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

This contribution presents measurements that qualitatively and quantitative ly 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 s ystem that was deployed on a 30 m tower located at the Barra Nova Inlet, Al garve, Portugal. The results presented here quantify several key features o f this mesotidal, mixed-energy inlet system and their response to forcing b y incident waves and tidal sea level change. Storm events were highly corre lated with rapid erosion of the barrier island on the western, down-drift s ide 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 wa s of the order of 0.47 m/day, which equates to an overall erosion of approx imately 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 w ere not found to be directly related to incident wave conditions. The posit ion of the inlet channel migrated 75 m (0.35 m/day) in a southeast directio n, toward Ilha da Barreta, which is consistent with the prevailing directio n of longshore sediment transport. The orientation of the inlet channel als o underwent significant shifts of up to 22 degrees /month between across-sh ore 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 se diments. These sediments are then steadily reworked by a combination of tid al flows and smaller waves prevailing from the southwest. (C) 2001 Elsevier Science B.V, All rights reserved.