Numerical determination of residence time and age in a partially mixed estuary using three-dimensional hydrodynamic model |
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| Authors: | Wen-Cheng Liu Wei-Bo Chen Jan-Tai Kuo Chin Wu |
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| Institution: | 1. Department of Civil and Disaster Prevention Engineering, National United University, Miao-Li 36003, Taiwan;2. Taiwan Ocean Research Institute, National Applied Research Laboratories, Taipei 106, Taiwan;3. Department of Civil Engineering, National Taiwan University, Taipei 10617, Taiwan;4. Department of Civil and Environmental Engineering, University of Wisconsin-Madison, Madison, WI 53706, USA |
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| Abstract: | This paper documents a numerical modeling study to calculate the residence time and age of dissolved substances in a partially mixed estuary. A three-dimensional, time-dependent hydrodynamic model was established and applied to the Danshuei River estuarine system and adjacent coastal sea in Taiwan. The model showed good agreement with observations of surface elevation, tidal currents and salinity made in 2002. The model was then applied to calculate the residence time and age distribution response to different freshwater discharges with and without density-induced circulations in the Danshuei River estuarine system. Regression analysis of model results reveals that an exponential equation can be used to correlate the residence time to change of freshwater input. The simulated results show it takes approximately 10, 4.5, and 3 days, respectively, for a water parcel that has entered the headwaters of the estuary to be transported out of the estuary under low, mean, and high flow conditions with density-induced circulation. The calculated age with density-induced circulation is less than that without density-induced circulation. The age of the surface layer is less than that at the bottom layer. Overall the study shows that freshwater discharges are the important factors in controlling the transport of dissolved substances in the Danshuei River estuarine system. |
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| Keywords: | Residence time Age Three-dimensional hydrodynamic model SELFE Salinity Danshuei River estuary Freshwater discharge |
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