ĐÁNH GIÁ SỰ TƯƠNG TÁC GIỮA KHỐI NƯỚC VÙNG CỬA SÔNG MÊ KÔNG VÀ VÙNG NƯỚC TRỒI NAM TRUNG BỘ

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1 ĐÁNH GIÁ SỰ TƯƠNG TÁC GIỮA KHỐI NƯỚC VÙNG CỬA SÔNG MÊ KÔNG VÀ VÙNG NƯỚC TRỒI NAM TRUNG BỘ Lê Đình Mầu 1, Bùi Hồng Long 1, Thomas Pohlmann 2, Bùi Xuân Thông 3, Hartmut Hein 5, Đoàn Văn Bộ 4, Nguyễn Kim Vinh 1, Birte Hein 2,5, Nguyễn Văn Tuân 1, Phạm Sỹ Hoàn 1 và Nguyễn Chí Công 1 (1): Viện Hải dương học, 1 Cầu Đá, Nha Trang; (2): Trường Đại học Tổng hợp Hăm Buốc, 53, D-2146 Hăm Buốc, CHLB Đức; (3): Trung tâm KTTV biển, 62 Nguyễn Chí Thanh, Đống Đa, Hà Nội; (4): Trường Đại học KHTN, 334 Nguyễn Trãi, Hà Nội; (5) Viện Thuỷ văn Liên Bang, Am Mainzer Tor 1, D-5668 Koblenz, CHLB Đức ledinhmau.vnio@gmail.com Tóm tắt: Báo cáo trình bày một trong những kết quả nghiên cứu chính của Nhiệm vụ hợp tác quốc tế theo Nghị định thư Việt Nam-CHLB Đức do Viện Hải dương học chủ trì. Giai đoạn (Phase-I): nghiên cứu cấu trúc, biến động và những hiệu ứng sinh thái của vùng nước trồi mạnh Nam Trung Bộ (NTB). Giai đoạn (Phase-II): nghiên cứu vùng cửa sông Mê Kông và các quá trình tương tác giữa chúng và vùng nước trồi NTB. Bằng phương pháp phân tích đặc trưng các khối nước, phân tích ảnh viễn thám và mô hình hoá cho thấy địa hình ven bờ, thuỷ triều, lưu lượng nước sông, hoàn lưu theo mùa ven bờ Tây Biển Đông là những tác nhân chính trong sự tương tác giữa khối nước vùng cửa sông Mê Kông và vùng nước trồi NTB. Nhận định bước đầu cho thấy phạm vi tương tác của hai khối nước trải dài từ Bình Thuận đến Cà Mau và ra đến đảo Phú Quý và Côn Đảo. Abstract: ASSESSMENT OF THE INTERACTIVE PROCESSES BETWEEN MEKONG RIVER MOUTH AND UPWELLING WATER MASSES This paper presents one of the main study results of the co-operative project between Vietnam and Germany on oceanography which was carried out by Institute of Oceanography, Nhatrang, Vietnam. Phase I (23-26): study on the structure, variation and ecology-environmental effects of Vietnamese upwelling area. Phase-II (27-21): study on the hydro-litho-dynamic, and ecology-environmental features in the Mekong River mouth area and the interactive processes between Mekong River mouth and upwelling water masses. Using water mass analysis, remote-sensing technique and modeling methods, study results show that the features of nearshore bathymetry, tide, river discharge and monsoonal circulation along the west coast of the South China Sea are the main causes of the interactive processes between Mekong River mouth and upwelling water masses. Preliminary studies show that the interactive processes extend to the area between Binhthuan and Camau and from the coast to Phyquy and Condao Islands. I. INTRODUCTION Mekong River mouth and upwelling areas are the most important regions for economical development and environmental protection of Vietnam. The governing processes, structure and variation of the upwelling area, the hydro-litho-dynamical processes in the Mekong River mouth area, the interactive processes between Mekong River mouth water and upwelling 115

2 water masses and their ecology-environmental effects are of most concern for oceanographers in Vietnam and internationally. To solve these scientific questions the co-operation project between Vietnam and Germany on oceanography was established. Phase I (23-26): study on the forming processes, structure, variation and ecology-environmental effects of upwelling area. Phase-II (27-21): study on the hydro-litho-dynamic processes, ecologyenvironmental features in the Mekong River mouth area and the interactive processes between Mekong River mouth and upwelling water masses. The co-operative project was carried out based on most advanced measuring instruments, data analysis and modeling techniques. The co-operative project results form an important scientific base for marine economical development and environmental protection of Vietnam. The content of this paper is as follows. 1. General scientific results of the co-operative project. 2. Assessment of the interactive processes between Mekong River mouth and upwelling water masses. II. DATA AND METHODS + The main study results of Phase-I (23-26) were taken from the final scientific report of the project [1]. + The main study results of Phase-II (27-21) were taken from the final scientific report of the project [6]. Table 1: Data analysis and modeling methods S.No. Problems Methods 1 - Statistic of longtime measured meteo-hydrologic data. - Water masse feature - Gamble Distribution Function [2]. - Curved line T-S method [3], [7] 2 Circulation with large scale for the South China Sea Model circulation-3d (developed) 3 Circulation with meso scale for Models: HAMSOM (Hamburg University, study area Germany) and DELFT-3D (Holland) 4 Transport of suspended Models: ECOMSED (HydroQual, Holland) and particulated matters HAMSOM (Module: SPM) 5 Hydro-ecology-environmental Model: ROMS (USA) processes 6 Water exchange rate at a section Ekman formula [3], [7] 7 Stability of water column Model of Potential Energy Anomaly (Hamburg University, Germany) In there, to solve the problem: Assessment of the interactive processes between Mekong River mouth and upwelling water masses the following data and methods were used: Wind data were collected from Condao station ( ) and Phuquy Island ( ). Mekong River discharge data were collected from Cantho and Mythuan stations ( ). Hourly water level data were collected from Vungtau station ( ). Bottom topography in the study area was taken from hydrographic map with scale of 1/5. (Published in 24). Sediment characteristics were taken from the cruise (9/29) which was carried out by the Institute of Oceanography. Also, the other related data have been collected from different projects. Criteria to classify the brackish and sea water masses was 32 psu [8]. The method of data analysis and modeling were used are as follows (table 1). 116

3 III. STUDY RESULTS 1. Main study results of Phase-I (23-26) and Phase-II (27-21) a. Origin of the project: In the year of 23 the Ministry of Science and Technology (Vietnam) and Development Fund DFG (Germany) have been signed a co-operative program on marine research with the main contents as follows: - Impact assessment of the short-time and long-time variations of the atmosphere-oceancontinent system to hydrodynamic processes and primary productivity in the upwelling area. Developing the suitable models. - Clearing the upwelling related phenomena and their interaction with adjacent regions. - Enhancement of bilateral co-operation between Vietnam and Germany on marine research to upgrade marine research potential of Vietnam. b. Main study results of Phase-I (23-26): To enforce the co-operation program, from 23 to 26 Vietnam and Germany have been carried out the project with title: Study on the upwelling phenomenon and related processes on the South Vietnam shelf. Field expedition were carried in a large area extending from Phuyen to Vungtau and from the coast to about 1 miles offshore, up to a water depth of 1m (especially sediment trap was deployed at water depth of 3m) for 4 seasons with 9 cruises. Meteo-hydrodynamical, biology, ecology-environment, geology, etc. parameters have been collected. Oceanographical parameters were collected by modern instruments such as: + Ship: Sonne (26), Nghien cuu bien (23, 24, 25), NCB-95 (26, 27), HQ683 (27) (Fig.1). + Measuring Instruments: CTD + Fluoro-meter + Backscatter, Current meter profiler (ADCP). Whereby, T, S, v represent physical parameters, fluorescence biological and Turbidity, SPM geological ones (Fig.2). + Physical Oceanography: - It was the first time the two layers structure of seasonal varying current system along Southern Central Vietnamese coast has been studied so intensively (offshore boundary is located about 8km offshore, the depth of surface layer is about of 5 to 6 m). - Circulation model a 3D baroclinic model using the nonlinear method was applied to investigate the upwelling phenomenon. Modeled results show that under the influence of SW monsoon along the southern Central Vietnamese Coast the upwelling phenomenon occurred especially from June to August (with an offshore directed velocity V 6cm/s in the surface layer). a. Nghien Cuu Bien b. NCB-95 c. HQ638 d. Sonne Figure 1: Vessels participating in project Phase-I (23-26) 117

4 Figure 2: Some of the instruments which were deployed + Measured stations are shown in Fig.3 a. Location of measured stations b. Location of Biogeochemical flux traps Figure 3: System of measuring stations during Phase-I (23-26) - Method of empirical orthogonal function (EOF) was used to indicate the main structure of SST in the South China Sea under the influence of monsoonal winds and the effects of global climate change. - The region of strongest upwelling along southern Central Vietnamese coast was identified by using the wind stress data from Pacific Center for Fishery. - Variation of SST, Chlorophyll-a, Primary Production in the surface layer of the southern Central Vietnamese coast were studied by using the data extracted from MODIS and SeaWiFS. - Seasonal circulation patterns in the southern Central Vietnamese water were clarified by using MCC method to extract the data from AVHRR. Study results show that there exists a permanent large scale anticyclonic current in the study area throughout all seasons. 118

5 + Ecology-Environment: - During July a strong intrusion phenomenon of nutrients from deep layers to surface layer exists in the upwelling area. This phenomenon affected the phosphate content; nutrients will settle at the bottom and seriously affect the ecological-environmental condition especially during summer while the oxygen content is low. - Distribution of nutrients reflects the intrusion mechanic from deep water layers to the photosynthetic layer. - Primary production in the coastal water of Khanhhoa-Ninhthuan is dependent on the intensity of upwelling. - During strong upwelling events, two centers of highest primary production are formed in Khanhhoa-Ninhthuan waters, chl-a content is highest in the upwelling season. + Marine planktons and particulated flux: - Many species of planktons and small fishes have been detected. - Highest density of cells occurred in the nearshore zone and at the layer between 2 and 4 m during the upwelling period. - Highest biomass of plankton occurred in the nearshore zone from Tuyphong to Khanhhoa and the offshore region of Phuyen waters during upwelling period. - Highest quantity and density of spawning occurred in the nearshore zone from Camranh to Vungtau and at surface layer during the upwelling period. - Highest density of marine algae (spherical lime and silic) occurred during upwelling period along southern Central Vietnamese Coast. - Publication of a monography about the upwelling area and its related processes. Project results obtained in Phase-I play an important role as they are of high scientific and practical values, because they contribute to the understanding of the upwelling phenomenon off southern Vietnam. However, the remaining problems which have to be tackled in further studies are: - Seasonal variations of the interactive processes between the circulation at the west coast of the South China Sea with Mekong River water and upwelling water masses. - The processes forming the hydrological fronts and their interaction with involved water masses. - The question whether the upwelling area has received the material from Mekong River system. - Enlargement of the data base for the upwelling region including interactive processes between upwelling and Mekong River mouth water masses. c. Main study results of Phase-II (27-21) The joint project in Phase-II (27-21) continued with the study of the remained problems of Phase-I (23-26) with the title: Study on the coastal processes in the Mekong River mouth area and the interactive processes between Mekong River and the upwelling water masses. The main objectives of joint project are as follows. 1. To assess the interactive processes between Mekong River and upwelling water masses; 2. To assess the frontal features: structures and variations; 3. To construct a scientific base for the assessment and prediction of the marine resources for sustainable development of coastal economic; 4. To improve the potential of Vietnamese Oceanographers to perform studies, applications and international cooperations. 119

6 The main organizations that participated in the joint project are shown in Table 2. Table 2: The main organizations participated in the joint project Serial No. Name of Organizations Responsibilities A. Vietnamese side 1 Institute of Oceanography Responsibility of all joint project activities 2 Center for Marine dynamic and Water masses and hydrological fronts environment, College of Science, Vietnam National University, Hanoi. 3 Institute of Marine Resources and Construction of the data base Environment 4 Center for Meteo-hydrological data Supply and analysis of long term (National Center for Meteo-hydrology) meteo-hydrological data 5 College of Science, Vietnam National University, Hochiminh City Survey and computation of wave characteristics B. German side 1 Institute of Oceanography, Hamburg Survey and modeling of meteo-hydrodynamical University, Germany processes 2 Institute of Bio-geo-chemical, Hamburg University, Germany Survey and study on sedimentation processes 3 Institute of Marine Science Baltic Survey and study on nutrients, primary Warnemünde, University of Rostock, production, biology, and hydrochemical Germany features - Field investigation: 4 cruises were carried out during low (4/27, 4/21) and high (9/28, 9/29) river discharge periods, sampling the following parameters: 1. Meteo-hydro-dynamical: Wind, wave, current, water temperature-salinity, water transparency, etc.); 2. Nutrients: Total P (mg/l), Nitrate (NO 3 -N mg/l), Nitrite (N-NH 4, N-NO 2 ), Total N (inorganic, organic- mg/l). 3. Ecology: Chlorophyll a (mg/l), SPM (C g/m 3 ), Primary production (C g/m 3 /day. raw), Dissolve Oxygen, Silic; 4. Plankton (quantity and quality); 5. Geo-morphological condition (bottom sediment) Field investigation stations are shown in Fig.4a,b,c. The main study results of Phase-II are as follows. - The long-term data of wind, typhoon strength, wave, sea water level (SWL), Mekong River discharge, rain fall, etc. have been collected and analysis to estimate the features of meteohydrodynamical processes in the study area. Statistical results show that the study area is strongly affected by monsoonal winds (NE monsoon from October to April, SW monsoon from June to August, May and September are transitional periods). Typhoons occur from October to December, especially in November (55%). In general, this area is less affected by typhoon (.57 typhoons/year) than the northern parts of Vietnam. High Mekong River discharge occurred from June to November, especially in September with Q max 15,8 m 3 /s at Mythuan Station (9/21) and 15, m 3 /s at Cantho Station (9/21). Low river discharge occurred from December to May, especially in March and April with Q min 8 m 3 /s at Mythuan Station (3/25) and 76 m 3 /s at Cantho Station (4/24). The tidal regime is irregular semidiurnal with a maximum value of the SWL of 49 cm occurring in November. 12

7 11 Phanthiet Tp.HCM Tiengiang Vungtau Phuquy Island 1 Soctrang Baclieu Bentre Travinh Condao Island : depth contours (m) : measured stations : continuous stations Figure 4a: System of measured stations during Phase-II: (4/27) Phanthiet 1.5 Tp.HCM Vungtau Soctrang Travinh AS Bentre b 16 17b : depth contours (m) : measured stations (floating) : measured stations (anchorage) : continuous stations Figure 4b: System of measured stations during Phase-II: (9/28)

8 Phuquy Island : depth contour (m) : measured stations : continuous measured stations 5 Km Scale: 1/2 Baclieu Tien River Hau River Soctrang Tp. HCM Vungtau Tiengiang 1 2 Dai Mouth (I) 3 Bentre 4 Hamluong Mouth Cunghau Mouth Travinh 7 (II) 8 Dinhan Mouth Soaøirap Mouth Phanthiet Camau Condao Island Figure 4c: System of measured stations during Phase-II: (9/29 and 4/21) - Hydro-litho-dynamical processes in the study area were affected by monsoonal wind, river discharge, tides and bottom topography. During the SW monsoonal wind period and high river discharge, Mekong River water spreads up to about 8 to 1 km offshore inclining in the northern part of study area towards the transect between Kega Headland and Phuquy Island. During the NE monsoonal wind period under the effect of the cold boundary current flowing parallel to the southern Vietnamese Coast from north to south, the Mekong River water is constrained to the coast and directed to Camau Headland. - In general, nutrients were mainly discharged from Mekong River. The content of Suspended Particulate Matter (SPM) in the study area is approximately between.7 and mg/l, with an average value of 6.92 ± 5.6 mg/l. This SPM concentration is less than 5 mg/l (permission threshold for critical nearshore water quality). During high river discharge period, the concentration of chlorophyll-a and primary production rates are increasing from south to north in the study area. During low river discharge period, the study area is a poor-nutrients region. Concentration of plankton is 1 times higher during high river discharge periods compared to low river discharge periods. Plankton is distributed mostly in the northern part during SW monsoon and high river discharge, whereas, during low river discharge periods it is distributed only around the river mouths. - Mekong River mouth area is a region where water masses of the northern and southern South China Sea interact with upwelling water, fresh water from river run-off. The interaction of the above mentioned water masses induced the formation and distribution of seasonal hydrological fronts. The density of total phytoplankton was mainly determined by silic algae, whereas the density of toxic algae was low. - Mekong River mouth area can be divided in to 3 regions depending on the affect of river water. They are river water, intermediate and sea water dominated regions. Each region has its specific ecology-environmental feature and bio-resources. - The features of upwelling and Mekong River mouth water masses and their interaction are depended on the western boundary current regime of the South China Sea and Mekong River discharge. 122

9 - During NE monsoonal period (low river discharge), the water mass from the northern part of the South China Sea with its characteristics of low temperature and high salinity follows the western boundary current to the Mekong River estuary with characteristics of low salinity and high temperature. Due to the interaction processes, it formed a water mass with characteristics of T 25 C, S 34 psu. This water mass covered the area from Phanthiet to Camau, and extends as far as about 2 to 25 km offshore, except in the Mekong River mouth areas. Mekong River water discharge is constrained to the nearshore and flows to Camau Headland. - During SW monsoonal period (high river discharge) the characteristics of governing processes are the dispersion of Mekong River mouth water to the upwelling region under the affected of the western boundary circulation of the South China Sea from south to north. Study results show that the extent of Mekong River mouth water mass with characteristics of T 29 C and S 32 in case of high river discharge and prevailing SW monsoonal wind can reach to Phanthiet and enter the Condao and Phuquy Island region. The transect Phanthiet-Phuquy marks the front of two water masses. In case of highest Mekong River discharge (1/25) the extent can be as far as 2 km off the coast. The thickness of Mekong River water plume with a characteristic of S 32 psu [8] at the transect Longhai (off Vungtau) was about 1 m. During the SW monsoonal period, the water mass along the southern Central Vietnamese Coast has a T-S characteristic of C and 31-34,8 psu from surface to 2 m depth. These T-S values are similar to the T-S values in the deep layer of the Mekong River mouth shelf region. This is a proof of the dispersion of Mekong River mouth water to the upwelling region. Preliminary calculations show that during the high Mekong River discharge period and prevailing SW monsoonal winds (V = 6.8 m/s) the mass transport through the transect Longhai (off Vungtau) was Q m 3 /s (1.2 Sv). - The Mekong River mouth is a region of high primary production and biodiversity. However, the exploitation level of bio-resources was critical. The impacts of global climate change especially the SWL increase and lack of scientific base for the construction of hydroelectric power dams in the upstream reaches of the Mekong River induce a significant sea water intrusion as well as coastal erosion. These problems will form the main challenge for a future sustainable development in the Mekong River delta. d. Some comments for the joint project: - The joint project carried out was necessary to obtain the concerned objectives from both parties. In general, the main objectives of the joint project have been achieved as they are: a) Preliminary the understanding of the features related to the upwelling phenomenon and its interaction with adjacent regions, b) Estimation of the main hydro-litho-dynamical processes and features of ecology-environment in the Mekong River mouth area, and c) qualitative assessment of the interactive processes between Mekong River mouth and upwelling water masses. - The joint project carried out was an enhancement for the bilateral co-operation between Vietnam and Germany on marine research and upgraded the marine research potential of Vietnam, especially the application of modern equipment and study methods, like numerical models [4]. However, some shortcomings have occurred during the execution of the joint project, namely: + Since the joint project proposal was approved from each country separately, unfortunately the financial support was not available for the same time. As an example, the joint project Phase-II was approved in Germany starting from 27, but for Vietnamese side it took until 29 before Phase II was approved. One more example: during 2-23 the joint project between Vietnam and India was also approved at different times (in the year of 2 the Vietnamese side was approved, but the Indian side was approved in 21). These problems 123

10 Kiªn Giang seriously affected the bilateral co-operation works. In fact, this situation led to independent works of each side, consequently the effectiveness of the joint project with regard to scientific and financial aspects was not optimal. + In general, the collaboration had worked nicely during field surveys, whereas, the Vietnamese role in data analysis, professional works and publications was rather limited and was mainly conducted by the foreign partner. 2. Interaction processes between Mekong River Mouth and upwelling water masses This section illustrates some study results of the interaction processes between Mekong River Mouth and upwelling water masses During NE monsoonal period The study results are shown in Fig. 5a,b,c Km Tp. HCM Baø Ròa-Vuõng Taàu Vòng Tµu 1 Soâng Tieàn Soâng Haäu Tieàn Giang Beán Tre 9.5 Soùc Traêng Traø Vinh Baïc Lieâu 9 Cµ Mau Coân Ñaûo Figure 5a: Distribution of the thickness (m) of Mekong River mouth water in April 21 (S 32 psu) C Figure 5b: Distribution of surface temperature ( o C) during January Figure 5c: SPM concentration in January (Model: HAMSOM [5]) 124

11 Kiªn Giang The main findings are that during the NE monsoonal period the water mass from upwelling area spreads into the Mekong River mouth region and the Mekong River water is constrained to the coast and flows in southward direction up to Camau Headland (Fig. 5b,c). During the transition period in April 21 the Mekong River water occurred only around the river mouth area (Fig. 5a) During SW monsoonal period The study results are shown in Fig. 6a,b,c,d,e Km Tp. HCM Baø Ròa-Vuõng Taàu Vòng Tµu 1 Soâng Tieàn Soâng Haäu Tieàn Giang Beán Tre 9.5 Soùc Traêng Traø Vinh Baïc Lieâu 9 Cµ Mau Coân Ñaûo Figure 6a: Distribution of the thickness (m) of Mekong River mouth water in September 29 (S 32 psu) Figure 6b: Distribution of salinity (S psu) at continuous station LT-I during 14h/19/8 12h/2/8/29 (Vungtau transect) 125

12 W E -1 Tr.1 Tr m Tr.3 Tr.4 Tr.5 Tr.6 Tr.7 Tr.8 Tr.9 o N Figure 6c: Distribution of salinity (S psu) in the transect Dai Mouth Lagi (8/29) Tr.1 Figure 6d: SPM concentration on 24/9/29 (MODIS Image) Figure 6e: SPM concentration in August (Model: HAMSOM) During SW monsoonal period and high river discharge, the main study results are that the water mass from Mekong River mouth region spreads into the upwelling region. In September 29, the Mekong River mouth water (S 32 psu) extended as far as 1 km off the coast with the thickness of about 15 m (Fig. 6a), and spreads to the north up to Lagi water (Fig. 6c) with the thickness of about 1 m. During August 29 an intrusion of Mekong River water was observed on the Vungtau transect with a thickness from surface to the bottom (Fig. 6b). However, this study was still not sufficient to quantify the total volume of Mekong River water spreading into the upwelling region. IV. CONCLUSIONS - The joint project carried out was necessary to obtain the concerned objectives from both parties. In general, the main objectives of the joint project have been achieved as they are: a) Preliminary the understanding of the features related to the upwelling phenomenon and its interaction with adjacent regions, b) Estimation of the main hydro-litho-dynamical processes and features of ecology-environment in the Mekong River mouth area, and c) qualitative assessment of the interactive processes between Mekong River mouth and upwelling water masses. The joint project carried out was an enhancement for the bilateral co-operation between Vietnam and Germany on marine research and upgraded the marine research potential of Vietnam, especially the application of modern equipment and study methods, like 126

13 numerical models. However, some shortcomings have occurred during the execution of the joint project, these problems have to be solved in the future. - During the NE monsoonal period the water mass from upwelling area spreads into the Mekong River mouth region and the Mekong River water is constrained to the coast and flows in southward direction up to Camau Headland. In contrast during the SW monsoonal period and high river discharge, the main study results are that the water mass from Mekong River mouth region spreads into the upwelling region. However, our study was still not sufficient to quantify the total volume of Mekong River water dispersion into the upwelling region. ACKNOWLEDGEMENTS The authors gratefully acknowledge all colleagues for their kind help and encouragement throughout the preparation of this paper. REFERENCES 1. Bui Hong Long, Study on the structure, variation and ecology-environmental effects of Vietnamese upwelling area. Final report of the joint project between Vietnam-Germany, Phase-I: Nhatrang, 26, 223 ps. 2. CEM, Coastal Engineering Manual, 26 (replacement to Shore Protection Manual 1984). Publication Number: EM U.S. Army Corps of Engineers (USACE). 3. Egorop, N.I, Physical Oceanography. (In Vietnamese), Volume I and II, 1981, University and Training School Publisher, Hanoi. 4. Hein, H., T. Pohlmann; B.H. Long, N.K. Vinh, Inter-annual variability in the South China Sea and its consequences on the Vietnamese upwelling area, 211. Submitted to: Global and Planetary Change. 5. Hein, H., B. Hein, T. Pohlmann, Recent sediment dynamics in the Mekong ROFI, 211. Submitted to: Global and Planetary Change. 6. Le Dinh Mau, Study on the hydro-litho-dynamic, and ecology-environmental features in the Mekong River mouth area and the interactive processes between Mekong River mouth and upwelling water masses. Final report of the joint project between Vietnam- Germany, 211, Phase-II: Nhatrang, 18 ps. 7. Pickard, G. L. and W. J. Emery, Descriptive Physical Oceanography. An Introduction, Fifth enlarged Edition (in SI units), Pergamon Press, 32ps. 8. Robinson, M. K, The physical oceanography of the Gulf of Thailand, NAGA Expedition. La Jolla, California: NAGA Report, 1974, v. 3, P. 1, p