Development west coast Taiwan: Redesign coastal area between Da’an River and Dajia River

Development west coast Taiwan: Redesign coastal area between Da’an River and Dajia River

Van den Berg, B.
Eelkema, M.
Smith, M.
Van To, P.

Civil Engineering and Geosciences

Hydraulic Engineering

2006-03-24

Master project report. In the year 2004 there was a flooding in an area between Da'an River and Dajia River in Taichung County, Taiwan. The flooding was caused by outlets which were clogged up, thus lacking the capacity to discharge the amount of rainwater that the typhoon caused into the sea. A survey conducted by the project group, showed that the coastal protection is deteriorating, aging and inconsistent. Therefore the safety of the coastal protection is doubtful when extremely high water tables occur. The survey also showed that most of the outlets did not function properly, either they were clogged up, or the outlets were forced open by local inhabitants, using stones or tree-trunks. The main purpose of this project is to design a new coastal protection and drainage system, which will suffice in their main purpose, but are also sound with the ecological, recreational and spatial requirements. The alternative solutions consist out of three elements. These elements are the possibility of land reclamation, the possible methods of coastal protection and methods of drainage. There exists a strong relation between the elements. After the feasibility of land reclamation was considered, four categories of solutions concerning the coastal protection were treated: "do nothing", improvement or replacement of the current dike, offshore constructions and soft solutions. Concerning the drainage system the following categories are treated: allowing flooding (do-noting alternative), decrease of the peak discharge or structural enhancement of the capacity. It was concluded that land reclamation is a feasible option and has to be further elaborated because of the favorable conditions of the foreshore and opportunities for land use. By using a multi-criteria analysis a choice has been made out of the generated alternatives. This analysis has shown that dike improvement and/or the application of soft solutions are preferred for coastal protection. The use of detention and the removal of bottlenecks are the solutions selected for improvement of the drainage of the area. These alternatives are elaborated further. For land reclamation an area of 500 meters width and 2 km's length is selected at the south of the project area. The coastal stretch has been divided in four coastal protection zones. For each of these zones a design of the coastal protection has been made. The dimensions of the coastal protection of each zone are shown in table 1. The first zone is the land reclamation zone; because the shoreline at this zone is moved seaward the designed dike for this zone is considerably larger than the other dikes. The second zone is a zone with considerable foreshore vegetation. At this zone an ecologically sound dike has been designed with less steep slopes than the current dike and a grass revetment. Development of foreshore in this zone should be aimed at conservation by restricted use and natural development, but recreational opportunities for extensive recreation are available here. The third zone is a recreational zone, here a promenade is designed which is protected by a vertical front seawall. The fourth zone is a zone without foreshore vegetation, the dike designed for this zone is similar to the dike for the zone with foreshore vegetation only the revetment consists partly of placed blocks because the wave attenuating effect of the foreshore vegetation is not present.

Taiwan
river flood
coastal protection

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