Hydrodynamic Conditions Surrounding Brown Trout and Rainbow Trout Redds

This study examines the hydrodynamic properties of river spawning fish nests commonly referred to as redd's. Little is known about the hydrodynamic properties, spatial location preference and persistence of such structures, relative to flow complexity and channel morphology under varying flood conditions. Many biological studies and inventories of brown Trout (salmo trutta) and rainbow trout (Oncorhynchus mykiss) have been conducted which identify that redd's are typically found in riffle and run morphologies of gravel bed streams, however, the site specific fluid and sedimentological properties of fish staging locations and nest persistence remain unknown. An approximate 1Km reach of Whitemans Creek in Southern Ontario, Canada has been studied in great detail to elucidate the hydrodynamic properties of redd's immediately after spawning has taken place and throughout a series of higher discharge events while the ova remain in the nests. A Pulse Coherent Acoustic Doppler Profiler (PCADP) was used in conjunction with a 20 cm square sampling grid suspended above a series of redd's, in a non-invasive manner, to measure the boundary layer shear and three dimensional velocity profiles within the limits of each redd and the surrounding region. Three-dimensional velocity profiles have been constructed at each redd which spatially range between 20 – 50 discrete velocity profiles being measured within each nest. Scour chains were installed and pavement samples collected in the region surrounding each redd to characterize the sediment transport processes and tractive force conditions of the channel bed proximal to each redd location. Results are presented for the fall 2006 brown trout run and the spring 2007 rainbow trout run.