FIELD EXPERIMENTAL STUDY ON A SOFT PROTECTING METHOD FOR COASTAL EROSION PREVENTION

1

National Cheng Kung University , Taiwan Ta-Hsiung Peng Ph. D. Candidate 2010/09/11

Content

INTRODUCTION

RESEARCH METHODOLOGY

RESULTS AND DISCUSSIONS

CONCLUSIONS

2

INTRODUCTION 1/3

The construction of rigid protection methods is always expensive and time consuming, and in some cases, not very effective on coastal protection due to a fail in sediment deposition.

A flexible device was introduced to protect coastline. The flexible device has less impact on environment, less time of construction and much less cost of construction.

3

INTRODUCTION 2/3

The flexible device is a combination of flexible wire nets and stack of rings made of used vehicle tires and soft blades on its surfaces.

This flexible wire net is placed in between two stack of rings. The stack of rings is mainly used to hold the flexible wire nets and the flexible wire net is mainly used to reduce wave energy and helps to deposit sediments in coastal area.

4

INTRODUCTION 3/3

For a field experimental study, a flexible device to protect coastline has been set up at the Shuang-Chun coastal area (Fig. 1) in Tainan County since June 10, 2009. Till now already set up two devices and No.3 device is progressing.

5

Fig. 1 Shuang-Chun coastal area (Field study site)

Convex

Concave

6

Fig. 2 Comparison of the shorelines based on satellite images taken on 2007/2/28 (pink line) and 2009/1/3 (red line).

Fig. 3 Comparison of the shorelines based on satellite images taken on 2005/5/27 (pink line) and 2009/1/3 (red line). 7

RESEARCH METHODOLOGY

This field experiment has set up in Shuang-Chun coastal area in Tainan County. It was a submerged like offshore flexible breakwater that is made up of a flexible wire net and two stacks of rings (used vehicle tires) with soft blades on its surfaces.

This flexible wire net was placed in between two stacks of vehicle tires. The stack of used vehicle tires with a steel wire gabion filled with stones inside was used to hold the flexible wire net, as shown in Fig. 4.

8

Fig. 4 Stake of used vehicle tires

Fig. 5 Wire nets with soft blades

Fig. 6: Bottom row of the wire net attached with vehicle tires

9

Fig. 7 Schematic diagram of the arrangement of the flexible breakwater used the field experiment study

10

RESULTS & DISCUSSIONS 1/7

The above-mentioned flexible device of coastal protection has been set up at the Shuang-Chun coastal area in Tainan County since June 10, 2009.

The function of the device has been examined by Typhoon Linfa during June 19~22, 2009 and by Typhoon Morakot during August 6~10, 2009.

11

Measured contour by total station instrument

12

RESULTS & DISCUSSIONS 2/7

Location Point A Post 1 Post2 Post 3 Post 4 Post 5 Post 6 Point B

Before setup,

H1(2009/5/17)

-0.619 -0.820 -0.835 -0.816 -0.801 -0.660 -0.715 -0.815

After Linfa,

H2(2009/7/26) 0.115 -0.123 -0.141 -0.064 -0.011 -0.107 -0.469 -0.246

After Morakot,

H3(2009/8/15) -0.067 -0.104 -0.072 -0.044 -0.027 -0.058 -0.042 -0.046

H (m) 0.552 0.716 0.763 0.772 0.774 0.602 0.673 0.769

Table 1. Surface elevation measurements before and after the setup of the device

13

RESULTS & DISCUSSIONS 3/7

Fig. 8 Surface elevation measurements before and after the setup of the device14

RESULTS & DISCUSSIONS 4/7

Distance from coastline (m) 0 10 20 30 40 50 60 70 80 90 100 110

Before setup, H1(2009/5/17) 0.681 0.383 0.085 -0.213 -0.511 -0.746 -0.956 -1.176 After Linfa, H2(2009/7/26) 1.62 1.132 0.92 0.7 0.48 0.26 0.04 -0.14 -0.183 -0.402 After Morakot, H3(2009/8/15) 1.67 1.316 0.961 0.673 0.482 0.292 0.105 0.048 0.015 -0.056 -0.167 -0.35

15

RESULTS & DISCUSSIONS 5/7

Fig. 9 Coastal bed evolution after Typhoon Linfa and Typhoon Morakot

16

RESULTS & DISCUSSIONS 6/7

The contour line (red) was measured at the study site before installing the device (2009/5/17). After the attack of Typhoon Morakot, another measurement was conducted to obtain the bed contour line (black). The comparison of of these two measurements showed that the shoreline (H=0) has shifted about 44 meters from the land side toward the offshore.

The sedimentation is obvious after the set up of the flexiable soft breakwater and the land reclamation area has been approximately 10,000 m.

17

RESULTS & DISCUSSIONS 7/7

158750 158800 158850

2580450

2580500

2580550

2580600

2580650

2580700

18

Fig 11. Variation of shoreline in the area of field experiment study.

19

photo during setup process

20

No.1 device

21

Working in winter(2009/12/30)

22

The pictures after Linfa typhoon and Morakot typhoon

photo from southern direction after Linfa typhoon

photofrom northern direction after Linfa typhoon

Photo from southern direction after Morakot typhoon

Photo from northern direction after Morakot typhoon, the red arrow means sea ward from the device

23

00.1

0.1

0.1

0.2

0.2

0.3

158750 158800 158850 1589002580400

2580450

2580500

2580550

2580600

2580650

2580700

2580750

-1.9-1.8-1.7-1.6-1.5-1.4-1.3-1.2-1.1-1-0.9-0.8-0.7-0.6-0.5-0.4-0.3-0.2-0.100.10.20.30.40.50.60.70.80.91

0

0.1

0.1

0.1

0.2

0.2

158750 158800 158850 1589002580400

2580450

2580500

2580550

2580600

2580650

2580700

2580750

-1.9-1.8-1.7-1.6-1.5-1.4-1.3-1.2-1.1-1-0.9-0.8-0.7-0.6-0.5-0.4-0.3-0.2-0.100.10.20.30.40.50.60.70.80.91

0

0.1

0.1

0.1

0.2

0.2

0.3

158750 158800 158850 1589002580400

2580450

2580500

2580550

2580600

2580650

2580700

2580750

-1.9-1.8-1.7-1.6-1.5-1.4-1.3-1.2-1.1-1-0.9-0.8-0.7-0.6-0.5-0.4-0.3-0.2-0.100.10.20.30.40.50.60.70.80.91

24

Sediment deposited in different period

Measure date8/15/2009-12/11/2009

Measure date08/15/2009-01/14/2010

Measure date08/15/2009-02/09/2010

::No.1 device

groyne

::

::

No.1 device

groyne groyne

No.1 device

difference (m)

difference (m)

difference (m)

24

Photo from A point to southern direction Left picture: the beach eroded and bamboo exposed(2009/1/5)

Right picture: the sediment deposited and buried bamboo(2010/1/18)

25

Compare the condition at 200m southern far away of the date 2009/1/5 and 2010/1/18

26

Photo from A point to northern directionLeft picture: the beach eroded and bamboo exposed(2009/1/5)

Right picture: the sediment deposited and buried bamboo(2010/1/18)

27

Photo from A point to eastern directionLeft picture: the beach eroded and roots exposed after Linfa typhoon (2009/6/22)

Right picture: the sediment deposited and buried to the waist of tree, formed a number of parallel sand dunes in forest zone(2010/2/2)

28

Photo from B point to northern direction Left picture: naked four row bamboo after Linfa typhoon(2009/6/24)

Right picture: the original bamboo buried only remaining half of the original row of four rows at same place(2010/2/2)

29

Photo from B point to southern direction Left picture: exposed four rows of bamboo after Linfa typhoon(2009/6/24)

Right picture: the original bamboo buried only remaining one of the original row of four rows at same place(2010/2/2)

30

31

The arrangement of No.2 device and No.3 device

Now the second device has already been set up on 2010/5/17 which was departed 50m away from the first one and worked very well. The sediment deposition rate was double than that of first one. The deposited sediment already recovered the coastal erosion to the original position and the coastline shifted to the sea side. The third stage is now under construction and would be setup very soon. The final shape of the device would be like following drawing.

Fabrication of No. 2 device

Vehicle tire with reduced energy wire

Triangle gabionReduced energy net

Spring Pipe

32

N0.2 device assembled

33

No.2 device assembled

34

No.2 device assembled

35

No.2 device

36

No.2 device working(2010/8/28)

37

No.2 device working(2010/8/28)

38

Compare sediment deposited

The photo was taken on tide down condition (2010/5/29).

The device was buried in sediment up to half of the height (2010/9/7).

39

Compare sediment deposited

The bamboos near the device & the height was 105cm when assembled (2010/5/1).

The same bamboo remained 45 cm high at the same position (2010/9/7).

40

ecology

Covered with shells(2010/8/9) Enlarge(2010/8/9)

41

Photo from model airplane

Device setup (2010/8/9) Photo from air by using remote control(2010/8/9)

42

Comparison of coastal area between without and with protection device setup

43

The beach eroded without device(2008/9/24)

0.5

1

158750 158800 158850 1589002580400

2580450

2580500

2580550

2580600

2580650

2580700

2580750

-1-0.8-0.6-0.4-0.200.20.40.60.811.21.41.61.822.22.42.6

44

Sediment deposited when No.1 device(blue),No.2device(red)set up(photo 2010/8/9)

-1.2

-0.2

-0.2

0.8

0. 81.8

158700 158800

2580000

2580100

2580200

2580300

2580400

2580500

2580600

2580700

-2.2-1.8-1.4-1-0.6-0.20.20.611.41.82.22.633.4

15 870 0

1 5880 0

2 5 80 00

02 58

0 100

2 5802 0

02 58

03 00

25 80 4 0

025 8

0 500

25 80 60

02 58

0 700

-1-0.8-0.6-0.5-0.4-0.200.10.20.40.50.60.811.11.21.41.51.61.822.12.22.42.6

No.1

No.2

45

CONCLUSIONS 1/3

The installment of the flexible breakwater for coastal protection against sediment erosion is a three years project supported by the National Science Council in Taiwan, starting from the August 2008 to July 2011.

It was designed to complete in the first year and the length of flexible breakwater was designed as 50 meters. The flexible breakwater for the first year and second year project has been setup, been running, and been challenged by Typhoons Linfa and Morakot.

46

CONCLUSIONS 2/3

The results have proved that this flexible breakwater was strong enough against the severe typhoon attacks, and showed that it has trapped sediment effectively and deposited on coastline. The depth of sediment deposition around the device was about 0.5 to 0.8 meters.

The second-year project already finished on May17th,2010. The same length 50m of flexible breakwater was set up. The device was buried in sediment up to half of the height (2010/9/7).

47

CONCLUSIONS 3/3

And the sediment deposition rate was double than that of first one. The deposited sediment already recovered the coastal erosion to the original position and the coastline shifted to the sea side. The third stage is now under construction and would be setup very soon. The field experiment results show that this flexible breakwater significantly protect the coast and make sediment be deposited, also make land reclamation significantly.

48

Thanks for your attention

49

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49