A major TRRP focus is to provide for habitat and channel complexity via fluvial process restoration. It has been assumed that appropriate microhabitat features will then evolve as fluvial processes are restored. However, not as much attention has been paid to specific microhabitat features and habitat complexity.
The TRRP built four mechanical riverine restoration projects located between river mile 73 and 78 in fall 2006. As originally designed, these sites included long sections of bank excavation in order to remove process-impeding riverine berms (along with associated riparian trees) that have formed under reduced flows. Removal of these trees eliminates a valuable resource. It is widely acknowledged in this ecoregion that large woody debris derived from riparian trees (LWD) interacts with water and sediment to create channel complexity and is an important component of aquatic habitat. LWD also provides roughness elements that promote fluvial and topographic complexity, patchiness, hydraulic variability, and local scour and fill. Thus, salvaged LWD was incorporated into parts of these project sites during construction, while berms were removed as planned.
We are evaluating the impact of adding this LWD by quantifying the increase in reach level LWD loading, assessing the stability and persistence of different types of LWD installations, observing fish use of habitats with and without LWD, and surveying habitat and channel complexity as the sites evolve. Preliminary results indicate that LWD loading has been increased by over 40%, fish are preferentially using habitats incorporating LWD, most of the installations are stable, and sites demonstrate fluvial complexity.
