estimation of erosion resistance of cohesive bank in river and around river mouth

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 i 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 do 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. ii 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 8 th 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 6 th General Seminar on Environmental Science & Technology Issues. Japan, Kumamoto, Oct. 2006、pp. 144-152. iii CONTENTS Acknowledgement i List of Publications ii Contents iii List of Tables v List of Figures vi Chapter 1 Introduction 1 1.1 Background 1 1.2 Objectives of the Study 2 1.3 The Study Areas 2 1.4 Outline of the Dissertation 3 References 4 Chapter 2 Effects of Development around River Mouth and Shallow Water Region in the Sea 6 2.1 Introduction 6 2.2 Detection of Shoreline Retreat from Satellite Images and Analysis of the Erosion Mechanism Caused by the Development of Mangrove Forests 7 2.2.1 Sites of investigation 7 2.2.2 Materials and methods 8 2.2.3 Results of analyzing satellite data 11 2.2.4 The erosion mechanism of beaches in Site-A and Site-B 15 2.2.5 Numerical model 19 2.3 Effects of Sand Extraction on Beach Erosion 22 2.4 Conclusions 24 References 24 Chapter 3 Experimental Study on Critical Shear Stress of Cohesive Bed Material for Erosion 26 3.1 Introduction 26 3.2 Experimental Apparatus and Procedures 26 3.2.1 Non-vertical jet test apparatus 26 3.2.2 Procedures for determining the τ c and k d 27 3.3 Experimental Study on Remolded Samples 30 3.3.1 Remolded samples making process 30 3.3.2 Procedures for determining the τ c and k d of remolded samples 33 3.4 In Situ Experiments 34 3.4.1 Experimental sites 34 3.4.2 Temperature 35 iv 3.4.3 Rainfall 36 3.4.4 Tidal currents and waves 36 3.4.5 Vegetation and aquatic animals 38 3.4.6 The properties of cohesive soils of Soairap river banks 39 3.4.7 Procedures for measuring the τ c and k d of undisturbed samples 40 3.5 Results and Discussions 41 3.6 Conclusions 44 References 44 Chapter 4 Estimation of Erosion Resistance of Cohesive Bank in River and around River Mouth 46 4.1 Introduction 46 4.2 Flume Experiments 47 4.2.1 Experimental apparatus 47 4.2.2 Results and discussions 48 4.3 Wave Basin Experiments 50 4.3.1 Experimental apparatus 50 4.3.2 Results and discussions 52 4.3.2.1 Erosion caused by waves (Case-1 to Case-3) 52 4.3.2.2 Erosion profiles caused by waves, wave-opposing currents, and wave-following currents 54 4.4 Numerical Model 57 4.4.1 Governing equations 57 4.4.2 Estimation of applied shear stress around river mouth 59 4.4.2.1 Boundary conditions 59 4.4.2.2 Simulation results and applicability of the model 60 4.4.3 Estimation of applied shear stress on cohesive bank in river 68 4.4.3.1 Boundary conditions 69 4.4.3.2 Simulation results and discussions 71 4.5 Estimation of Erosion Resistance along Soairap River 75 4.5.1 Field investigation and scour test 75 4.5.2 Estimation of erosion resistance along Soairap River 77 4.6 Discussions 79 4.7 Conclusions 80 References 80 Chapter 5 Conclusions 82 v List of Tables Chapter 2 Effects of Development around River Mouth and Shallow Water Region in the Sea Table 2.1 Satellite data used for the study 9 Chapter 3 Experimental Study on Critical Shear Stress of Cohesive Bed Material for Erosion Table 3.1 Remolded samples with only sand and clay 31 Table 3.2 Remolded samples with 40% of silt 31 Table 3.3 Remolded samples with 10% sand 31 Table 3.4 Remolded samples with the change of moisture content 32 Table 3.5 Samples with only sand-clay content and moisture content 32 Table 3.6 Remolded samples with the change of salinity 32 Table 3.7 Remolded samples with the change of consolidation time 32 Table 3.8 Remolded samples with the change of dead root and leaves 33 Table 3.9 Properties of cohesive soils of Soairap river banks 39 Table 3.10 The results of experiments on effect of consolidation 43 Table 3.11 The results of experiments on effect of dead roots and leaves 43 Chapter 4 Estimation of Erosion Resistance of Cohesive Bank in River and around River Mouth Table 4.1 Erosion properties of remolded samples in the flume test 48 Table 4.2 Experimental conditions in the basin tests 52 Table 4.3 Erosion properties of remolded samples in the basin tests 52 Table 4.4 Input conditions of laboratory scale model 60 Table 4.5 Calculation results around river mouth 61 Table 4.6 Input conditions of the model to investigate the effect of waves and wave-induced currents 69 Table 4.7 Input conditions of the model to investigate the effect of river flows 70 Table 4.8 Input conditions of the model to investigate the effect of waves, wave-induced currents and tidal currents 70 Table 4.9 Input conditions of the model to investigate the effect of waves with weak currents 70 vi List of Figures Chapter 1 Introduction Fig. 1.1 Location of study areas 3 Chapter 2 Effects of Development around River Mouth and Shallow Water Region in the Sea Fig. 2.1 Beach erosion around fish harbor 6 Fig. 2.2 Beach erosion by sand extraction 7 Fig. 2.3 Location of study areas 8 Fig. 2.4 Location of Site-A (Landsat/TM-1989, May 29) 9 Fig. 2.5 Location of Site-B (Landsat/TM-1989, May 29) 9 Fig. 2.6 NDVI image of Site-A 10 Fig. 2.7 TM 5-2 image of northern Site-B 10 Fig. 2.8 Band-4 images of Landsat/TM in Site-A 11 Fig. 2.9 Shoreline changes around Huasai, Site-A (1992, 1996, and 1998) 12 Fig. 2.10 Comparison of land-use in Sept. 1998 and Sept. 2001 13 Fig. 2.11 The shoreline change near Balat river mouth 13 Fig. 2.12 The shoreline change near Ninhco River 14 Fig. 2.13 The shoreline change in Haihau district 14 Fig. 2.14 The shoreline change in Vanly area 15 Fig. 2.15 The shoreline change in Giaothuy district 15 Fig. 2.16 Expected topography change around the shrimp pond 16 Fig. 2.17 Beach erosion caused by remained abandoned shrimp ponds (near Huasai, Thailand - Site-A) 16 Fig. 2.18 Beach erosion caused by remained abandoned shrimp ponds (in Haihau district, northern Vietnam - Site-B) 17 Fig. 2.19 The erosion process in front of the double sea dike system (in Haihau district, northern Vietnam - Site-B) 17 Fig. 2.20 The mechanism of longshore sediment transport in summer (without mangrove forest) 18 Fig. 2.21 The mechanism of longshore sediment transport in winter (without mangrove forest) 18 Fig. 2.22 The mechanism of longshore sediment transport in winter (with thick mangrove forest) 18 Fig. 2.23 Boundary conditions (B.C.) in summer 20 Fig. 2.24 Boundary conditions (B.C.) in winter 20 Fig. 2.25 Calculated shoreline change without mangrove forest 21 Fig. 2.26 Calculated shoreline change with mangrove forest 21 Fig. 2.27 Calculated shoreline retreat backed by sea dike 22 Fig. 2.28 Sand extraction sites and erosion place in Kochi coast, Japan 22 Fig. 2.29 Bottom topography around river mouth of Niyodo River, Kochi Coast, Japan 23 vii Chapter 3 Experimental Study on Critical Shear Stress of Cohesive Bed Material for Erosion Fig. 3.1 Non-vertical submerged jet test apparatus 27 Fig. 3.2 Diffusion principles (a) and stress distribution (b) 28 Fig. 3.3 Calibration of the initial jet velocity at nozzle 29 Fig. 3.4 Remolded sample after mixing (a) and after pouring water (b) 30 Fig. 3.5 Remolded sample before testing 30 Fig. 3.6 Mixing rates and moisture content of remolded samples 33 Fig. 3.7 Procedure for determining the τ c 34 Fig. 3.8 Procedure for determining the k d 34 Fig. 3.9 Study area and measuring sites 35 Fig. 3.10 In situ submerged jet test device 35 Fig. 3.11 Compact-WH (a) and Compact-EM (b) 35 Fig. 3.12 Average air temperature from 2002 to 2005 (Tan Son Hoa Station) 35 Fig. 3.13 Annual rainfall from 2002 to 2005 (Tan Son Hoa Station) 36 Fig. 3.14 The water level from 2002 to 2005 (Phu An Station) 36 Fig. 3.15 Wave data measured at site SR2R 37 Fig. 3.16 Tidal current data measured at site SR2R 37 Fig. 3.17 Wave data measured at site SR6L 38 Fig. 3.18 Tidal current data measured at site SR6L 38 Fig. 3.19 Exposed roots and burrowed holes at SR5R 39 Fig. 3.20 Physical properties of measuring site samples 39 Fig. 3.21 Procedure for determining the τ c at SR5R 40 Fig. 3.22 Procedure for determining the k d at SR5R 40 Fig. 3.23 Relationship between the τ c and clay content 41 Fig. 3.24 Relationship between the τ c and moisture content 42 Fig. 3.25 Relationship between the τ c and salinity 42 Fig. 3.26 Relationship between the k d and τ c 43 Chapter 4 Estimation of Erosion Resistance of Cohesive Bank in River and around River Mouth Fig. 4.1 Sketch of test cross section of the flume 47 Fig. 4.2 Velocity profile in the center of test section 48 Fig. 4.3 Erosion of remolded sample of (P1) after 2-hour testing 49 Fig. 4.4 Erosion of remolded bank sample after 18-hour testing 50 Fig. 4.5 Sketch of wave-river basin and river mouth model 51 Fig. 4.6 Erosion caused by waves after 3-hour testing 53 Fig. 4.7 Wave data of the experiment with wave-opposing currents 54 Fig. 4.8 Erosion profile in Case-4 and Case-5 55 Fig. 4.9 Wave data at the starting time of the experiment with wave-following currents 56 Fig. 4.10 Erosion profiles in Case-6 and Case-7 56 Fig. 4.11 The domain of laboratory scale model 60 Fig. 4.12 Distribution of current velocities (Case-3) 62 Fig. 4.13 Distribution of wave heights (Case-3) 62 Fig. 4.14 Distribution of applied shear stresses (Case-3) 62 Fig. 4.15 Distribution of current velocities (Case-6) 63 viii Fig. 4.16 Distribution of wave heights (Case-6) 63 Fig. 4.17 Distribution of applied shear stresses (Case-6) 64 Fig. 4.18 Distribution of current velocities (Case-8) 65 Fig. 4.19 Distribution of wave heights (Case-8) 65 Fig. 4.20 Distribution of applied shear stresses (Case-8) 65 Fig. 4.21 Distribution of current velocities (Case-11) 66 Fig. 4.22 Distribution of wave heights (Case-11) 66 Fig. 4.23 Distribution of applied shear stresses (Case-11) 67 Fig. 4.24 Effect of waves and river discharge on applied shear stresses 68 Fig. 4.25 The domain of field scale model 69 Fig. 4.26 Effect of only waves and wave-induced currents on shear stresses 72 Fig. 4.27 Effect of river flow and tidal range on applied shear stresses 73 Fig. 4.28 Effect of waves and wave-following currents on shear stresses 74 Fig. 4.29 Effect of waves and wave-opposing currents on shear stresses 75 Fig. 4.30 Study sites in Soairap River 76 Fig. 4.31 Erosion site 21R of Soairap river bank in 2007 (a) and in 2008 (b) 77 Fig. 4.32 Distribution of shear velocities in condition with only currents (a), only waves (b), and waves-currents (c) 78 [...]... and erosion resistance of cohesive bed, bank and shore [4] are investigated Various kinds of remodeled samples of cohesive bed material were made and examined in 2-D flume with unidirectional currents and 3-D wave basin under the action of waves and currents The property of erosion resistance is investigated by using numerical models to calculate the erosion rates of artificial and real bed, bank and. .. procedure for detecting water line from satellite images to evaluate the amount of erosion in two coasts in Thailand and Vietnam and investigates the mechanism of erosion Then the author investigates the effects of sand extraction on beach erosion using the fund of information of the bottom topography around the river mouth of Niyodo River in the Shikoku Island 2.2 Detection of Shoreline Retreat from... evaluating critical shear stress of cohesive soils for erosion (3) Study on erosion mechanism of cohesive bed, bank and shore and propose procedure for examining erosion resistance 1.3 The Study Areas The study areas consist of Vietnam, Thailand, and Japan In Vietnam, two main parts of southern coast of the Red River Delta and coastal region around Soairap river mouth (southern Vietnam) were concerned In. .. understand because of the nature of cohesive materials in cohesive banks The erosion processes in cohesive banks are distinctly different from those of non -cohesive ones because of the irreversible processes In the river mouth, estuaries, and newly developed coastal regions, there are several physical factors acting on the banks, bed and shores that can influence erosion rates including wind waves, ship... Shoreline changes around Huasai, Site-A (1992, 1996, and 1998) Detected change in land-cover and the location of shoreline around river mouth of Site-B Figure 2.10 illustrates the classification of land-cover in Sept 1998 and Sept 2001 obtained using supervised classification From this figure, it is found that the area of mangrove forest coloring red increased rapidly in both sides of the river mouth. .. and two large river mouths named Ninhco and Balat river mouths (Fig 2.5) In front of the dikes, the beach slope is very gentle and varies along the coastline from 1:40 on eroding beaches to 1:200 in other places [15] The beaches consist of very fine sand with an average grain size of about 0.08 mm In Balat river mouth, there is a thick mangrove forest advancing offshore In 2005, Typhoon 7 (international... Thailand and Vietnam were introduced The erosion mechanism of beaches in both southern coast of Thailand and southern coast of Red River Delta (Vietnam) could be understood by analyzing satellite images The NDVI and TM5-2 images were used to extract the changes of shorelines and land-use in these regions effectively By comparing the detected location of the shorelines for past 30 years, two kinds of erosion. .. Erosion place from 1974 to 1997 Pacific Ocean Fig 2.28 Sand extraction sites and erosion place in Kochi coast, Japan 22 Figure 2.29 shows bottom topography in front of the Niyodo river mouth from 1974 to 1997 From 1974 to 1988, total volume of extracted sand was more than 4.6 million cubic meters in front of Niyodo river mouth There was a clear river mouth terrace in front of the opening of river mouth. .. investigate the erosion mechanism of cohesive bank in river and around river mouth to evaluate erosion resistance of cohesive soil and to establish the procedure for stabilizing and utilizing the coastal regions effectively To achieve the aim, three research objectives have been carried out as following (1) Assess the effects of development, preservation and disaster prevention on coastal erosion in some Asian... the extraction of sand was the cause of shoreline retreat with annual rate of 8.1 m/year The effect of excessive sand extraction around Niyodo river mouth has been lasting long River mouth terrace Extracted hollow 1974 1981 1984 1988 1992 1997 1000m Fig 2.29 Bottom topography around river mouth of Niyodo River, Kochi Coast, Japan 23 2.4 Conclusions In the present study, erosion of beaches in some Asian . investigate the erosion mechanism of cohesive bank in river and around river mouth to evaluate erosion resistance of cohesive soil and to establish the procedure for stabilizing and utilizing. Chapter 4 Estimation of Erosion Resistance of Cohesive Bank in River and around River Mouth Fig. 4.1 Sketch of test cross section of the flume 47 Fig. 4.2 Velocity profile in the center of test. Gulf of Thailand Balat river mouth Ninhco river mouth Site-B Namdinh 10 25 25 25 BandBand BandBand TM + − = − In both sites, Landsat data were used to investigate the change in the land-use