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Civil-Comp Proceedings
ISSN 1759-3433
CCP: 81
Edited by: B.H.V. Topping
Paper 86

Interaction between Physical, Chemical and Biological Processes in the Coastal Water off a River Mouth in a Post-Flood Condition

Y.M. Yustiani+ and A. Mano*

+Environmental Engineering Department, Pasundan University, Bandung, Indonesia
*Disaster Control Research Center, Tohoku University, Sendai, Japan

Full Bibliographic Reference for this paper
Y.M. Yustiani, A. Mano, "Interaction between Physical, Chemical and Biological Processes in the Coastal Water off a River Mouth in a Post-Flood Condition", in B.H.V. Topping, (Editor), "Proceedings of the Tenth International Conference on Civil, Structural and Environmental Engineering Computing", Civil-Comp Press, Stirlingshire, UK, Paper 86, 2005. doi:10.4203/ccp.81.86
Keywords: leaching, particulate nutrient, eutrophication, sediment, Princeton Ocean Model, coastal waters.

A heavy load of land-based nutrients contained in the flood, mainly as particulate form cannot be utilized directly by biota. As the consequence, the particulate nutrients will be settled down in the sediment. Thus, a high concentration of dissolved inorganic and organic nutrients will be leached from the sediment into the overlying water.

The condition of dissolved-nutrient-rich water can stimulate the overgrowth of plankton in the water column. A high activity of decomposition consumes much oxygen especially in the sediment, and the overlying water. Low oxygen gives uncomfortable condition for biota to live in, which will increase the mortality rate. Death biota decomposition will again use oxygen for the process and consequently will generate the septic and eutrophic condition in the overlying water. In this study, an integrated 3-D model, which represents the above phenomenon was developed considering some interactions between the physical, chemical and biological processes.

The coastal waters off the Abukuma River Mouth were selected for the research location as it has the records of high flood. The Princeton Ocean Model [1] was used as the basic computation of the hydrodynamic simulation. It employs the sigma coordinate system for the vertical gridding. The ecological concept of the nutrient model was adopted from previous research [2]. The concept was modified to clarify the settling and leaching processes, which were importantly involved in supporting the phenomenon mentioned above. Oxygen consumption by the decomposition of organic matter contained in the sediment is also an important mechanism to stimulate the leaching process.

The validation process for the model was conducted by using the field data. The computation outputs show that agreements were achieved between field survey data and simulation result. Although some discrepancies appeared, the phenomenon was clearly presented. The particulate forms of the nutrients were dominating the bottom layer, which cause the decrease in the oxygen concentration. The computation results show that approximately 15-25% of the settled nitrogen and 5-11% settled phosphorus were leached into the water column within 15 days in the first stage after the flood event.

The model developed was successful in presenting the phenomena that occurred in the coastal waters off the river mouth after the flood events. It is possible to have more clear direction toward monitoring of the nutrient-enrichment in the coastal region.

Blumberg, A.F., Mellor, G.L. "A description of a three-dimensional coastal ocean circulation model". Coast. Estuar. Sci. 4, (1987) pp. 1-4 In: Three-dimensional Coastal Ocean Model, N.S. Heaps (Ed.)
Yanagi, T. Coastal Oceanography. Terra Scientific Publising Company, Tokyo, Kluwer Academic Publishers. (1999) pp. 1-162.

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