EVALUATION OF STREAM IMPROVEMENT PROJECTS 1930-1970

In the 1930s, after only three years of scientific investigation at the University of Michigan Institute for Fisheries Research, cheap labor and government-sponsored conservation projects spearheaded by the Civilian Conservation Corps allowed the widespread adoption of instream structures throughout the United States. During the 1940s, 1950s and 1960s, designs of instream structures remained essentially unchanged and their use continued. Despite a large investment in the construction of instream structures over these four decades, very few studies were ever undertaken to evaluate the impacts of the structures on the channel and its aquatic populations. The small number of studies that were undertaken to evaluate the impact of the structures often were flawed. Despite these facts, the use of habitat structures became an ‘accepted practice’ and early evaluation studies were used as ‘proof’ that the structures were beneficial to aquatic organisms. A reanalysis of evaluations of instream structures completed between 1930 and 1970 show that very little statistical evidence exists from this time period that the use of habitat structures benefited fish populations. Changes in stocking patterns, fishing pressure and fish migration create a large degree of uncertainty in many of the studies completed. Studies were also conducted for too short a time period to document long-term impacts on fish populations. Most evaluations that claim success of the project were conducted by the agency or individual responsible for implementation of the project, which raises concerns of objectivity. This concern is particularly critical given the fact that most project were publicly funded under the supervision of federal and state agencies, who were also ultimately responsible to demonstrate to the taxpayers the efficient use of these same funds. The literature review reveals that despite published claims to the contrary, little evidence of the successful use of instream structures to improve fish populations exists from the period 1930 to 1970. Given these facts, it is somewhat surprising that the use of instream structures developed as a standard technique used in channel restoration; an approach that continues today.