◇ When tide water enters the coastal river with high tidal range, the seaward flow of the river obstructs the incoming tide, with the result the front of tidal wave crest is forced to assume high tidal range. Thus, the tidal wave with steep tidal wall of more than 5 m in height rushes upstream or up bay. This wall-like high tidal waves are called tidal bores which move upstream with average speed of 20-22 kilometres per hour.
□ The following conditions are conducive for the occurrence of tidal bore: –
◇ Narrow and low-lying coastal river with gentle channel gradient,
◇ A bay with narrow opening and tapering head,
◇ Large tidal range (wave height), usually more than 5 meters,
◇ Upward decreasing water depth, meaning thereby decreasing depth of water in upriver section, etc.