Devan Fitzpatrick, Tanner Buggs, Timothy Stephens Roderick Lammers, and Brian Bledsoe, P.E
Bridge construction often requires placement of temporary features such as rock jetties and cofferdams in stream and river channels during the construction process. Environmental permitting agencies seek documentation, and in some cases quantification, of the potential effects of these temporary features on instream velocities and channel bank and bed scour; however, there is no existing guidance or standard method for evaluating the potential effects of these temporary construction features on hydraulics, bank stability, and biological habitats. This research improves the Georgia Department of Transportation’s ability to effectively respond to environmental permitting agency concerns about the potential geomorphic and hydraulic effects of temporary instream jetties associated with bridge construction practices. This report describes the development and application of new modeling and risk assessment tools for predicting average changes in velocity and shear stress in the contracted reach affected by a jetty using readily available information. The results can be used to determine the potential hydraulic and geomorphic effects of jetties prior to structure emplacement, and provides information about the spatial distributions of velocity and shear stress changes near jetties in areas of potential concern. This report also documents the development of a risk assessment that synthesizes 1-D and 2-D hydraulic modeling results and predictive regressions for shear stress and velocity into one comprehensive spreadsheet-based tool for predicting the potential hydraulic and geomorphic effects of jetties when more complex modeling is infeasible. This research can be applied to a large array of structures, including both temporary and semi-permanent in-stream unsubmerged structures, and advances the current set of tools available for preliminary structural design and environmental management decisions.
Describe the development and application of new modeling and risk assessment tools for predicting average changes in velocity and shear stress in the contracted reach affected by a jetty, to determine the potential hydraulic and geomorphic effects of jetties prior to structure emplacement.