Interaction between Coastal Development and Inland Estuarine Waterways at the Short–Medium Timescale

Abstract

This article highlights the impact of tidal inlet modification on the evolution of inland estuarine waterways at the short–medium timescale. The study area is the Nerang River estuarine system located on the east coast of Australia. This estuary has been affected by a range of developments, including stabilization of its tidal entrance. This study is mainly focused on quantifying the tidal regime change and potential morphological and ecological implications resulting from these changes. To this end, the study started with field data collection and numerical modelling of the study area. The results of harmonic analysis showed that the Nerang Estuary responds nonlinearly to tidal forcing and is dominated by frictional forces. Analysis of water level and current time histories showed a mixed, predominantly semidiurnal, and flood-dominant tidal regime within the estuary. It also showed strong asymmetry of tide along the estuary. At the second stage of the study, historical data of the study area were analyzed and compared with the recently collected data. The purpose of this stage of the study was to understand the evolution of the estuary as a result of the changes at its entrance over the past 20 years. Variations in the ratio of amplitudes from M4 to M2 demonstrate that the Nerang Estuary nonlinear response to tidal forcing has reduced over the past 20 years. Analysis of historical data also suggests that the estuary has become less flood-dominant over the past 20 years, and as a result, the balance between tide-influenced sediment infilling and sediment flushing of the estuary during freshwater flooding events may have shifted toward transporting more sand out of the estuary.