dengan Menggunakan Model Numerik. Seminar

Nasional Aplikasi Teknologi Prasarana Wilayah 2014

53

55

Regional

Domain

Local Domain


Regional domain using grid dimension Dx=Dy = 80 meters

Local domain using grid dimension Dx = Dy = 2 meter.

Wave Model Setup

56

Spectral energy with H=0.93 m, T=6.14 s


Specified Spectrum

1-D Transformed

Spectrum

1-D Transformed

Spectrum

Zero Spectrum

Boundary Conditions

57


Regional Domain Result

Local Domain Result

thesis final exam sedimentation study of rejoso … · wse=hwl+ru . proposed jetty design...

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