STREAM HABITAT HYDRAULICS - INTERANNUAL VARIABILITY IN 3 REACHES OF CATAMARAN BROOK, NEW-BRUNSWICK

The hydraulic habitat of 12 sites in a small salmon stream in central New Brunswick was investigated between 1992 and 1995 to determine patt erns of habitat (substrate) stability between and within reaches. Stab ility was evaluated by measuring particle size distribution in replica ted erosional and depositional sites in each reach and calculating the proportion of the bed predicted to be in motion at given flood flows. Erosional (riffle) sites in all reaches showed significant difference s (ANOVA, p < 0.05) in substrate particle sizes from year to year, mov ement of embedded sediment samplers, and high predicted bedload meveme nt, even in small spates. In contrast, depositional sites (flats, some runs) appeared stable, showing no significant year-to-year difference s in particle sizes, no movement of embedded samplers, and no increase in predicted bedload movement until high flow. The impact of the floo d on the streambed depends heavily on the particle size distribution p resent during the flood, resulting in different levels of substrate di sturbance during equal-magnitude floods in different years. Certain si tes (e.g., flats) may be able to serve as hydraulic refugia to stream fauna during some floods. It is clear that year-to-year variations in substrate stability must be considered when evaluating habitat stabili ty for stream fauna.