Thomas Edmund Fellowes , Ana Vila-Concejo , Shari L Gallop , Ryan Schosberg, Vincent De Staercke, John Largier 

Sandy beaches in estuaries and bays (BEBs) are common landforms on the coasts of many major cities. They exist under a wide range of settings and their morphology is controlled by their distance from the estuary/bay entrance, exposure to different types of waves (e.g., ocean swells vs locally generated wind waves), proximity to flood-tide delta/shoals, and anthropogenic interventions (e.g., dredging, groynes). Both swell waves propagating into estuaries/bays and locally generated wind waves can erode BEBs. However, more understanding of BEB storm erosion and recovery over decadal timescales is needed, as they typically respond slower than open coast beaches. Here we present decadal shoreline behaviours of nine BEBs from two estuarine systems in SE Australia, using 76 years of aerial imagery (1941–2017). We quantify and compare decadal behaviour between beaches, developing a new typology of BEBs based on shoreline evolution. We identify four decadal behaviours: prograding, quasi-stable, retreating and relict – and we assess the influence of flood-tide deltas, river mouths, distance from the entrance, and anthropogenic interventions. Swell-exposed BEBs near the entrance are quasi-stable and recover after storms at rates comparable to open coast beaches (<3 years). In contrast, BEBs further from the entrance and those with less swell exposure, have slower recovery timescales (3–15 years) and are controlled by storm return timescales. Prograding BEBs are typically far from the entrance, where fluvial, tidal and wind-wave processes dominate. Whether BEBs partially recover between storms (retreating) or never recover (relict) relates to storm frequency, recovery rates and proximity to sediment sinks (e.g., dredge sites, flood-tide deltas, tidal channels). Further, some BEBs are negatively impacted by anthropogenic interventions with slower recovery and/or prolonged erosion. Findings will help to better understand and manage BEB shorelines in major cities.