Abstract
Steep slope types of revetment are commonly used in Japan as a countermeasure intending to reduce flood damage in small-and-medium-sized rivers to expedite their improvement works and to save land cost. In result, cross-sectional shapes become narrow and deep, frequently causing severe destruction of channels in spite of the improvement. It follows local bed scours around change points in channel forms caused mainly by accelerated flow due to reduced channel roughness by the improvement. This paper presents a consideration on the reasons why cross-sections of small-and-medium-sized rivers in Japan had been changed into narrow trapezoidal shapes with steep side slopes according to historical changes of technical criteria in river improvement schemes, along with that on the difference of channel roughness determination among several technical criteria.
