Modeling water exchange in Cigu lagoon, Taiwan

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Ting-Chieh Lin, Shih-Chun Hsiao, Chih-Min Hsieh, Pengzhi Lin

Wednesday 1 july 2015

12:36 - 12:39h at Asia (level 0)

Themes: (T) Hydro-environment, (ST) Impacts of pollutants on the water environment, Poster pitches

Parallel session: Poster pitches: 9G. Environment - Impact

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Cigu lagoon is the largest lagoon ecosystem on the southwestern coast of Taiwan. Geographically, a visible feature nearby Cigu lagoon is that there are three spectacular offshore sandbars nearly parallel to the coastline. The water exchange between lagoon and open sea mainly relies on two narrow inlets between three sandbars. The sandbars are very important because that they are natural shields to prevent whole lagoon from being attacked by typhoon/incident waves. The formation of sandbars has been believed to be an accumulative effect seeding by sedimentation from Zhengwen river in the southern of lagoon during the past decades. However, our recent field investigations particularly on sandbar morphology (shape and bathymetry) indicate two important changes: (1)three sandbars have been migrating toward inner lagoon; the northern and middle lagoons were also found to integrate into a large one. (2)wetlands and water depths in lagoon were therefore became smaller and shallower, respectively. In this article, a two-dimensional depth-integrated hydrodynamic model and a solute transport model are developed to model water exchange between Cigu lagoon and open sea. The main attention shall paid to morphological effects of sandbar migration versus water exchange in lagoon. The Local Residence Time (LRT) is applied to be an identifier for quantitatively assessing water exchange capability. The up-to-date tidal velocity, tidal gauge and lagoon bathymetry are reported to develop a well-defined numerical environment to the present topic. Reviewers who are interested in Cigu lagoon please visit given hyperlink for a preliminary view. https://dl.dropboxusercontent.com/u/9411025/2015_IAHR_Cigu%20lagoon%20map.pdf