Relationship between Large Woody Debris Characteristics and Pool Formation in Small Coastal British Columbia Streams

Abstract

Abstract The characteristics and function of large woody debris (LWD) were measured in 41 small (1.2-11.2-m bank-full channel width), fish-bearing streams in coastal British Columbia to determine how total LWD abundance and the features of individual LWD pieces (diameter, length, orientation, and presence of a rootwad) influenced the effectiveness of pool formation. Pool spacing (the number of channel widths between channel-spanning pools) was a decreasing power function of total LWD abundance, but the relationship was relatively weak. Stratification of sites by channel gradient improved the model fit, steeper streams (≥2% gradient) having a significantly lower pool spacing than lower-gradient streams (<2%). The proportion of LWD that formed pools increased from 6% for pieces with a diameter of 15-30 cm to 43% for pieces with a diameter of more than 60 cm. Large woody debris more than 60 cm in diameter formed a higher proportion of pools across all channel widths. A simple, size-structured model of LWD ab...