Sand load measurements in trailer suction hopper dredgers for beach and foreshore replenishments
Type:
Presented during:
WODCON XVII: "Dredging in a Sensitive Environment" - 2004, Hamburg, Germany
Authors:
Ing. B-J.F de Waard
Abstract: The dredging department from the North Sea Directorate of Rijkswaterstaat is responsible for maintaining the depth in the main access channel in the North Sea, which leads to the port of Rotterdam. The department also carries out beach- and foreshore replenishments to protect the Dutch shoreline. For this task trailer suction hopper dredgers (TSHD) from different contractors are used. To measure the loads of these hopper dredgers a sophisticated measurement system has been developed: MARS (Monitoring And Registration System). This system measures amounts of silt in tonnes dry solids for maintenance dredging in for example the fairway to Rotterdam and the amounts of sand in cubic metres for the beach and foreshore replenishments.
By using sensors that measure the draught of the vessel and the hopper level, it is possible to determine the volume of excavated material in the hopper. Rijkswaterstaat has been using the TDS system since 1988 for maintenance dredging to measure the amounts of dry solids for silt. Between 2001 and 2003 tests have been performed to see if it was possible to measure the amount of sand for the replenishments in cubic metres by using the same sensors as the TDS system.
When the amount of sand is measured, randomly manual soundings in the hopper are carried out to fine-tune the system. Tests on several TSHD have shown that these fine-tunings make the system very accurate and reliable.
Right now the system is being installed on all hopper dredgers that carry out beach and foreshore replenishments for Rijkswaterstaat and in the near future Rijkswaterstaat will use this system as the new payment system for the shore replenishments.
Keywords: measuring, replenishment, sand load, system, trailer suction hopper dredgers.