Project Code:	WELD-01-018
Sponsor:	Weldwood of Canada Ltd.

Sediment intrusion into streambed gravel can affect fish populations by suffocating fish eggs, hindering the removal of metabolic wastes, and preventing newly hatched fish from emerging. In addition, excess sediment can change channel morphology, and decrease habitat for overwintering, food availability, and spawning success. The primary objective of this study was to determine whether there was more fine sediment downstream of stream crossings than upstream of first to third order streams in the foothills of west-central Alberta.

The study area is located in the Hinton-Edson foothill region of west-central Alberta. In 1995 and 1996, 15 gravel-bottomed streams with similar channel sections upstream and downstream of crossings were sampled. The streambed substrate near the bridges or culverts were examined and sampled for sediment intrusion. To keep the samples within a reasonable distance from stream crossings, a zone of influence was identified. Downstream samples were taken within this zone of influence, while upstream samples were taken outside the influence of the crossing. The streambed material was sampled in September and October of the respective years using the freeze core method, a technique whereby streambed substrate is frozen to a probe and then extracted for analysis.

Particles less than two mm in diameter including silt, clay, and to a lesser degree sand have been found to influence rainbow trout embryo survival. The study found that narrow streams had a significantly greater amount of this fine sediment downstream than upstream, and a generally greater amount of fine sediment overall than wide streams. Both wide and narrow streams on average were also found to have a greater amount of sand, silt and clay downstream than upstream in both sample years. All of the streams sampled had a greater amount of fine sediment present than what is desirable for developing embryonic fish in sections upstream and downstream of crossings.