This research studies empirical equation for abrasion of stilling basin caused by impact of the sediment.
Review of previous papers shows that in previous researches, the mixture effect of erosion and impact are
studied without determination of the share of impact in the mixture effect. Also in the researches, the sediment
grain size is not as large as debris size in debris flow or experiments are done without tail water
depth. Therefore, in this research, the impact of large grain size is studied on concrete stilling basin with
tail water. First dimensional analysis is carried out, and subsequently experimental plan is designed. The
experiment includes concrete samples with three different cement contents, five depths of tail water, three
grain sizes. Abrasion of each grain impact is measured and recorded. Uni-variable and multivariable
regression analyses were employed to find possible relation between abrasion ratio and the dimensionless
parameter of the experiment. The empirical equations are judged using mean absolute relative errors of the
equations. Then a multivariable power equation is proposed for determination of the impacts of abrasion
of sediment. The equation shows the abrasion is function of dimensionless energy of sediment grain and
the ratio of the grain velocity on stilling basin to the grain velocity on water surface.