The tidal bore in the Sittaung River
Author
de Ridder, M.P.
Contributors
Wang, Z.B. (mentor)
Rutten, M.M. (mentor)
Delft University of Technology
Abstracts
A 2Dnumericalmodel is set-up for the tidal bore in the Sittaung River. This model is used to analyse the effect of the bottom friction, bathymetry, tidal range and river discharge on the propagation of the tidal bore. To obtain information about the tidal bore the Sittaung River is visited two times. During the second visit, depth measurements were carried out. It became clear that the tidal bore occurs only a few days after full and new moon at the village Kyaik Ka Thar. The tidal bore is also observed near Kyaik Ka Thar as an undular bore with a height of ± 0.3 m. Downstream in the estuary the tidal bore is larger and occurs 5 till 7 days after full and new moon. A numerical model is set-up for the region from Madauk till the Gulf of Marteban. The bathymetry is based on various datasets. Only a few cross-sectional profiles were available for the upper part of the model. The SRTMmap was used to determine the bottom slope of the river, whereas the cross-sections were used to determine the cross-sectional profile. From the depth measurements the initial depth for the bottom slope was obtained. The Navioncs webapp is used for the lower part of the domain (Gulf of Martaban). Both parts of the bathymetry were connected by using linear interpolation. From the Landat pictures the locations of the intertidal areas were obtained. As an upstream boundary a river discharge is set. A tidal signal is used as the downstream boundary. This downstream signal consists of two components: a daily double high water signal (D2) and a daily quarter high water signal (D4). The calibration is based on the propagation of the tidal bore. When the water level changes are larger than 0.2 m within 2.5 minute it is assumed that the tidal bore has propagate through a grid cell. On this way, the model results could be calibrated with data obtained from the field. For verification the relation between the cross-sectional area and the tidal prism was checked. For the sensitivity analyse the bottom friction, tidal range, bathymetry and river discharge were varied in various simulations. From these results can be concluded that the river discharge has no influence on the tidal bore, whereas the other parameters has a significant effect on the tidal bore. This implies that damming the Sittaung River, resulting in a change of the discharge, will not affect the tidal bore. Thus, changes of the propagation are only caused by the geometry and bathymetry of the estuary. Secondly the variety of the tidal bore is only caused by the tidal range, because this is the only parameter which change throughout the year. At least the effect of the tidal bore on the erosion is checked, but it is very difficult to relate the tidal bore to the erosion due to the lack of data. Upstream in the estuary the tidal bore is a small undular bore, which will not cause must erosion. Downstream of the estuary the tidal bore is larger and could have much more effect on the erosion.
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