ABSTRACT OF DOCTOR OF PHILOSOPHY THESIS

Name of author:        Pham The Vinh

Supervisors:              Prof., Dr. Nguyen An Nien; Prof., Dr. Tang Duc Thang

Name of thesis:         Research on the role of tidal flats to the water level and discharge of Saigon - Dongnai river

Specialization:         Water Resources Engineering               

Code:                       9-58-02-12

Postgraduate organization: Vietnam Academy for Water Resources

CONTENT OF THE ABSTRACT

1. Object and purpose of the thesis

1.1. Research purposes

- The analysis is based on a scientific basis showing the effects of tidal changes on water level and discharge in the river.

- Based on the hydraulic model established for the study area, simulating and assessing the impact of tidal flats on water levels and discharge in the downstream of Sai Gon Dong Nai river basin

1.2. Research object

Research object on the tidal flats: are limited to tidal flats in the downstream of Sai Gon - Dong Nai river basin.

2. Research methodologies

- Inheritance method.

- Synthesis and collection method.

- Analytical method.

- Mathematical model method.

- Practical contact comparison method.

3. The main results

3.1. Scientific contribution

- Based on scientific basis analysis, hydraulic simulation, clarifying the impact of tidal flats on water level and discharge in the downstream of Sai Gon - Dong Nai river basin.

- Providing arguments to confirm the impact of tidal flats on the water level, the discharge on the downstream is very large and cannot be ignored.

3.2. Practical contribution

- The results of the thesis are published to provide information to support researchers, consultants, planners and managers to identify changes in tidal flats that greatly affect on the water levels. and river flow. This impact in recent years is much greater than that of climate change.

- The results of the thesis are applicable to the research, design, construction, exploitation and operation of works in the downstream of Sai Gon Dong Nai river basin in particular and for low-lying areas, impact of tides.

3.3. New findings of the research

- Establishing the relationship between tidal flats with the water level and discharge in the river.

- Calculating the impact of tidal flats on water levels and discharge in the downstream of Sai Gon - Dong Nai river basin.

4. Conclusions and further researches

4.1. Conclusions

- The terrain of river bed and flats along the river always change under the influence of natural factors and human, these changes affect the water level and flow rate in the river. Forms of terrain can be mentioned as: (i) River cross-section terrain including river bed cross section and side flats; (ii) Low-hollow areas at the upstream are flood retention  areas; (iii) Downstream of areas affected by tide are tidal flats. The thesis focuses on the change of water level and flow rate in the river when tidal flats are narrowed.

- The thesis has used theoretical analysis to determine the relationship between the width of tidal flats and water level and flow rate in the river. The thesis also uses land use documents through local data collection and satellite image analysis to identify tidal flats. To clarify the impact of tidal flats on the water level and flow rate in the river, the thesis has built test model to simulate tidal flats in many cases. For applying practical calculation for the downstream of SG-DN River, the thesis uses hydraulic model (1-D, 2-D) to describe the impact of tidal flats on the water level and flow rate in the main river at the downstream ofSG-DN River. The thesis also simulates the calculation of the largest water level in the future when tidal flats disappear and proposes solutions to reduce the water level in the river based on the viewpoint of restoring flood plains.

- Thus, it can be seen that tidal flats in the study area are a very important factor affecting the tidal regime. According to analysis results, the human impact in narrowing tidal flats causing the largest water level is larger than the impact on rising of sea level. Therefore, human need to have more appropriate concepts and behavior in the exploitation and protection of tidal flats in the area. This study is applied to the downstream of SG-SE river, but in principle and general rule, it can be applied to other river basins with tidal influence.

4.2. Further researches

Factors of land subsidence, deformation of the river bed, wind impact, salinity composition, shape of tidal flats and structures affecting the propagation of tidal wave into estuaries have not been mentioned in this study. In next studies, more studies on these factors should be taken to give complete results.

See detail: SUMMARY OF TECHNICAL DOCTOR THESIS - PHAM THE VINH