Performance of Vetiver Grass in Protecting Embankments on the Bangladesh Coast against Cyclonic Tidal Surge

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1 5 th National Conference on Coastal and Estuarine Habitat Restoration Preparing for Climate Change: Science, Practice, and Policy Performance of Vetiver Grass in Protecting Embankments on the Bangladesh Coast against Cyclonic Tidal Surge M. Shariful Islam & Arifuzzaman BUET Mohammad SHARIFUL Islam, PhD Associate Professor Department of Civil Engineering, BUET, BANGLADESH

2 Brahmaputra river Ganges Meghna Area: sq km Population: 144 million GNI: 337 US dollar (2009) Bangladesh Sundarban

3 Cyclone Vulnerable Area of Bangladesh

4 Background About 28% of the population of Bangladesh lives in the coastal regions. The country has over 4,000 km of coastal embankments and 24,000 km of rivers situated on alluvial plain easily eroded by rainfall, river currents and wave action etc. Embankments are safeguard against inundation, intrusion of saline water etc. Embankments are also the first and immediate defense against storm surge and flood. So, these should be protected against such natural hazards.

5 Background Unfortunately our State budget is never sufficient which confines rigid structural protection measures to the most acute sections, never to the full length of the river bank or coastline and embankment. This BANDAGE APPROACH compounds the problem. This hard engineering structures makes the scenic environment unpleasant and helps only to transfer the problem from one place to another place, to the opposite site, or downstream Establishment of vegetation as a soft bioengineering technique to rigid or hard structures accepted all over the world due to its low cost, longevity and environment friendliness.

6 Objectives To find out the causes of coastal embankment failure and common practices for their protection. To search the most suitable vegetation for strengthening the embankment in Bangladesh coast against tidal surge and flood. To determine the in-situ shear strength of Vetiver grass (Vetiveria zizanioides) rooted soil. Finally, to compare the strength of rooted soil with that of soil without root.

7 Courses of Recent Major Cyclones Cyclone Vulnerable Area of Bangladesh

8 6-7 m 3-4 m Cyclone Vulnerable Area of Bangladesh 4-5 m 5-6 m Height of poldar block, IWM

9 Cyclone Sidr 2007: BUET Team BUET team after cyclone SIDR 2007 Wind speed: 250 km/hr Economic loss: 3.1 billion US dollars

10 Cyclone Sidr 2007: JSCE Team Surveyed inundation height and depth at Rayend bazar

11 Cyclone Sidr 2007: JSCE Team

12 Strength of Tidal Surge Water level A school building 2 to 3 km away from the river damaged by cyclone SIDR 2007

13 Embankment Failure: Reasons for Failure

14 Embankment Failure: Reasons for Failure Lack of compaction

15 Embankment Failure: Reasons for Failure

16 Embankment Failure: Reasons for Failure Weak portion of an embankment washed away by cyclonic storm surge

17 Coastal Embankment: Reasons for Failure Embankments washed away by cyclonic storm surge

18 Coastal Embankment: Reasons for Failure Embankments washed away by cyclonic storm surge

19 Embankment Failure: Scour around Trees

20 Embankment Failure: Uprooting of Trees

21 Embankment Failure: Uprooting of Trees Barrier for transferring relief during the disaster.

22 Kuakata sea beach

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24 Performance of Revetment Structure Costly CC blocks! Strong Revetment??

25 Performance of Revetment Structure

26 Performance of Revetment Structure Just after 2/3 months of placement

27 Performance of Protective Measures Costly geotextiles!!

28 Performance of Protective Measures Geo-bags

29 SIDR 2007: Washed Away Houses

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32 SIDR 2007: Washed Away All Family Members

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34 Reasons of Embankment Failure Erosion due to rain splash and wave action Overtopping of cyclonic storm surge Inaccuracy of construction for side slope or the surface embankment Overturning or uprooting of trees Poor construction and maintenance practice The high trees overturned, but low height tress seldom overturned. So, coconut trees and guava trees which will be useful for the local peoples are good for embankment protection. of

35 Social and Economical Losses due to Embankment Failure Loss of lives and property Damage of houses due to cyclonic storm surge Inundation of agricultural land and living areas Collapse of poultry and fisheries sector Highway transportation system cutoff Saline water contamination and adverse effect on agriculture

36 Possible Low-cost Alternatives? Compaction of embankments soil in layers? Vegetation by grass seeding or trees and shrubs? Vegetation with geo-jute? etc.????

37 Conservation Research Institute, 1995 Root Length of Grass Root length is up to 14 ft

38 Is it Vetiver??? 3.4 m Root system Root length (after 9 months)

39 Vetiver in Slope Protection Vetiver hedgerows Mechanism Potential shallow slip surface (1 to 1.5) m deep Vetiver roots

40 Why Vetiver?: Special Attributes Highly resistant to pests, disease, fire etc. Tolerance of extreme climatic variations (-15 o C and 55 o C) Tolerance of prolonged drought, submergence and flood Highly tolerant to adverse soil conditions: high acidity and alkalinity, high soil salinity etc. Resistance of vetiver roots in soils is equivalent to one-sixth that of mild steel (75Mpa); more than most tree roots It s long (2.0 to 3.5 m) and massive root networks which are also very fast-growing (function able in only 4 to 6 months)

41 Application of Vetiver Disaster Mitigation: Flood Prevention and Treatment of Contaminated Water and Land

42 Application of Vetiver Road Protection Slope Protection

43 Use of Vetiver A popular drink in Bangladesh Aftershav e lotion ($115)

44 Vetiver in Bangladesh Coast Kuakata

45 LGED Project, Taras, Sirajganj A very good initiative however, we yet to discover a lot of things

46 Deforestation of mangrove Study Area: Kuakata

47 Coastal soils: Physical Properties Specific Gravity G s Natural moisture content w n (%) γ d (kn/m 3 ) Clay (%) Silt (%) Sand (%) 2.66~ ~ ~14.7 0~5 13~28 70~86 Silty sand: data of 59 samples

48 In-situ Tests at Kuakata November, 2009

49 In-situ Tests at Kuakata

50 In-situ Tests at Kuakata

51 In-situ Test Set-up Hydraulic jack 2. Wooden plate 3. Metal box ( cm 3 ) 4. Normal load 5. Metal plate 6. LVDT Schematic Diagram of the Test set-up

52 In-situ Test Set-up Block Sample Test set-up

53 Failure Pattern of Vetiver Rooted Soil Failure pattern of Soil without root Massive root system of vetiver

54 Stress-strain Behaviour Shear stress, τ (kpa) UR-1, w = 14 % VR-1, w = 15 % Failure Point 5 D = 200 mm, σ = kpa 0 n Shear strain, γ (%)

55 Strength Characteristics Peak shear stress, τ max (kpa) VR, D = 200 mm UR, D = 200 mm rooted un-rooted Normal stress, σ (kpa) n Strength of vetiver rooted soil matrix is 87% higher than that of soil without root

56 Deformation Characteristics Failure shear strain, γ f (%) VR, D = 200 mm UR, D = 200 mm rooted Normal stress, σ n (kpa) un-rooted Failure strain of vetiver rooted soil is about 770% higher than that of soil without root

57 Conclusions River bank and embankment failures happen continuously throughout Bangladesh. General reasons of embankment failures are: erosion due to rain splash, wave action and overtopping of storm surge etc. Poor maintenance practice, overturning or uprooting of trees also enhance such failures. The traditional practice for protection of embankment is to use cement concrete blocks, stone or wood revetments, geotextile and plantation, etc. These are expensive and sometimes not so effective to protect them for the designed life.

58 Conclusions Protection of embankments by bioengineering process (e.g., vetiver grass) is being used in many countries efficiently. The special attributes of vetiver grass is its longer life, strong and long finely structured root system and high tolerance of extreme climatic change. Average strength of rooted soil matrix is 78% higher than that of soil without root. Again, the failure strain of the rooted soil is 515% higher than that of the soil without root. Vetiver grass has strong and long finely structured root system which makes a heavy anchor with the soil particles. Vetiver will be effective to protect the coastal embankment against erosion, runoff, wave action, flood and cyclonic tidal surge etc.

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60 Acknowledgements o o o o o o Department of Civil Engineering, BUET, Bangladesh Japan Society of Civil Engineers, JSCE, Japan Department of Civil and Environmental Engineering, Saitama University, Japan Engr Sujat Ali, LGED, Tarash Upazilla, Sirajganj, Bangladesh Engr M. Shahidul Islam, Sonali Bank, Rajshahi, Bangladesh CARITAS, Bangladesh

61 Thank you for your attention Kuakata coast, Bangladesh