Coastal erosion along the sand barreir case study in hue vietnam

COASTALEROSIONALONGTHESANDBARRIER,CASESTUDYINHUEVIETNAM Master of Science Thesis By TRAN THANH TUNG Examination committee: Prof B Petry Ass Prof Henk Jan Verhagen If Marco Pluijm INTERNATIONAL INSTITUTE FOR INFRASTRUCTURAL, HYDRAULIC AND ENVIRONMENTAL ENGINEERING DELFT, THE NETHERLANDS MARCH, 2001 Thefindings,interpretationsandconclusionsexpressedinthisstudydonotnecessari lyreflecttheviewsoftheInternationalInstitute for Infrastructural, Hydraulic and EnvironmentalEngineering ACKNOWLEDGEMENTS With a great sense of gratitude, I would like to express my sincere thanks to lr Marco Pluijm for his available guidance, supervision and suggestion during the accomplishment of my thesis work I would like to take this opportunity to express my thanks to Ass Prof H J Verhagen and lr Mich van de Wegen for their support, valuable discussion and precious remarks I would like to express my deep appreciation and sincere thanks to Prof B Petry, chairman of examination committee, for kindly agreeing to be in the examination committee I would like to thank Royal Boskalis B.V for giving the opportunity and financing my M.Sc study at IHE, Delft Furthermore, I would like to thanks to the Hanoi Water Resources University, the Center of Estuary & Coastal Engineering of the Institute of Water Resources Research of Vietnam, the Marine Hydrometeorological Center of Hydrometeorological Services of Vietnam; the Center of Remote Sensing and GIS of the National Institute of Geology Vietnam, for their supporting in data collection and valuablediscussion Special thanks to all Vietnamese colleagues at IHE and all my friend and other who have supported me in accomplishing this thesis Without their effort and encouragement perhaps this report would be never been finished To all of them, which are mentioned above, the author is sincerely indebted Personally, I express my sincere gratitude for my beloved wife and my parent, for their understanding and patience with my absence and extending their spiritual support from distant Vietnam I may never be able to repay them, but fortunately, I have a lifetime totry Delft, March2001 Tran ThanhTung ABSTRACT The problem in coastal erosion is wide spread in areas located in the coastal environment However, in many developing countries, planning and coastal management have not gained much process due to several factors, one of which is the lack of understanding the influences in the coastal system Vietnam is no exception to this problem Located on the southeast of Asia, Vietnam has a coastline of approximately 2500 kilometers exposed to the South China Sea and Pacific Ocean The marine environment, including the coastal area, plays an important role in the economic growth of the country The importance of the coastal area is indicated by the fact that 75 percent of cities in the world with a population of 100,000 or more are located within this area However, there are many conflicts of interest in coastal area that increasing number of problems needs to be solved The most encountered problem is erosion, which occurs along the sandy barrier islands coast of Thua Thien Hue Province The study area is located at Thuan An beach, 13 km from Hue city in northeast direction, situated at the middle of 120 kilometer coastline of theProvince Before come up to a solution for erosion problems along the coasts of Thua Thien Hue province, it is essential to understand the overall morphological behaviour of coastline evolution in region Thus, the main objective of this study is to investigate the erosion mechanism, simulate the shoreline evolution; predict coastline development and propose measures for stabilizing the eroding beach in future Theresultsofthestudyshowanetlongshore transportpatternandlongshoretransport rate at each study location, which are influenced by the predominant wave direction from southeast and northwest The changes in the coastline are results of gradients in net longshoretransportdistributionineachlocation.Thesechangesarepredominantlyinfluenced by the characteristics of coastline and the migration of Thuan An inlet In addition, human interventions with the construction of groyne field at south of Noa Duan have influences these change To prevent the continuing erosion on the beaches in study area, a groyne field was proposed Some recommendations on groyne length, groyne space and their influence on the safety of structure itself and on the neighbouring coasts in future were made In accompany with the "hard" solution, the study also propose a "soft" solution to immediately create an extended beach at Noa Duan without cause any negative affects on the adjacent beach There is much more to be done in order to get a sound understanding in the morphological behaviour of Thuan An inlet and the entire coastline system It is recommend setup a 2-D morphological mathematical modelling to investigate the morphology behaviour of Thuan An inlet The possible morphological consequence in future of the inlet itself and neighbouring coasts also needs to study sufficiently This is essential in creating the needed awareness for the adoption of a good coastal management programme for Thua Thien Hue Province ACKNOWLEDGEMENT ABSTRACT TABLE OF CONTENT LIST OF FIGURES TABLE OF CONTENT i LIST OF TABLES ii iii VII ix CHAPTERI- INTRODUCTION BACKGROUND I.1 I.2 I.3 STATEMENTO F PROBLEM OBJECTIVES OF STUDY, APPROACHA NDMETHODOLOGY I.3.1 The objectivesofstudy I.3.2 ApproachandMethodology BOUNDARYO F STUDY I.4 CHAPTER II-GENERAL DESCRIPTION OFSTUDYAREA II.1.INTRODUCTION II.2 THE GENERAL DESCRIPTION OFSTUDYAREA II.2.1 Location, TopographicandGeology II.2.2 Themorphologicalconditions II.2.3 Regional ClimateandMeteorology II.3.HISTORICAL DEVELOPMENT OF TIDAL INLETANDSHORELINE 11 II.3.1 Historical development of tidalinlet 11 II.3.2 Historical development of shoreline from Hai Duong toHoaDuan 13 II.4 LAGOONS Y S T E M II.4.1 Location, topographyandmorphology 14 II.4.2 Thewaterbody 14 II.4.3 Tidalin let s 14 II.4.4 Subsystem of barriersanddunes 15 14 II.4.5 Lagoon andcoastaloceanography 15 II.5 RIVERS AND THEIRCATCHMENTA RE A 16 CHAPTER III-DATA COLLECTIONANDANALYSIS 18 III.1 INTRODUCTION 18 III.2 BACKGROUND OFREQUIREMENTD A T A 18 III.2.1 Wind andwavedata 18 III.2.2 Currents 19 III.2.3 Tide 19 III.2.4 Beach profile,t o p o g r a p h i c a l maps 19 WIND ANDWAVEDATA 20 III.3 General 20 III.3.1 Description ofdataavailable 20 III.3.2 Analysis wave data at ConCo station 22 III.3.3 CURRENT ANDTIDALDATA 24 III.4 III.4.1 The tide andtidalcurrent 24 III.4.2 Windd ri ve n current 25 III.5 TOPOGRAPHICAL MAPS ANDBATHYMETRYD A T A 26 III.6 SEDIMENT CHARACTERISTIC 26 28 CHAPTER IV -COASTALMORPHOLOGY IV.1 SEDIMENTTR A N S P O RT IV.1.1 28 General 28 IV.1.1.1 Longshore transport andlongshorecurrents 28 IV.1.1.2 Onshore-offshoretransport 29 IV.1.2 Basic aspectaboutmodeling 29 IV.1.2.1 ObjectiveofModelling 29 IV.1.2.2 Brief description ofUNIBESTmodel 30 IV.2 COMPUTATION LONGSHORESEDIMENTTRANSPORT 32 Input Data and Some Assumption orC o n s i d e r a t i o n N e e d s IV.2.1 32 IV.2.1.1 TheW a v e s Climate 32 IV.2.1.2 TheBeachProfile 33 IV.2.1.3 The coefficients for the energyd e c a y calculation 34 IV.2.1.4 The coefficients fortransportformula 34 IV.2.1.5 The assumption of straight coast and paralleld e p t h contour 34 IV.2.2 The Main Model from Thuan An to ChanM a y Bay 35 IV.2.2.1 The objectives ofmainmodel 35 IV.2.2.2 CoastOrientationAngles 35 IV.2.2.3 Select the sedimenttransportformula 36 IV.2.2.4 Set-up a Coastline Model from Thuan An inlet to ChanMayBay 37 IV.2.2.5 Simulate theshorelinedevelopment 38 IV.2.2.6 Conclusion 41 IV.3 SIMULATE THE EVOLUTION OF SHORELINE FROM THUAN AN TOHOADUAN 41 IV.3.1 Introduction 41 IV.3.2 Setup the coastline model from Thuan An toHoaDuan 42 IV.3.3 Coastline Change Based on theTopographicalMaps 43 IV.3.4 Calibration of thecoastlinemodel 44 IV.3.4.1 The sensitivity oftransportcoefficients 45 IV.3.4.2 Sensitivity ofboundaryconditions 46 IV.3.5 Simulation of the influence of Hoa Duan gap after closure on shoreline evolution of adjacentbeaches 48 IV.3.5.1 Set-up of theCoastlineModel 48 IV.3.5.2 ResultsandDiscussion 49 IV.3.6 Simulation the shoreline evolution with groynes field atHoaDuan 50 IV.3.6.1 Set-up thecoastlinemodel 51 IV.3.6.2 Discussion 53 IV.4 THE INFLUENCE OF THE TIDAL INLETS IN THE STUDYAREA IV.4.1 The Morphology ofT i d a l Inlet 54 IV.4.1.1 Hydrodynamic classification oftidalinlets 54 IV.4.1.2 By-passing oftidalinlet 56