Dredging is often claimed to be killing the GBR. This document (14 MByte )  Sedimentary Geoscience of GBR-Larcombe-Ridd-Final(151202)    gives details of the natural sediment movements on the GBR. One of the conclusions (see page one) is that dredging moves a very small amount of sediment compared with natural influences such a sresuspension by the south easterly trade winds and cyclones. See sections 8.4 and 8.5 (pages 112 to 115)