vee liikumist takistavad voolusängi ebatasasused, неровности речного русла (отмели, рябь, антидюны, искривление русла), оказывающие сопротивление движению воды, the relief at the base of a flowing fluid, which comprises the bedforms (or form roughness) and the projections fromthe sediment bottom(or grain roughness) and which represents the frictional effect that the bed exerts on fluid flow