Bedform variability and flow regime in a barrier-inlet system. The mesotidal Piedras mouth (Huelva, SW Spain)

Abstract

Bedform fields from the Piedras River mouth (Huelva, SW Spain) have been studied using side-scan sonar techniques, combined with visual scuba-dives, and direct geometric measuring. The dominant flow regime has been determined from the results in these tidal environments, where erosive processes dominate during ebb, transporting sand as a bedload towards the mouth and central sector of the tidal channel. The process is reversed during tidal floods. During neap tides, larger bedforms maintain their geometry and position, whereas small ripples are re-oriented under different tidal conditions. Sand patches, dunes and ripples are interpreted as sediment bypassing zones. Large forms indicate high energy flow, which can only migrate when flow velocity reaches threshold values for the movement, with net sand transport towards open areas. Depositional features indicate low, moderate, and high-energy conditions. Here, a depositional regime dominated by sediment accommodation is dominant, where sandy sediments are continuously remobilized, transported and re-deposited, even closer to the estuarine mouth. In inner zones finer particles, such as clay and silt, are transported by tides as suspended matter and deposited in protected inner areas. The final results are long narrow tidal flats, which alternate with sandy areas dominated by erosion.