Dams and climate change accelerate channel avulsion and coastal erosion and threaten Ramsar-listed wetlands in the largest Great Barrier Reef watershed

Abstract

• Dam-induced sand settling in the Burdekin River delta is raising the flood levels and threatening channel avulsion. • This trapping of sand in the Delta is starving the coast of sand and generating rapid coastal erosion. • Climate change is enhancing this coastal erosion as in the last few decades the mean sea level and the frequency of strong winds have increased significantly. • This is threatening Ramsar-listed wetlands of international significance. • The connectivity of water and sediment between the various parts of river basin demonstrates the need to manage the river at the basin scale using ecohydrology principles. This study documents the impact of climate change and human activities on the Burdekin River delta and coast. The Burdekin River is located in the dry tropics with a seasonally and interannually highly variable discharge, controlled by occasional cyclones and the ENSO-dependent monsoon. Even though the peak discharge from cyclonic rainfall is decreased by a dam, large floods still occur during long-duration monsoon. While the dam traps much of the coarse sediment runoff, large amounts still reach the Delta originating from catchments downstream of the dam. The riverbed in the Delta has measurably risen in recent decades. In turn, this increases the flood levels and the threat of channel avulsion. Sand trapping by the dam and in the Delta is also starving the coast of sand, and this generates rapid coastal erosion along the 11 km long Cape Bowling Green peninsula. Climate change is enhancing this coastal erosion as in the last few decades the mean sea level and the frequency of strong winds have increased significantly. The peninsula may breach soon. As the peninsula protects Ramsar-listed wetlands of international significance, its breaching is predicted to impact the fisheries that depend on the Cape (the black marlin billfish) and on the wetlands (mud crabs, barramundi and mangrove jacks), as well as shorebirds and waterbirds. These findings demonstrate the connectivity of water and sediment throughout the river basin and the coast, and the need for management at the basin scale using ecohydrology principles.