CHANNEL RESTORATION USING INSTREAM STRUCTURES: HISTORICAL DEVELOPMENTS AND LIMITATIONS

The use of instream structures to improve aquatic habitat has a long history in the United States with the first published use of instream structures in New York during the 1800s. Evidence of early structures can still be found along the Beaverkill River, New York demonstrating the potential for long-term impacts. In the 1930s, after only three years of scientific investigation, cheap labor and government-sponsored conservation projects spearheaded by the Civilian Conservation Corps allowed the widespread adoption of instream structures. World War II temporarily ended the government conservation efforts and prevented the evaluation of structures installed. During the 1940s, 1950s and 1960s, designs of instream structures remained essentially unchanged. Meanwhile, the few studies that were undertaken to evaluate the impact of the structures often were flawed. The Blackledge River, Connecticut provides a good illustration of the historic problems with channel-restoration using instream structures. This river was the first site for scientific investigation of the impact of instream structures on fish populations. Remarkably, some of the 1930s-era structures still survive today in various stages of decay. A case study was undertaken to determine the current state and geomorphic impact of habitat improvement activities after almost 60 years of existence. Tree recruitment along riprap revetments and cover structures was retarded leading to less undercut habitat than along undisturbed reaches. Even where structures remain, traditional restoration techniques do not replicate natural channel processes and often fail to create the improvements envisioned by restoration designers. Deficiencies in the beneficial impacts of the historic restoration efforts are not primarily due to a failure to follow acceptable designs practices, but in the inadequacies of the designs themselves. As the case study highlights, there were few advances in the use of instream structures since the 1930’s and the structures are of questionable benefit to the channel.