Doctoral Dissertation ESTIMATION OF EROSION RESISTANCE OF COHESIVE BANK IN RIVER AND AROUND RIVER MOUTH （粘性土で構成された河川堤防及び河口周辺護岸 の侵食耐性の評価に関する研究） BUI TRONG VINH Department of Civil Engineering Graduate School of Engineering Osaka University August, 2009 Doctoral Dissertation ESTIMATION OF EROSION RESISTANCE OF COHESIVE BANK IN RIVER AND AROUND RIVER MOUTH （粘性土で構成された河川堤防及び河口周辺護 岸の侵食耐性の評価に関する研究） A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Civil Engineering by Bui Trong Vinh Supervised by Prof Ichiro Deguchi Graduate School of Engineering Osaka University, Japan August, 2009 ACKNOWLEDGEMENT This dissertation has been carried out under the academic advice of Prof Ichiro Deguchi at Department of Civil Engineering, Osaka University I would like to express my deep gratefulness to him, my great supervisor, who always encourages and supports me during my study and living in Japan I owe special thanks to Associate Prof Susumu Araki, who taught me how to solve problems when I met and what the hard work we face in life I would like to gratefully acknowledge Prof Keiji Nakatsuji who taught me and questioned with his excellent mind I had some good chance to go with him for taking part in some workshops, seminars in Japan, Vietnam, and Korea He also always helps and supports me during my study His excellent critics help me understand the important effects of tide in my study I thank Prof Shuzo Nishida who gave me important advice when we joined the General Seminar of Core Program in Danang City and during the journey in Vietnam His critics helped me have some new view points about both scientific meanings and real applications of my study I also thank Prof Yasutsugu Nitta for his evaluation on my dissertation defense I am greatly indebted to Prof Huynh Thi Minh Hang who was my supervisor when I was undergraduate and master student in Vietnam Now she passed away, but in my mind, she is still there I thank Assistant Prof Mamoru Arita, who helped me when I got troubles with experimental device I appreciate his enthusiasm during the time at conferences and field investigation in Japan, Portugal, Korea and Vietnam I also had a very beautiful time when I studied with and met many Japanese students belonged to Prof Deguchi Lab Now they are working in many companies, but during the study, I learned very much from them I am sorry because I not remember the name of all students, but special thanks to Mr Nakaue, Mr Shimizu, Mr Nomura, Mr Sabusaki, Ms Fukuhara, Ms Yoshiyama etc I thank Mr Han James for his help to prepare the artificial bank and bed of the flume experiments and to take photos during the field investigation I also thank Prof Fujita, Prof Ike, Prof Viet and his staffs, JSPS, and Monbusho who supported me the finance during my stay and my study in Core University Program and PhD Program I am also grateful to the faculty staffs at Department of Civil Engineering, Affair Department of International Students for their kindness Last but not least, I would like to thank my family, friends, and colleagues of Faculty of Geological and Petroleum Engineering – Hochiminh City University of Technology – VNU-HCMC who always support and help me during the time I’ve been living and studying in Vietnam and in Japan i List of Publications [1] Bui Trong Vinh, Ichiro Deguchi, Mamoru Arita, 2009 “Erosion Mechanisms of Cohesive Bed and Bank Materials” Proceedings of the Annual International Offshore and Polar Engineering Conference & Exhibition (ISOPE) Osaka, Japan, June 21-26, 2009, Vol III, pp 1305-1312 [2] Bui Trong Vinh, Ichiro Deguchi, Keiji Nakatsuji, 2008 “Beach Erosion Caused by Development in Littoral Region – Effect of Sand Extraction around River Mouth” Proceedings of the 8th General Seminar on Environmental Science & Technology Issues Japan, Osaka, Nov 2008, pp 114-119 [3] Bui Trong Vinh, Deguchi Ichiro, Arita Mamoru, Fukuhara Saori, 2008 “Experimental Study on Critical Shear Stress of Cohesive Bed Material for Erosion” Annual Journal of Coastal Engineering, JSCE, 2008, Vol.1, pp 531-535 (in Japanese) [4] Bui Trong Vinh, Ichiro Deguchi, Mamoru Arita, Susumu Araki, 2008 “Measurement of Critical Shear Stress for Erosion of Cohesive Riverbanks” The International Conference on Marine Science and Technology - OCEANS'08 Japan, Kobe, April 8, 2008 (in CD-Rom) [5] B.T Vinh, I Deguchi, S Araki, T Nakaue, A Shimizu, 2007 “The Mechanism of Beach Erosion in Southern Part of Red River Delta, Vietnam” Proceedings of the Annual International Offshore and Polar Engineering Conference & Exhibition (ISOPE) Lisbon, Portugal, July 1-6, 2007, Vol III, pp 2461-2466 [6] I Deguchi, S Araki, T Nakaue, B.T Vinh, 2006 “Monitoring of the Change in Coastal Environment in Southern Part of Red River Delta from Satellite Images and the Mechanism of Beach Erosion” Proceedings of the 6th General Seminar on Environmental Science & Technology Issues Japan, Kumamoto, Oct 2006、pp 144-152 ii CONTENTS Acknowledgement List of Publications Contents List of Tables List of Figures i ii iii v vi Chapter Introduction 1.1 1.2 1.3 1.4 Background Objectives of the Study The Study Areas Outline of the Dissertation References Chapter Effects of Development around River Mouth and Shallow Water Region in the Sea 2.1 2.2 2.3 2.4 Introduction Detection of Shoreline Retreat from Satellite Images and Analysis of the Erosion Mechanism Caused by the Development of Mangrove Forests 2.2.1 Sites of investigation 2.2.2 Materials and methods 2.2.3 Results of analyzing satellite data 2.2.4 The erosion mechanism of beaches in Site-A and Site-B 2.2.5 Numerical model Effects of Sand Extraction on Beach Erosion Conclusions References Chapter Experimental Study on Critical Shear Stress of Cohesive Bed Material for Erosion 3.1 3.2 3.3 3.4 Introduction Experimental Apparatus and Procedures 3.2.1 Non-vertical jet test apparatus 3.2.2 Procedures for determining the τc and kd Experimental Study on Remolded Samples 3.3.1 Remolded samples making process 3.3.2 Procedures for determining the τc and kd of remolded samples In Situ Experiments 3.4.1 Experimental sites 3.4.2 Temperature iii 2 6 7 11 15 19 22 24 24 26 26 26 26 27 30 30 33 34 34 35 3.4.3 3.4.4 3.4.5 3.4.6 3.4.7 3.5 3.6 Rainfall Tidal currents and waves Vegetation and aquatic animals The properties of cohesive soils of Soairap river banks Procedures for measuring the τc and kd of undisturbed samples Results and Discussions Conclusions References Chapter Estimation of Erosion Resistance of Cohesive Bank in River and around River Mouth 4.1 4.2 4.3 4.4 4.5 4.6 4.7 Introduction Flume Experiments 4.2.1 Experimental apparatus 4.2.2 Results and discussions Wave Basin Experiments 4.3.1 Experimental apparatus 4.3.2 Results and discussions 4.3.2.1 Erosion caused by waves (Case-1 to Case-3) 4.3.2.2 Erosion profiles caused by waves, wave-opposing currents, and wave-following currents Numerical Model 4.4.1 Governing equations 4.4.2 Estimation of applied shear stress around river mouth 4.4.2.1 Boundary conditions 4.4.2.2 Simulation results and applicability of the model 4.4.3 Estimation of applied shear stress on cohesive bank in river 4.4.3.1 Boundary conditions 4.4.3.2 Simulation results and discussions Estimation of Erosion Resistance along Soairap River 4.5.1 Field investigation and scour test 4.5.2 Estimation of erosion resistance along Soairap River Discussions Conclusions References Chapter Conclusions 36 36 38 39 40 41 44 44 46 46 47 47 48 50 50 52 52 54 57 57 59 59 60 68 69 71 75 75 77 79 80 80 82 iv List of Tables Chapter Effects of Development around River Mouth and Shallow Water Region in the Sea Table 2.1 Satellite data used for the study Chapter Experimental Study on Critical Shear Stress of Cohesive Bed Material for Erosion Table 3.1 Table 3.2 Table 3.3 Table 3.4 Table 3.5 Table 3.6 Table 3.7 Table 3.8 Table 3.9 Table 3.10 Table 3.11 Remolded samples with only sand and clay Remolded samples with 40% of silt Remolded samples with 10% sand Remolded samples with the change of moisture content Samples with only sand-clay content and moisture content Remolded samples with the change of salinity Remolded samples with the change of consolidation time Remolded samples with the change of dead root and leaves Properties of cohesive soils of Soairap river banks The results of experiments on effect of consolidation The results of experiments on effect of dead roots and leaves 31 31 31 32 32 32 32 33 39 43 43 Chapter Estimation of Erosion Resistance of Cohesive Bank in River and around River Mouth Table 4.1 Table 4.2 Table 4.3 Table 4.4 Table 4.5 Table 4.6 Table 4.7 Table 4.8 Table 4.9 Erosion properties of remolded samples in the flume test Experimental conditions in the basin tests Erosion properties of remolded samples in the basin tests Input conditions of laboratory scale model Calculation results around river mouth Input conditions of the model to investigate the effect of waves and wave-induced currents Input conditions of the model to investigate the effect of river flows Input conditions of the model to investigate the effect of waves, wave-induced currents and tidal currents Input conditions of the model to investigate the effect of waves with weak currents v 48 52 52 60 61 69 70 70 70 List of Figures Chapter Introduction Fig 1.1 Location of study areas Chapter Effects of Development around River Mouth and Shallow Water Region in the Sea Fig 2.1 Fig 2.2 Fig 2.3 Fig 2.4 Fig 2.5 Fig 2.6 Fig 2.7 Fig 2.8 Fig 2.9 Fig 2.10 Fig 2.11 Fig 2.12 Fig 2.13 Fig 2.14 Fig 2.15 Fig 2.16 Fig 2.17 Fig 2.18 Fig 2.19 Fig 2.20 Fig 2.21 Fig 2.22 Fig 2.23 Fig 2.24 Fig 2.25 Fig 2.26 Fig 2.27 Fig 2.28 Fig 2.29 Beach erosion around fish harbor Beach erosion by sand extraction Location of study areas Location of Site-A (Landsat/TM-1989, May 29) Location of Site-B (Landsat/TM-1989, May 29) NDVI image of Site-A TM5-2 image of northern Site-B Band-4 images of Landsat/TM in Site-A Shoreline changes around Huasai, Site-A (1992, 1996, and 1998) Comparison of land-use in Sept 1998 and Sept 2001 The shoreline change near Balat river mouth The shoreline change near Ninhco River The shoreline change in Haihau district The shoreline change in Vanly area The shoreline change in Giaothuy district Expected topography change around the shrimp pond Beach erosion caused by remained abandoned shrimp ponds (near Huasai, Thailand - Site-A) Beach erosion caused by remained abandoned shrimp ponds (in Haihau district, northern Vietnam - Site-B) The erosion process in front of the double sea dike system (in Haihau district, northern Vietnam - Site-B) The mechanism of longshore sediment transport in summer (without mangrove forest) The mechanism of longshore sediment transport in winter (without mangrove forest) The mechanism of longshore sediment transport in winter (with thick mangrove forest) Boundary conditions (B.C.) in summer Boundary conditions (B.C.) in winter Calculated shoreline change without mangrove forest Calculated shoreline change with mangrove forest Calculated shoreline retreat backed by sea dike Sand extraction sites and erosion place in Kochi coast, Japan Bottom topography around river mouth of Niyodo River, Kochi Coast, Japan vi 9 10 10 11 12 13 13 14 14 15 15 16 16 17 17 18 18 18 20 20 21 21 22 22 23 Chapter Experimental Study on Critical Shear Stress of Cohesive Bed Material for Erosion Fig 3.1 Fig 3.2 Fig 3.3 Fig 3.4 Fig 3.5 Fig 3.6 Fig 3.7 Fig 3.8 Fig 3.9 Fig 3.10 Fig 3.11 Fig 3.12 Fig 3.13 Fig 3.14 Fig 3.15 Fig 3.16 Fig 3.17 Fig 3.18 Fig 3.19 Fig 3.20 Fig 3.21 Fig 3.22 Fig 3.23 Fig 3.24 Fig 3.25 Fig 3.26 Non-vertical submerged jet test apparatus Diffusion principles (a) and stress distribution (b) Calibration of the initial jet velocity at nozzle Remolded sample after mixing (a) and after pouring water (b) Remolded sample before testing Mixing rates and moisture content of remolded samples Procedure for determining the τc Procedure for determining the kd Study area and measuring sites In situ submerged jet test device Compact-WH (a) and Compact-EM (b) Average air temperature from 2002 to 2005 (Tan Son Hoa Station) Annual rainfall from 2002 to 2005 (Tan Son Hoa Station) The water level from 2002 to 2005 (Phu An Station) Wave data measured at site SR2R Tidal current data measured at site SR2R Wave data measured at site SR6L Tidal current data measured at site SR6L Exposed roots and burrowed holes at SR5R Physical properties of measuring site samples Procedure for determining the τc at SR5R Procedure for determining the kd at SR5R Relationship between the τc and clay content Relationship between the τc and moisture content Relationship between the τc and salinity Relationship between the kd and τc 27 28 29 30 30 33 34 34 35 35 35 35 36 36 37 37 38 38 39 39 40 40 41 42 42 43 Chapter Estimation of Erosion Resistance of Cohesive Bank in River and around River Mouth Fig 4.1 Fig 4.2 Fig 4.3 Fig 4.4 Fig 4.5 Fig 4.6 Fig 4.7 Fig 4.8 Fig 4.9 Fig 4.10 Fig 4.11 Fig 4.12 Fig 4.13 Fig 4.14 Fig 4.15 Sketch of test cross section of the flume Velocity profile in the center of test section Erosion of remolded sample of (P1) after 2-hour testing Erosion of remolded bank sample after 18-hour testing Sketch of wave-river basin and river mouth model Erosion caused by waves after 3-hour testing Wave data of the experiment with wave-opposing currents Erosion profile in Case-4 and Case-5 Wave data at the starting time of the experiment with wave-following currents Erosion profiles in Case-6 and Case-7 The domain of laboratory scale model Distribution of current velocities (Case-3) Distribution of wave heights (Case-3) Distribution of applied shear stresses (Case-3) Distribution of current velocities (Case-6) vii 47 48 49 50 51 53 54 55 56 56 60 62 62 62 63 Fig 4.16 Fig 4.17 Fig 4.18 Fig 4.19 Fig 4.20 Fig 4.21 Fig 4.22 Fig 4.23 Fig 4.24 Fig 4.25 Fig 4.26 Fig 4.27 Fig 4.28 Fig 4.29 Fig 4.30 Fig 4.31 Fig 4.32 Distribution of wave heights (Case-6) Distribution of applied shear stresses (Case-6) Distribution of current velocities (Case-8) Distribution of wave heights (Case-8) Distribution of applied shear stresses (Case-8) Distribution of current velocities (Case-11) Distribution of wave heights (Case-11) Distribution of applied shear stresses (Case-11) Effect of waves and river discharge on applied shear stresses The domain of field scale model Effect of only waves and wave-induced currents on shear stresses Effect of river flow and tidal range on applied shear stresses Effect of waves and wave-following currents on shear stresses Effect of waves and wave-opposing currents on shear stresses Study sites in Soairap River Erosion site 21R of Soairap river bank in 2007 (a) and in 2008 (b) Distribution of shear velocities in condition with only currents (a), only waves (b), and waves-currents (c) viii 63 64 65 65 65 66 66 67 68 69 72 73 74 75 76 77 78