ABSTRACT
Nowadays, sediment management has an economic and environmental challenge to maintain the activity and movement of trade ships. This study was carried out on the case of Zarzis commercial harbor (Tunisia) presenting an important silting, which limits its draft and consequently its economic situation. The studied area presents a significant volume of dredged sediments. The objective of this work is to identify the main source of silting problem in Zarzis harbor. Indeed, the increase of sediment layer prohibits ships movement that arrests the commercial activity of Zarzis harbor.
This paper investigates the influence of hydrodynamic factors, such as waves and currents, on sediment mobility in Zarzis harbor, Tunisia. Furthermore, the major silting observed in the studied area was deduced by bathymetry campaigns carried out over the years. A geographic information system software (ArcGIS 9.3) was used to establish the harbor bathymetric maps for the years 2006, 2008, 2010 and 2015. Results show an accumulation of 6 meter thick layer of sediment in the shipping channel. In order to understand the nature of sediment behavior under combined current– wave action at Zarzis harbor, three bed shear stresses were studied: Stress due to waves only (τ w), Stress due to current only (τ c) and stress due the combined role of current and waves (τ cw). τ cw values were calculated using Soulsby (1995).
The contribution of waves, currents and their combined effect on the generated seabed shear stress was analyzed based on Acoustic Doppler Current Profiler (ADCP) results as well as particle size distribution analysis performed on marine sediments sampled from 44 sites throughout the studied harbor. The determined seabed shear stress in different zones of the harbor was then compared to the critical threshold value defined by the Shield parameter. Overall, results showed the dominant action of waves in sediment mobility, especially in the shipping channel. The stress due to waves only (τ w) exceeded the threshold value for almost all the studied samples. However, the action of current only did not contribute in the silting problem at the studied harbor.
