| Measurement of river discharge is the most important works for river management. This is conducted also in tidal regions. The hydraulic condition in the tidal region is decided by tidal waves and river discharge. It seems that the phenomenon becomes more complicated when water surface is covered by ice. However、 the hydraulic phenomenon of ice-covered rivers in the tidal region has not been clarified by the difficulty of field measurements. For this reason、 in the ice-covered rivers of winter、 the observation of discharge is performed by the observation method of a summer season as a matter of convenience. Therefore、 it is said that the accuracy of the discharge in winter season is not satisfactory.[*][*]The aim of this study is to understand the hydraulic conditions of ice-covered river in the tidal region by field measurements. The hydraulic characteristics are examined on the basis of field observation data. Tokoro River is selected as a survey site. In 2005、 observations were conducted in both ice-covered and open-water conditions. The observations were performed at the time of the monthly highest tide. Flow velocity and salinity distributions at a cross-section、 water levels and gradients of water surface were continuously observed. The 3-D flow velocity measurement used ADCP.[*][*]In this study、 the main hydraulic phenomenon as follows became clear.[*][*]・Phenomenon thought to be unrelated to ice-sheet[*]1. The stream centerline shifts according to the tide direction.[*]2. The maximum flow velocity of salt water is appeared at near the boundary between salt water and fresh water.[*][*]・Phenomenon thought to be related to ice-sheet[*]1. Behavior at horizontal flow velocity caused by meandering of river course. |
