The present study aimed to investigate the effect of gabion structures with different lengths and heights in the downstream vertical drop on the energy dissipation values, relative depth, and downstream Froude number. Experiments were performed, for a simple vertical drop and a Gabion with two heights of 15 and 20 cm, Gabion structures with three relative heights (hd,13hd,23hd), four relative lengths (hd,2hd,3hd,4hd) and porosity 50%. The hydraulic parameters obtained from the present study were compared to the results of a simple vertical drop. Based on experimental observations, inflow, transient, flow, and overflow were observed when the flow passed through the Gabion vertical drop models. Reducing the height of the Gabion structure and making it a step causes a pool area on the Gabion structure and reduces energy dissipation. For a constant relative length, as the relative height of the Gabion structure increases, the contact of the passing flow through the porous medium increases which leads to an increase in the energy dissipation of the flow. For a constant relative height of the Gabion, increasing the relative length of the gabion structure has little effect on the value of energy dissipation. The results showed that in all laboratory models, on average, the gabion structure caused a higher energy dissipation of the flow, (56%) compared to the simple vertical drop. The Froude number range was reduced from 3.8–5.7 to 0.41–2.65 with a gabion structure in the simple vertical drop.
