Morpho-Dynamics Shoreline Offset at the Entrance of Qua Iboe River Estuary, South East Coast of Nigeria

Saviour P Udo-Akuaibit

The morpho-dynamic variability of shorelines was examined to ascertain the causes of shoreline offset around the entrance of Qua-Iboe River estuary, south-east coast of Nigeria. Shoreline mapping revealed a landward updrift shoreline offset displacement relative to the estuary mouth over a distance of 600 m off the former seaward limit. Daily beach profiles showed an averaged beach width of 200 m with a concave foreshore contiguous to the estuary mouth at the updrift side while the downdrift was characterised by a narrow beach width of 190 m and a convex foreshore. The updrift surf-zone was three times higher in surf-scaling parameters which caused higher rates of erosion and volumetric loss of sediment compared to the downdrift side which was characterised by accretion. The shoreline offset was attributed to the actions and forces of wind/wave, tidal and long-shore currents on the shoreline which were accentuated by storm surge incidence in 2011. A clockwise rotation of the ebb tidal channel in the delta at the estuary mouth estimated at a period of 9 years and a shift in the ebb tidal delta in the downdrift direction offered the best explanation to the updrift erosion phenomenon. Moreover, Estuary-Deltaic-Surf zone processes were noted as a system which modulates the morpho-dynamic variability of the shoreline. A programmed monitoring by appropriate government agencies of the changes and maintenance of the ebb tidal delta through periodic beach replenishment with sediment are recommended as sustainable shoreline protection strategies.