Author(s): Ken-Ichi Hirayama
Linked Author(s):
Keywords: No Keywords
Abstract: Design of channels in cold regions requires better understandings of an ice covered stream, such as the knowledge of hydraulic resistance of the ice cover and a method to evaluate a composite roughness coefficient for a section. However literature about ice roughness, for example, still indicates a wide variety of the ice resistance from hydraulically smooth to a case which is almost as large as for natural river beds. Hence to obtain more definite information, five years field investigation was planned and performed in Hokkaido. Based on the measurements this paper describes several hydraulic features of ice-covered streams; after a process of ice cover formation Is explained, from observations of vertical movements of the cover it is concluded that an ice cover is floating on the surface of water and covered this channel flow has a pressure equal, to a weight of the ice cover. Then Manning's roughness coefficients for the cover are computed from measured velocity distribution and grouped in accordance with ice conditions as a flat and smooth ice cover, rippled ice cover, a cover with frazil ice flowing or accumulating under the cover. And a magnitude of the coefficient for each of these cases is obtained. An analytical formula for evaluating the composite roughness is also proposed and the idea to derive this formula is tested satisfactorily by comparing a theoretical relationship for a position of relative depth of the maximum velocity and a ratio of roughness coefficients for river bed and ice cover with results measured in the fields.
Year: 1981