This article delves into the crucial intersection of two aspects of sustainable engineering: achieving design aims, and not worsening the quality of the surrounding environment, focusing on the impact of the downstream concrete reinforcement length on the amount of local and secular erosion. In practice, the downstream weir reinforcement is often designed assuming the division into rigid and flexible parts. Rigid fortifications are usually concrete slabs laid with their longer edge in accordance with the direction of water flow. Flexible fortifications, on the other hand, can be made using aggregates and natural stones. The literature review demonstrates that local scours cannot be completely excluded. Therefore, it is important to predict their location and geometric dimensions already at the design stage. After exceeding a certain length of reinforcements, the effect of their length on the magnitude of local scour becomes insignificant. Thus, lengthening the concrete slab does not have the desired effect and only translates into an increase in their volume and therefore cost. The approach involves investigating the relationship between the length of rigid reinforcement at tailwater part of a laboratory weir model on the length and depth of local scours. The conclusions obtained from this research can contribute to the development of environmentally friendly and sustainable engineering practices, ensuring the longevity and environmental friendliness of hydraulic structures.