Measurements of the response of a coastal inlet using video monitoring techniques

This contribution presents measurements that qualitatively and quantitatively describe the response of a coastal inlet system to forcing by waves and tides over a seven-month period using advanced video monitoring techniques. Measurements were obtained from an autonomous solar-powered video camera system that was deployed on a 30 m tower located at the Barra Nova Inlet, Algarve, Portugal. The results presented here quantify several key features of this mesotidal, mixed-energy inlet system and their response to forcing by incident waves and tidal sea level change. Storm events were highly correlated with rapid erosion of the barrier island on the western, down-drift side of the inlet (Ilha da Barreta). The vegetated dunes of Ilha da Barreta eroded 60 m in a single storm event, equating to an erosion rate in excess of 3 m/day. The average erosion of Ilha da Barreta over the study period was of the order of 0.47 m/day, which equates to an overall erosion of approximately 100 m, approximately 80% of which was caused by storm events. As a consequence of this erosion the inlet width increased by approximately 60 m over the seven months. The position and orientation of the inlet channel were not found to be directly related to incident wave conditions. The position of the inlet channel migrated 75 m (0.35 m/day) in a southeast direction, toward Ilha da Barreta, which is consistent with the prevailing direction of longshore sediment transport. The orientation of the inlet channel also underwent significant shifts of up to 22 degrees /month between across-shore and down-drift skewed (north-south) alignment during the study period. Overall these results suggest that the long-term morphological evolution of the Barra Nova Inlet system is strongly influenced by extreme storm events that erode and liberate large quantities of previously stable vegetated sediments. These sediments are then steadily reworked by a combination of tidal flows and smaller waves prevailing from the southwest. (C) 2001 Elsevier Science B.V, All rights reserved.