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

Resumen

Bedform fields from the Piedras River mouth (Huelva, SW Spain) have been studied using side-scan sonartechniques, combined with visual scuba-dives, and direct geometric measuring. The dominant flow regime hasbeen 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 reversedduring tidal floods. During neap tides, larger bedforms maintain their geometry and position, whereas smallripples are re-oriented under different tidal conditions. Sand patches, dunes and ripples are interpreted as sedimentbypassing zones. Large forms indicate high energy flow, which can only migrate when flow velocity reachesthreshold values for the movement, with net sand transport towards open areas. Depositional features indicatelow, moderate, and high-energy conditions. Here, a depositional regime dominated by sediment accommodationis dominant, where sandy sediments are continuously remobilized, transported and re-deposited, even closer to theestuarine mouth. In inner zones finer particles, such as clay and silt, are transported by tides as suspended matterand deposited in protected inner areas. The final results are long narrow tidal flats, which alternate with sandyareas dominated by erosion.