Temporal and Spatial Quantification of Fine-Sediment Accumulation Downstream of Culverts in Brook Trout Habitat

Abstract

We quantified fine-sediment accumulation annually from 2000 to 2003 after culvert construction in five Laurentian Shield streams containing brook trout Salvelinus fontinalis. A significant spatial pattern (section effect) was observed in which the accumulation was lowest upstream of the culvert (section 1), peaked in the section directly below the culvert (section 2), and slightly decreased in sections further downstream (sections 3-5) without returning to upstream levels. The accumulation was always significantly higher downstream of the culvert than in section 1. The temporal pattern (period effect) was also significant; accumulation was lowest several weeks after construction, peaked at one full year after construction, and decreased at 2-3 years postconstruction. Fine-sediment accumulation differed significantly among all periods. The downstream distance at which sediment accumulation returned to upstream levels varied from 358 and 1,442 m below the culvert. Owing to the accumulated sediment, which probably originates primarily from construction sand or road erosion, habitat downstream of a culvert is in many cases of lower quality for brook trout incubation and rearing. Recommendations for minimizing culvert impacts on fish habitat are discussed.