Beach Response to Wave Forcing from Event to Inter-Annual Time Scales at Grand Popo, Benin (Gulf of Guinea)

Abstract

This paper assesses the morphological storm-event impact, seasonal cycles, trends of wave forcing, and beach's response at the coastal area of Grand Popo, Benin. Three and a half years' worth of data were collected from 2013 to 2016, using a video system calibrated with field data collected during a 10 day experiment. A comparison was carried out with Wavewatch III IOWAGA wave hindcast data. The along-shore-averaged shoreline position exhibited a seasonal pattern, which was related more to the average wave height than the average storm intensity. Storms occur in austral winter (June, July, August, and September). Based on 12 storms, the results revealed that the average storm duration was 1.6 days, with a mean erosion of 3.1 m. The average post-storm beach recovery duration was 15 days, and the average recovery rate was 0.4 m/day. The impact of storms was more or less amplified depending on the eroding and accreting periods of the wave climate. There was an inter-annual eroding trend of about −1.6 m/year, but the causes of this trend could not be explained.

Why and How Do We Study Sediment Transport? Focus on Coastal Zones and Ongoing Methods

“…Scientific issues are common, and digital communication has allowed researchers to multiply worldwide collaborations, disrupting the production of knowledge. This special issue thus reflects the ongoing international cooperation between northern and southern countries on sensitive topics of common interest, thanks to the support of scientific research organizations such as the Institute of Research for Development in France, or through dedicated projects [57,351,[353][354][355][356].…”

“…This special issue also contains works whose purpose is to quantify volumes of sediments transiting between morphological domains (estuary, beaches, spit, shelf) or which are redistributed between adjacent compartments, and which shape the coast at seasonal and interannual scales. Several illustrations concern sandy coasts in Senegal [57], Benin [351], Australia [352] and Vietnam [353], and one illustration concerns a muddy environment along the Mekong Delta [354]. Volumes of transported sediments serve as a basis for studying processes and for sensitivity analysis of shoreline changes under different forcing.…”

“…The morphological storm-event impact, seasonal cycles, trends of wave forcing, and beach's response along the Grand Popo beach in Benin by Abessolo Ondoa et al [351] is based on three years and half of video data calibrated during a 10-day experiment, and on wave hindcast data. The alongshore shoreline position is affected seasonally, modulated by the wave height, and by winter storms, with 12 storms of averaged duration 1.6 days, mean erosion 3.1 m, and mean recovery duration of 15 days.…”

Beach adaptation to intraseasonal sea level changes

“…This study focuses on beach changes at Grand Popo (Benin) near the border with Togo, in the Bight of Benin, Gulf of Guinea (figure 1). According to the classification of Wright and Short (1984), Grand Popo beach is an intermediate to reflective beach, characterised by a steep upper slope, an alongshore-uniform flat low-tide terrace (Almar et al 2014, Abessolo et al 2016, 2017b. Bathymetric iso-contours are reasonably uniform alongshore (Almar et al 2014).…”

“…The first pilot research video station in West Africa was installed in February 2013 on a 20-m high tower located approximately 70 m from the shoreline (Almar et al 2014, Abessolo et al 2016Abessolo et al , 2017aAbessolo et al , 2017b). An on-site computer processes the raw image-frames and stores 15-min time stack (Holland and Holman 1993) and timex (Holland et al 1997) images.…”