Evaluation of Pool Habitat Suitability of In-Stream Structures in Restored Streams of Western North Carolina

Abstract Evaluation of Pool Habitat Suitability of In-Stream Structures in Restored Streams of Western North Carolina by Amy Hammontree August 2007

One of the most critical aspects of stream restoration is the creation of suitable aquatic habitat. Much of this work is accomplished through the installation of both hard and soft in-stream structures. The structural stability of these practices has been well studied and monitored for decades. However, the evaluation of habitat potential of these structures has remained almost entirely qualitative and categorical. The objective of this study aimed to fill this void by quantitatively evaluating the habitat potential of a variety of common in-stream restoration structures and bend treatments in Western North Carolina through the measurement of common habitat features such as pool depth and length, distance to cover, and depth of cover (or undercut), with the ultimate goal of providing design recommendations for stream restoration projects listing habitat enhancement as a top priority. In analyzing the results of the study, high habitat quality was defined by large pool depths (for increased niche space and low flow velocities), small distances to cover, (for faster escape from predation), and large cover depth or undercut values, (for shelter, predation, and rearing). Collectively, soft structures provided the deepest pool depths, with shorter distances to cover and larger cover depth values than corresponding hard in-stream structures. Likewise, bend treatment groups containing soft in-stream structures also excelled in these areas. Bends containing hard structures produced much higher pool lengths, in many cases longer than the curvature of the bend itself. Design goals based on habitat enhancement of small streams should focus heavily on the installation of rootwad revetments and cover logs for creation of deeper pools with increased flow variation and increased cover depth. In addition, both these structures will also serve to promote the acquirement and continued recruitment of large and small woody debris into the streams. Where hardened structures are deemed necessary for structural or hydrologic purposes, they should be accompanied by soft in-stream structures to create combination bends to supplement habitat within these areas.