Design of a flood-retaining hydraulic structure at Phú Dinh

Abstract

Ho Chi Minh City is flooded on a regular basis due to the lack of flood protection. Plans have been made to protect the city from flooding in the future and therefore a barrier is built at Phu Dinh. This barrier needs to fulfil three requirements. Firstly it should protect HCMC against a flood, as well resulting from tidal waves as from peak rains. Secondly during the dry season it should keep the water level above a minimum. Thirdly, while performing the first two requirements, navigation should be hindered barely. In order to find the ideal design first 3 variants were selected from 17 options with a MCA. Two of these variants were merged because of additional research. Variant A, two locks and a culvert dam, and variant B, a lock with a tidal barrier, were made into a preliminary design. These designs were compared with a new MCA and variant A was chosen as the best design. Variant A consists of a big and a small lock in order to keep the navigation possible during flood protection. When possible the big lock can be opened for free navigation due to its lift gates. The small lock will be built with double mitre gates. Between the locks a dam with culverts is built to close of the river and provide the needed conveyance area for the outflow of rain water. This design meets the requirements stated about flood protection, outflow regulation and navigation. The risks during operation are low because of the double set of doors in both locks. Because there are two locks the chances are low that the navigation will ever be totally obstructed. The estimated costs of this variant are VND 1150 billion (€ 46 million). It is recommended to look at improving the barrier by building a bridge over it. Surrounding the barrier there are no embankments present, therefore in order for the barrier to function these have to be built. Further the application of pumps in the culvert can lower the risks of a flooding due to rain, when investigating this it is important to do research on the catchment and conveyance area in the city the barrier has to deal with. During the investigation it was hard to make a good estimation about the importance of stakeholders and MCA criteria. Therefore more experience with the local environment could improve the design.