Millennial and contemporary dynamics of the barrier estuary entrance at Moruya, SE Australia

This study presents optically stimulated luminescence (OSL) dates, sediment coring, historical maps and charts and photography and airborne LiDAR to reconstruct the millennial and contemporary history of the Moruya River entrance. OSL dating reveals small estuarine beaches were active between 7000 and 5000 years ago, when the entrance was far more open than at present. At that time, a large flood-tide delta infilling a wide immature estuary is likely to have existed. Continued progradation of the Bengello barrier to the north, and the inception of the Moruya Heads barrier to the south from 4500 years onward, progressively constricted the river entrance. Several more low-energy estuarine beaches developed behind the Moruya Heads barrier and are dated to ~4400 and ~2800 years ago. Concurrently, the open mud basin of the estuary infilled with fluvial sediment. Following the arrival of Europeans in the region, in the early to the mid-1800s, engineering works were undertaken in stages to train the estuary entrance for navigation and have further constrained the system. OSL dating of beaches formed as a result of this activity concur with the historical accounts. These contemporary changes to the entrance have modified the estuary hydrodynamics and shifted the sediment transport and ecological regime of the lower estuary.