Suspended sediment input from crushed-stone ford construction on the Canadian Shield in Quebec

Abstract

Extensive and aging forest road systems, especially those that include poorly maintained stream crossings, can be significant sources of fine sediment that are detrimental to aquatic ecosystems. With limited resources available for culvert maintenance, alternative low-water crossings such as fords have been designed. Although crushed-stone fords have been used to minimize particle release during stream crossing, few studies have measured the fine sediment input that results from their construction. We used continuous turbidity monitoring paired with grab samples to obtain suspended sediment input from four construction sites with different streamflows, streambed gradients and bed and bank soil textures. Construction took place in the fall of 2018 and the summer of 2019. The results indicate that the suspended sediment load induced by the construction ranged between 72 and 831 kg. Sediment load appeared mainly sensitive to the fine particle content in the streambed and banks. We also observed that suspended sediment concentrations returned to background levels at every site within 2 h after construction. Compared with the failure of unmaintained culverts in which most road fill is washed into the stream, crushed-stone fords construction represent negligible sediment input. Our results suggest that improved fords could be an environmentally beneficial alternative to culverts on seldom-used roads where access is still required but resources for culvert maintenance are lacking.