MINISTRY OF EDUCATION AND TRAINING MINISTRY OF AGRICULTURE AND RURAL DEVELOPMENT IMPACTS OF THE VUNG TAU — GO CONG SEA DYKE ON HYDRODYNAMIC FLOW REGIME BUI DUC TOAN MSc Thesis on Integrated Water Resources Management August 2015 BUI DUC TOAN IMPACTS OF THE VUNG TAU - GO CONG SEA DYKE ON HYDRODYNAMIC FLOW REGIME Major: Integrated Water Resources Management OF MASTER DEGREE, Supervisor (9): Assoc. Nguyen Cao Don This research is done for the partial fulfilment of requirement for laster of Science Degree at Thuy Loi University (This Master Programme is supported by NICHE ~ VNM 106 Project) Ha Noi, August, 2015 ABSTRACT The low-lying terrain downstream of Saigon - Dong Nai River is most affected by natural disasters such as, flooding, saltwater intrusion causing difficulties in process of socio-economic development, The project of building Vung Tau - Go Cong sea dyke with a length of 32km was proposed to solve these problems, in particularly creating a reservoir for storing water and preventing saltwater intrusion, expanding urban space, industrial parks, tourism, services shelter from the storm boats, reserving fresh water in the future, However, hydrodynamic regime in this area would be altered by the construction of Vung Tau - Go Cong, causing sedimentation in estuaries, changing salt marsh ecosystems. The comparison between hydrodynamic regime with two scenatios before and after construction sea dyke will be mentioned in this thesis, In this study, MIKE 21 model was used to simulate hydrodynamic regime in study area, The computed domain is described as follow: Latitude: 1080000 ~ 1160000; Longtitude: 67000-70000. The grid which used in computation was unstructured mesh because it met the requirement of accuracy and detail computation.
Exported data from MIKE 11 model was used as input data for discharge boundary of model. The observed water level data of Vung Tau station and global tide prediction data were used for model libration and validation, Duration time of model calibration and validation. for the research site from 17/October/2000 to 20/10/2000 and 21/Oetober/2000 to 24/10/2000 respectively. The calibrated parameter was bed resistance.
The application of model is considered in two scenarios: without sea dike and with sea dike. Both scenari how semidiumal tide regime in Go Cong- Vung Tau area, Moreover those confirm that current is mainly influenced by tide and flow of estuaries in coastal area. The construction of sea dike creats two distinct areas: Thefi L area- Res voir including main dike, branch dike and Soai Rap estuary; The second area - Ganh Rai Bay containing Long Tau, Thi Vai estuaries and branch dike, There is a significant change in hydrodynamic regime between two scenarios at inside reservoir, for example considerable differences in phase, fluctuation amplitude of water level/current. Except for inside the reservoir, there is a small change in phase, fluctuation amplitude of water level/current at outside Thereby certify that the work presented in this thesis entitled, “Impacts of the Dung Tau ~ Go Cong sea dyke on hydrodynamic flow regime ” in partial fulfillment of the requirement for the award of the Master of Science in Integrated Water Resource Management, is done by myselft under the supervision of Assoc.
Nguyen Cao Don, The matter embodied in this thesis has not been submitted by me for the award of any other degree or diploma, Ha Noi, date August 2015 Bui Due Toan ACKNOWLEDGEMENTS First and foremost I would like to thank the supervisor Assoc. PhD Nguyen Cao Don for his great contribution in this thesis, for supporting me and guiding me stay on the right trend, I want to show deep thanks to Assoc. Nguyen Thu Hien and Dr. Hoang Nguyet Minh who are main co- ordinators, making value contributions to success in Master course and I would like to thank the CoMEM Mariette who help me improve English writing skill, [ would like to thank my wife, my family and my colleagues for their continuous encourages.
1 would like to express deep thanks to KC.16/11-15 state project namely “Research, identification scientific arguments and proposal of Phu Quốc — Con Dao marine spatial planning for sustainable development” (Assoc. Pham Quy Nhan is the Project Manager) that I am joining to because ofits funding Finally I would like to thank NICHE VNM-106 project (funded by NUFFIC) for finance supporting and facilities for studying process. Ha Noi, date August 2015 Bui Duc Toan TABLE OF CONTENT ABSTRACT DECLARATION ACKNOWLEDGEMENTS.3 Objectives and Research questions.4 Methods: 15 Structure of the thesis CHAPTER 2: LITERATURE REVIEW 2.1 The studies on Mekong Delta of foreign authors 18 2.2 The related researches on the lower downstream of Sai Gon-Dong Nai river basin 20 2.3 Overview of hvdrodynamic models 23 2.4 Overview of MIKE 21 27 CHAPTER 3: ANALYSIS IMPACTS OF THE VUNG TAU - GO CONG SEA DYKE ON HYDRODYNAMIC REGIME, 29 3.4 Water level boundaries 39 3.3 Model calibration and validation 4 3.5 Results and discussions 9 3.1 Surface elevation sỉ 3.2 Current s CONCLUSIONS AND RECOMMI DATIONS. os CONCLUSIONS a RECOMMENDATIONS “ REFERENCES.
66 APPENDICES 68 LIST OF FIGURES Figure 1-1. Vung Tau- Go Cong Sea dike project (Souree: Google Earth 2010). Sai Gon- Dong Nai river basin 12 Figure 1-3, Map showing the Vung Tau Go Cong sea dike project (Source: Son (2012). Overview of the station net realized during the cruise in April 2007.
Study area and bathymetry of computational domain. _ Figure 3-3, Locations of river boundaries and sea boundaries 39 Figure 3-4, Hydrographs at river boundaries. Model calibration: Comparison between simulated and measured water level at Vung Tau gauge station (ME mÙ3, 17/10/2000 01:00-20/10/2000 01:00) .43 Figure 3-6, Surface elevation in model calibration, 17/10/2000 01:00-20/10/2000 01:00 (let hand-flood tide; right hand-ebb tide) 4s Figure 3-7, Current speed in model calibration, 17/10/2000 01:00-20/10/2000 01:00 (left hand-flood tides right hand-ebb tide), 44 Figure 3-8, Model validation: Comparison between simulated and measured water level at Vung Tau gauge station ( 21/10/2000 01:00-24/10/2000 01:00), 46 Figure 3-9, Surface elevation in model validation (left hand-flood tide; right hand- ebb tide. so sow AT Figure 3-10.
Current speed in model validation (lft hand-lood tide; right hand-ebb tide) a Figure 3-11. Computational domain in the second scenario, with sea dike 48 Figure 3-12 Locations of exported results s0 Figure 3-13 Surface elevation at ebb tide, 10/20/2000 04:00, first scenario SI Figure 3-14 Surface elevation at ebb tide, 10/20/2000 04:00, second scenario sl Figure 3-15 Surface elevation at flood tide, 10/21/2000 17:00, first scenario Figure 3-16 ‘Surface elevation at flood tide, 10/21/2000 17:00, second scenario. Figure 3-17 Comparison water level elevation between two scenarios at PI-P4. Figure 3-18 Comparison water level elevation between two scenarios at P5-P8.
54 Figure 3-19 Comparison water elevation between inside and outside reservoir , 35 Figure 3-20 Comparison water elevation between inside and outside reservoir, 35 Figure 3.21 Current speed at ebb tide, 10/24/2000 02:00, first scenario, 5g Figure 3-22 Current speed at ebb tide, 10/24/2000 02:00, second scenario Figure 3.23, Current speed at flood tide, 10/21/2000 17:00, first scenario. Figure 3-24, Current speed at flood tide, 10/21/2000 17:00, second scenario so Figure 3-25 ‘Comparison current between two scenarios at PI-P4. 60 Figure 3-26, ‘Comparison current between two scenarios at PS -P8 61 LIST OF TABLES Table 1-1 Distribution of annual monsoon Table 3-1 Locations ofriver boundaries and Vung Tau gauge station. Results in Nash- Suteliffe coefficient.
43 Table 3-3 Parameters after model calibration. Design parameters of sea dike and sluice in the second scenario 49 Table 3-5 Locations of points to export results. Table 3-6, Comparsion estreme watel level between two scenarios at P1-PS. ‘Comparison extreme current speed between two scenarios at PI-P§ “ : INTRODUCTION 1.1 Background ‘The downstream of the Dong Nai river and the Vam Co river covering, 10000 km” plays an important role in the society and the economy of Viet Nam (Figure 1-1).
This area includes Ho Chỉ Minh City, Dong Thap Muoi (belonging to Mekong Delta River), Vung Tau - Go Cong area and Tien Giang, Long An province with dense populations and concentration of business as well as intensely agricultural productions Figure I-1. Vung Tau- Go Cong Sea dike project (Sour + Google Earth 2010) The relative low elevation of this area in combination with the increasing, extraction of drinking water and the flooding problem from the effect of sea level rise as well as salt intrusion are now of the primary concern of these areas. The low-lying land area is located near the mouth of the large branches of the Dong Nai and Vam Co River system (Figure 1-2) and therefore it is strongly affected by the variation of the flow in the river and, an even more dominant factor, the tidal current, Large reservoirs have been built upstream retaining the flood flow, leading to a decrease in the amount of average flood flow. Conversely the effect of the tidal current is increasingly higher, resulting in salt intrusion and a lack of fresh water.
Human intervention in this area also diverts the direction of the flow and tidal current into the river, increasing water level at high tide and reducing water level at low tide causing an increase in the tidal range in the river mouths. The higher the tidal ranges, the more tidal energy, the less time tides need to transport from the sea to the river basin, The overall impact is that more areas are suffering from tidal flooding, Moreover, the effect of the sea level rise will add to these impacts and make it more severe. In short, in the present situation, the study area is located in a complicated system of many estuaries which consist of intensive rivers and channel networks therefore it is strongly affected by tide from the sea. Moreover this isa low land area therefore it is difficult for draining, Human intervention including groundwater withdrawal and channel accretion have also contributed to land subsidence and, even lowers the elevation of the area In other words, tidal influences and salt intrusion problems due to sea water penetrates are two main concems of this area.
12 Natural conditions Wind regi The study area is affected by two main direction of wind: Southwest ‘monsoon and Northeast monsoon (Table 1-1) Table 1-1. Distribution of annual monsoon Dry season | ‘Transition ‘Wet season Dry season 1| H |H| IV (V|VI VH|VH|IX|X XI XI NE monsoon | Transition ‘SW monsoon NE monsoon The southwest monsoon often starts in May and lasts to the end of September. At offshore region, the main direction of wind is west with the maximum velocity of 10-12m/s. In coastal area, due to continent the main direction of wind is Southwest and the average wind velocity and maximum wind velocity are 4-6 m/s and 8-10 n/s respectively.
The northeast monsoon often starts in September and lasts to the end of March. At offshore region, the main wind direction is Northeast and average wind velocity is 9-11 m/s, the maximum wind velocity is above 20 m/s. In the coastal area, the main direction is Northeast and East, the average velocity and maximum velocity are 8-10 m/s and 12-14 mís respectively. Oceanic regime and sedimentation.
The study area is strongly affected by tide from the East sea, the monsoon as well as flow regime in the Mekong and Sai Gon ~ Dong Nai rivers. The total flow includes tidal flow, ocean current, river flow and coastal drift The tidal regime is semi-diumal tidal, tidal range is 3.6m, The velocity of flood tide is 0.9 mls, up to 1.2 m’s and velocity of ebb tide is 15-18 mis, Respective to inconstant distribution of annual volume water, flow regime in Mekong and Sai Gon - Dong Nai rivers fluctuates following seasons. For example, at Tan Chau station the discharge is up to 20.000 m‘/s in wet season, meanwhile the discharge is 3.000 m’/s in dry season, In wet season, the sediment content is higher than that in dry season.