Aeration to high-velocity water flow is an effective measure to reduce cavitation damage. However

under the condition of mild chute bottom slopes and large variations in reservoir stage

a conventional aerator is usually difficult to form stable

water-free aeration cavities. This paper examines the flow characteristics and aeration effects of bottom aerators through model tests under the condition of a mild bottom slope (3.3%)

and compares conventional continuous aerators

special-shaped aerators

and combined aerators. We find that three main factors－Fr number

aerator slope

and chute bottom slope at the water nappe landing point－affect the incidence angle of water flow. At the chute bottom slopes tested

the influence of variations in aerator size is much greater than that of shape change; it is difficult to effectively solve the problem of water accumulation in the aeration cavity if a special-shaped aerator is adopted. Based on our scale model tests of a real project

we have shown that the combined sill aerator creates good air flow patterns

and it is applicable to the working heads with large amplitudes and better controlling backflow water in the cavity on mild bottom slopes.