Advanced Scour Monitoring at Indian River Inlet, Delaware

The scour holes threatening the bridge over Indian River Inlet, Delaware are unique in their size and location, and thus demand an innovative approach to their observation. Typical bridge scour occurs at the base of support structures. However, scour at Indian River Inlet has developed two large holes over 25m deep that flank the bridge. The deepest part of one hole sits just 45m away from the bridge foundation, and has been migrating toward the bridge at a rate that has alarmed Delaware Department of Transportation (DelDOT) engineers. Recently a real-time bridge and bathymetric monitoring system was installed, giving engineers the ability to make operational decisions regarding the safety of the bridge, and providing scientists a unique opportunity to investigate the coupled inlet morphologic evolution and hydrodynamics over multiple time scales. The monitoring system consists of two identical sets of instruments permanently mounted to subaqueous bridge piers, with one three dimensional imaging sonar and one horizontal ADCP comprising each pair. This new system represents significant progress in scour monitoring at Indian River Inlet. Previous efforts only provided snapshots of the storied evolution of the bathymetry or tidal forcing - and thus offered diminished potential for understanding the complicated inlet dynamics. Data from the instruments are automatically uploaded to University of Delaware servers and processed twice per day. Preliminary analysis of observed diurnal evolution in bathymetry along with associated forcing will be presented.