Water Resources Research Act Program

Details for Project ID 2008OH76B

Observations of River Topography and Flow Around Bridges

Institute: Ohio
Year Established: 2008 Start Date: 2008-03-01 End Date: 2009-02-28
Total Federal Funds: $32,391 Total Non-Federal Funds: $64,793

Principal Investigators: Thomas Lippmann

Project Summary: The scour around bridge foundations is the leading cause of bridge failure in the United States. Unfortunately, our present understanding of flow and sediment transport near structures limits accurate prediction of the geomorphology around bridge piles. The overriding limiting factor is the lack of detailed observation of river flow and riverbed topographic evolution in the immediate vicinity of the bridge structure. This problem is exacerbated by reliance of mobile survey systems on GPS-based positioning which can be compromised around large overhead structures. Although highly accurate when a clear view of the sky allows at least 5 GPS satellites to be locked on, obstruction by the bridge itself renders the survey data inaccurate and thus the subsequent topgraphic or flow data unusable. For short, periodic losses of satellite lock, the data can be interpolated with reasonable accuracy. However, in the vicinity of the bridge, the drop-outs are generally substantial and require a finite time period to re-acquire the satellite grid (which can take up to a minute or so). This is particularly damaging when considering that the highest flow variability and topographic irregularity is in the vicinity of the bridge itself. In this research, we will develop methods to conduct accurate topographic and hydrographic surveys beneath bridges. We will utilize an in-hand state-of-the-art hydrographic and bathymetric survey system to conduct the surveys. The methods are based on GPS positioning when satellites are locked on, and on operator consistency and projected paths and speeds between loss and lock of the GPS satellite grid. The techniques developed will allow observations of the flow and topography around Ohio bridges to be made rapidly and accurately, and thus used to evaluate flow-structure interactions and make inferences as to the risk of the bridge structure to scour-related failure.