Assessment of harbor oscillations and ship waves for mariners’ safety –Collaboration (June 19 – July 28, 2016)
Theme：Mariners’ safety, harbor oscillations, ship waves, numerical modeling.
Location: Université de Pau et des Pays de l’Adour, Anglet, France
Leibniz Universität Hannover, Hannover, Germany

The effects of sea-level rise and storm intensification pose a combined engineering and socialeconomic problem to coastal communities around the world. Especially, ports and harbors arechallenged by long-period oscillations triggered by swell waves and basin resonance. At the sametime, an increasing global market forces these facilities to ensure safe and timely operations.
Assistant Prof. Volker Roeber (International Research Institute of Disaster Science (IRIDeS),Tohoku University) and Associate Prof. Denis Morichon (Université de Pau et des Pays de l’Adour)
have been investigating harbor oscillations in the Port of Bayonne (SW France). The Port ofBayonne is a natural harbor at the mouth of the Adour River. It is mainly being used by bulk
cargo vessels to support a local steel refining factory as well as by fishing and recreationalboats. The harbor entrance faces the open Atlantic Ocean and is partially sheltered by two
breakwaters. However, large winter swells are known to cause substantial oscillations incombinations with strong flow velocities in the entire harbor and upstream in the Adour river.
Snapped mooring lines, drifting vessels, and shutdown of operations are common problems
during these events. In addition, the discharge of the Adour River is transporting large amountsof sediments downstream. The longshore drift, interrupted by the breakwaters, contributes tothe sediment accretion near the harbor entrance that requires regular dredging operations.
The collaborative study has been focusing on the numerical computation of the local wave
conditions and subsequent harbor oscillations. We found that during large winter swell events
long-period infragravity waves are released from breaking swell waves right in front of theharbor entrance where a sill of dumped dredging material acts as a focal point for the localwaves. Part of the IG spectrum experiences resonance due to the harbor’s geometry. The
mean flow velocity in the area where vessels are moored can quickly exceed 1 m/s andprovides an explanation for the mooring problems reported by the port authority (lamanage).
In addition, a collaborative study with the hydraulics and coastal engineering laboratory ofProf. Torsten Schlurmann (Leibniz Universität, Hannover, Germany) has shown that ship waves
can be accurately computed with depth-averaged equations such as used for storm waves ortsunamis. Especially the propagation and interaction with waterway embankments and harbors canbe accurately computed with simple geometries of moving pressure disturbances does and does
not require the detailed computation of fluid-body (ship hull) interaction. A manuscript, submitted
to Coastal Engineering, is currently under revision.

Flow speed generated by storm waves
around Port of Bayonne.

Ship waves near a waterway embankment

Prepared by: Volker Roeber (Hazard and Risk Evaluation Research Division)