Motion of a Debris Line Source under Currents and Waves: Experimental Study

Debris impact has an important role in structural damage during extreme coastal events. Understanding the transport of debris and the characteristic of its motion is crucial because the debris impact depends on debris motion. This study investigated floating debris dispersion and motion by conducting laboratory experiments that considered the effects of a structural array, or a gridded layout of city-like buildings. Physical model experiments were conducted for two different hydrodynamic conditions: (1) current only; and (2) current + wave combined cases. Debris was released from a certain height in a repeatable way. Visual data were collected by four overhead video cameras and a particle tracking algorithm was implemented to track debris motion. Onshore debris spreading was much larger in the current + wave combined cases than in the current only trials. The results indicated that the structural array restricted the lateral spreading of debris onshore, and between the buildings, the spread of the particles approached a Gaussian distribution as the particles move inland. The offshore dispersion of debris particles was slightly higher when structures were present due to the additional turbulence that was created by the reflected waves. Debris spreading angles (theta s) were calculated for each case and compared with the angles used in the current engineering practice. The presented results aimed to increase the current knowledge on debris motion and spreading during extreme events, such that engineers might build more resilient coastal communities.