Project Hue

Report and field study on the water related problems and solutions in and around the Cau Hai lagoon and the Tu Hien inlet, Vietnam

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The Tam Giang-Cau Hai lagoon system, lying in the Thua Thien-Hue province in central Vietnam, is affected by a tropical monsoon climate. This among others is the reason the Cau Hai Lagoon area has a long history of floods and other water related problems. Inhabitants are very dependent on the lagoon, as the main sources of income of people living in the region are fishing, agri- and aquaculture. The project goal has been formulated as follows: Finding an economic as well as technical feasible solution to reduce the water related problems, specifically navigability, salt intrusion and floods, in and around the Cau Hai Lagoon and the Tu Hien inlet and thereby improving the economic development of the region. Concerning flood risk, navigability and salt intrusion the inlet stability and size are important aspects. Using an echo sounder the bathymetry of the inlet has been measured. The measured size of the inlet was one of the input parameters for the hydraulic model that has been set up. This basic model of the Cau Hai basin system was made to test some alternative solutions for the Tu Hien inlet. The different solutions were simulated for five different scenarios. These scenarios include average dry season conditions, average wet season conditions and multiple extreme events. The output of the model for the different alternatives was used to rate the alternatives for a couple of criteria in a Multi Criteria Analysis. Other criteria of the MCA are qualitatively rated. The most promising alternative proved to be the one including a jetty at the northern side of the Tu Hien inlet in combination with a bank protection at the other side. In this way a large part of the littoral drift is blocked, enlarging the equilibrium cross-section of the inlet. This in turn results in a better flood evacuation capacity, navigability and water quality in the lagoon. For both mentioned elements a preliminary technical design is made, resulting in the stone class needed for the armour layers, dimensions of the toe and characteristics of the filter.