Incorporating estuaries as a source or sink of sediment within assessments of coastline risk and adaptation to climate change

Complex coastal landforms exhibit variable behaviour in response to sea-level rise. A proposed modelling framework that integrates shoreline changes associated with longterm recession, short-term variability and sea-level rise advocates that coastal risk assessment be undertaken within the context of a geomorphologically-based modelling framework whereby a coastline is subdivided into coastal compartments or cells, thereby recognising the sedimentary links between compartments. For example, the Narrabeen coastline includes bounding headland compartments, a bay compartment and an estuary compartment; and the behaviour of the coastline varies according to the response of each of these compartments to variable climatic and oceanic conditions. This approach is extended to other estuarine systems in southern NSW. Estuaries play an important role as a source or sink of sediment that varies widely in accordance with climatic and oceanic conditions. Accounting for the role of estuaries in coastline behaviour involves identifying the variable shorelines within estuaries; establishing the long-term estuarine shoreline behaviour and the response of shorelines to sea-level change; and integrating models that best represent the response of estuarine shorelines to climate change within the proposed integrated modelling framework for coastal risk assessment. Recognising the links between sedimentary sources and sinks and integrating models of estuarine behaviour with models of open coast behaviour will improve coastal risk assessment and provide greater confidence in adaptation options.