On the Rollwave-Trains Appearing in the Water Flow on a Steep Slope Surface

Abstract

When we carefully observe a thin sheet flow with a suitable depth on a surface or in a channel of which the slope is greater than about 2%, we can see small continuous wave-trains moving to the down-stream with a uniform wavelength. For instance, we often find them on a road surface with a steep slope in a heavy rain, and the wave-trains in a thin sheet flow of rain-wat.er are called “rain wave-trains”. These wave-trains are rollwaves with a wave-height of several times the mean water depth and it is said that they have a close connection with the soil erosion, but researches on such wave-trains are few and unsatisfactory. In this paper, in order to obtain a foothold necessary to study the relations between the soil erosion and these rollwave-trains from the point of view .of civil and agricultural engineering, the hydraulic properties of the wave-trains are researched theoretically and experimentally by the wooden flume with a smooth bed. At first. a criterion in which the rollwave-trains begin to appear is determined, and then the various properties of the wave-trains, i.e. period, wave-length and .wave-velocity etc. are ascertained by using an electromagnetic oscillograph or a cathoderay oscilloscope and recording the wave-profile.