Spatiotemporal Investigation of Event-Driven Sedimentation in a Tidally Influenced Shipyard by Air and Waterborne Observations

Abstract

The tidally influenced shipyard Elsflether Werft, Germany, has experienced a large increase in siltation and short periods of refilling since the 2000s. Its navigational depth was reduced by over 2 m in 2017 and by 0.5 m within only 4 months in 2014. A comprehensive field study was conducted in 2016 employing a time-lapse camera, multiparameter probes, sediment traps, vessel-based measurements, and unmanned aerial observations. Measurements show a strong shear flow along the dock entrance, as well as distinct turbidity signal spikes during regular and neap tides, which are drowned during spring tides. Deploying an unmanned aerial system (UAS), sediment plumes entering the dock were observed. Introducing a biodegradable tracer into the dock, a vortex structure was monitored by the UAS and orthophoto sequences processed by particle image velocimetry yielding time-averaged surface flow patterns and magnitudes, which correlate well with other measurements. Contextual data revealed a cross-sectional widening and river-bed geometry changes, which indicate increased siltation rates attributable to a retention basin effect.