| Summary: | Currently, stream restoration activities in British Columbia emphasise the use of large woody
debris (LWD), boulder, and other habitat structures (Slaney and Zaldokas 1997). The purpose of
these works is to create locally varied hydraulic conditions; promote scour and pool formation;
and create low velocity refuges. Little work, however, has been done to characterize the changes
to local flow hydraulics, morphology and in stream habitat that results from these efforts.
This study provides a methodology, through the use of field surveys and 2-dimensional
hydrodynamic modelling, to assess morphological and hydraulic effects of instream LWD and
boulder structures. Changes in available fish habitat were quantified through the use of Bovee
(1978) probability-of-use curves. The selected field study site is a side channel of the Chilliwack
River. Instream structures, installed in the summer of 1999, were subjected to a bankfull flow
event that caused significant scour and bed morphology change. Results indicate that pool area
increased by 50% due to the hydraulic effects of the instream structures. Two-dimensional flow
model velocity and depth predictions compare favourably to recorded field values, while the
predicted shear stresses, derived from the model's output, coincide reasonably with the newly
formed pool locations. Pre- and post-restoration differences in fish habitat were quantified for a
range of discharges using the weighted usable area (WUA) method (Bovee 1982). This analysis
determined that the greatest benefit offered by the instream restoration structures was in
supplying low velocity refuge areas during high flow events. === Applied Science, Faculty of === Civil Engineering, Department of === Graduate
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