A CENTURY OF INSTREAM STRUCTURES: 1880S TO ROSGEN

The value of instream structures has never been demonstrated with enough scientific merit to justify their current widespread use. Beginning in the 1880s, engineered devices were used to modify river environments in the U.S. The approach became institutionalized by the 1930s with academic and federal involvement. A number of similarities exist between the practices established in the 1930s and the Natural Channel Design method developed more recently by Dave Rosgen. In the 1930s, federal government practitioners learned methods to install instream structures in a series of week-long training sessions, and then headed to numerous sites across the country to supervise crews of workers. Although 1930s-era project designers claimed a scientific management approach, projects were rarely studied, and lacked data collection and hypothesis testing fundamental to the scientific method. Today, practitioners learn methods in short courses, and often describe projects as experimental despite the lack of requisite hypothesis testing. Restoration projects in the 1930s relied heavily on an aesthetic appeal of geometric structures that reflected a desire to bring order to natural systems. Several specific designs proposed for use in the last decades are completely unchanged or similar to those of 1930s. Other modern designs now depend on more rounded features and natural materials as part of a new aesthetic valuation that hide the underlying structure. However, the newer natural appearance does not ensure successful incorporation of natural process. Unfortunately, static instream structures designed to prevent natural channel change ignore the long-term sustainability of ecosystem function dependent on erosional and depositional patterns. Structures that prevent dynamic changes limit a river’s ability to recruit wood and scour out embedded channel-bed substrate. A literature review of large multi-project evaluations of restoration projects that utilize instream structures reveals little evidence for positive ecological benefits associated with the use of these devises. A new effort focused on independent monitoring and evaluation of every restoration project is needed to ensure that all projects feed our scientific understanding to avoid the pitfalls of our past failures.