here: ρ 1 = ρ s -ρ/ρ is relative ground density; ρ s and ρ is ground and water density. The solid particle density of bedload sediments varies within narrow limits, from 2600 to 2700 kg/m 3 (20). According to (1), upon receipt appears to be used mostly experiments **data** authors (21), in which experimental materials density were varied in a wide range from 1050 to 2650 kg/m 3 . If that the natural sediment density equals 2650 kg/m 3 , the lower escarpments angle calculated by the formula (1) will be equal to the constant value that does not correspond to a conclusion about the ridges' lower escarpments variability formed from natural sediment.