Interest in stream restoration has increased over the last two decades, leading to a growth in the industry to the point that it has become a 1 billion dollar per year enterprise (Bernhart et al 2005, Thompson 2002). In north-central Pennsylvania alone, over $9 million has been spent since 1999 on stream restoration projects, from the designing stage to actual construction and reconstruction of the sites. Even though a extensive amount of money is being spent on the construction of these projects, very little to no post-monitoring is taking place. Without post-monitoring of the projects, it is unknown if they actually work.
After a successful statewide stream restoration assessment was completed in North Carolina by the advisor of this project, it was discussed to undertake a similar one for the state of Pennsylvania starting with the north-central region. This includes Bradford, Cambria, Cameron, Centre, Columbia, Lycoming, McKean, Montour, Northumberland, Potter, Sullivan, Tioga, and Union Counties. Within these 13 counties over 60 restoration projects have been implemented since the 1990s ranging in type from FGM structures to Fish and Boat Commission habitat structures. Twenty-two of the restoration sites comprising of 58,255 feet of restoration work were selected for individual site assessment during March 2008-May 2009. Over 300 structures were assessed during this period of time for structural integrity and the degree to which the adjacent bed and banks had been affected by unintended erosion or deposition.
Approximately 75% of the structures have sustained some structural damage (ranking >1) or erosion or deposition (ranking >1). Thirty-five percent of the structures have sustained significant damage (ranking >2) or significant erosion or deposition (ranking >3). Most of the damage (63% of all structures) is related to erosion or deposition which can impact the functionality of the structure. Many of the streams in north-central Pennsylvania are experiencing pulses of aggradation of gravel-cobble size clasts throughout the stream system. This pulse of gravel is contributing to the partial burial of individual structures and may fill in the pool that was created by the structure. Out of the four highly used structure types (cross vanes, j-hooks, log vanes, and rock vanes), j-hooks and rock vanes sustained the highest percentage of damage compared to the other two structures. Much more work needs to be completed in this region before we can fully grasp an understanding for failure of the various structures.
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Geology & Environmental Geosciences