Groynes are cross-shore structures designed to reduce longshore transport on open beaches or to deflect nearshore currents within an estuary. On an open beach they are normally built as a series to influence a long section of shoreline that has been nourished or is managed by recycling. In an estuary they may be single structures.
Estuaries form a transition zone between river environments and maritime environments. Under estuaries we also include fjords, lagoons, river mouths, and tidal creeks. River and estuary flooding can be a severe risk for the river floodplain. In coastal rivers and estuaries flooding can stem from up-stream causes (like heavy rainfall or melting snow) and also from maritime events (storm floods).