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.