Prefeasibility study for the Port of Itajai

Abstract

In southern Brazil, in the province of Santa Catarina, the port of Itajai is situated. The port is located at the mouth of the river Itajai-Acu, about 3 km inland. The Port of Itajai is very important for both the local and national economy because of its role in foreign trade, and due to this prominent role in the community many stakeholders are involved. To allow larger vessels into the harbour of Itajai there has been a constant process of deepening the approach channel and the harbour basin. In order to compete sedimentation process in the harbour basin will change. From a commercial point of view it is very interesting to search for other solutions to keep the river at the required depth besides dredging. There are four main principal solutions to reduce the sedimentation of the harbour basin: reduce the sediment production, reduce the transport capacity of the river, increase the flow velocity and redirect the sediment. All these possibilities have a positive effect on the sedimentation in the harbour. Reducing the transport capacity of the river with the use of a sand trap is expected to have the most effect. with surrounding harbours it is important to allow safe navigation of larger vessels as this results in greater cargo handling at lower cost. Due to recent developments the Port of Itajai is investigating the possibility to receive vessels with a length of 300 m overall, 45 m beam and 14 m draught. The Port of Itajai is facing two different kinds of problems, one concerning the alignment and the other concerning sedimentation. In order to deal with the problems the current situation was mapped. The river, sea and harbour characteristics are given; river discharges, flood events, harbour development, harbour lay out, tide, wind and wave direction. At this moment the approach channel of the harbour deals with some imperfections, which makes it difficult, sometimes even impossible, for the design vessel to sail through the channel. Also the current turning circle is a problem as turning of the new design vessel will be extremely difficult and the safety is questionable. With a cost benefit analysis the best possible location for a larger turning basin is determined and a number of changes for the alignment are given. Without human interventions the estuarine system would be in a dynamic equilibrium. The bathymetry would adjust to varying conditions and oscillate around this dynamic equilibrium depth. This is the depth for which the average annual sedimentation is zero. When the natural dynamic equilibrium is disturbed as a result of deepening the estuary, the system will try to restore itself. This causes sedimentation and maintenance dredging is required to maintain the newly dredged areas. The volume of the required maintenance dredging depends on the extent of the disturbance in relation to the equilibrium situation. A larger deepening will lead to smaller flow velocities and therefore to higher sedimentation rates. The sedimentation that occurs in the Itajai Acu estuary is a complex ensemble of processes, which is influenced by processes at the boundary conditions. The two most important processes are the tidal fluctuations and river discharge. To gain insight in the wet system, hand calculations and a 1D-computer model were made. The effect of a number of human interventions on the Itajai-Acu river are determined with hand calculations. With the 1D-modelling software, SOBEK, the effects of the planned dredging are determined.