Gabion weirs or drop structures are classified into three types, that is, vertical, stepped and sloped according to the shape of their downstream face at the center of flow. Gabion weir structures are used when there is a sudden change in river bed levels or on steep gradients in water courses to reduce water velocity. The weir is effectively a gabion dam which allows water to flow over the crest controlled by introducing a notch that can be rectangular or other shapes.
The water can flow over the notch to a lower bed level. The weir is designed as a retaining structure with an apron protection to prevent erosion of the bed. In instances where there are high flows over the weir, it may require a stilling pool to be included in the design generally with an additional counter weir.