Coastal Flooding Caused by Extreme Coastal Water Level at the World Heritage Historic Keta City (Ghana, West Africa)

Abstract

Like low-lying sandy coasts around the world, the Ghanaian coast is experiencing increasingly frequent coastal flooding due to climate change, putting important socioeconomic infrastructure and people at risk. Our study assesses the major factors contributing to extreme coastal water levels (ECWLs) from 1994 to 2015. ECWLs are categorized into low, moderate, and severe levels corresponding to the 30th, 60th, and 98th percentiles, respectively. Using these three levels over the Pleiades satellite-derived digital elevation model topography, potential flood extent zones are mapped. ECWLs have the potential to flood more than 40% of the study area, including socioeconomically important sites such as tourist beach resorts, Cape St. Paul lighthouse, and Fort Prinzenstein. In this study, all coastal flooding events recorded by the municipality of Keta fall within the 98th percentile category. Our results show a gradual increase in the frequency of flooding over the years. Flooding events are caused by a compound effect of the tide, sea level anomaly, waves, and atmospheric conditions. Finally, while wave run-up is the major contributor to coastal flooding, the tide is the one varying most, which facilitates a simple early warning system based on waves and tide but adds uncertainty and complicates long-term predictability.

Remote Data for Mapping and Monitoring Coastal Phenomena and Parameters: A Systematic Review

“…Regarding dissolved iron products, Zanaty et al [61], for example, compared land use and land cover maps with some water quality products that were provided by CMEMS to assess the anthropogenic impacts on environmental sustainability. Regarding hydrodynamic products, Brempong et al [62], for example, utilized data produced by the Laboratory of Geophysical and Oceanographic Spatial Studies of Toulouse to assess the major factors contributing to coastal flooding. Regarding sea level altimetry products, Passaro et al [63] and Pujol et al [64], for example, compared some products.…”

“…The eligible papers that mapped and/or monitored DSM. DSM (1) Avulsion sites TanDEM-X (12 m) No -[340] -DSM (1) Coastal aquaculture ponds -Yes [212] -[210] DSM (1) Coastal forested wetland UAV No -[341] -DSM (1) Coastline change -Yes [150,269,342,343] [ [344][345][346] [347] DSM (1) Coastline change UAV No [348] -DSM (1) Coastal [350] DSM (1) Coastal vulnerability assessment -Yes [116] -[166,351] DSM (1) Coastal vulnerability assessment ASTER Yes --[102] DSM (1) Coastal vulnerability assessment Pleiades (0.5-2 m) No --[352] DSM (1) Coastal vulnerability assessment SRTM DEM, USGS (30 m) Yes -[275] -DSM (1) Coastal vulnerability assessment VENµS No --[274] DSM (1) Coastal wetland classification Airborne lidar No -[353] -DSM (1) Flood extent -Yes --[109] DSM (1) Flood extent Pleiades stereo image (0.5-2 m) No [62] [354] -DSM Flood risk -Yes --[60] DSM (1) Habitat -Yes --[355] DSM (1) Habitat Airborne lidar No -[277] -DSM (1) Habitat NASADEM Yes [215] --DSM (1) Habitat Sentinel-1 (~10 m) No [165] --DSM (1) Habitat UAV No - [277,[356][357][358] [279,359,360] DSM (1) Habitat UAV-LiDAR No - [142,361] DSM (1) Intertidal polychaete reefs DJI Phantom 4 Multispectral UAV No - [8...…”

“…] -Flood (1) Flood extent Sentinel-1 (~10 m) No [107] [120] -Flood (1) Flood extent Sentinel-2 (10-20-60 m) No [107] --Flood (1) Flood extent Pleiades stereo image (0.5-2 m) No [62] --Flood (1) LU/LC change ASAR Yes -[108] -Flood (1) LU/LC change MODIS (0.5-1 km) No -[108] -Flood (1) LU/LC change TerraSAR-X Yes -[108] -Flood (1) Sea level rise -Yes [384] -- (1) This parameter was mapped and monitored together with other parameters.…”

“…SLA (1) Fishing zones -Yes [303] --SLA (1) Flood extent -Yes [62] [354] -SLA (1) Global tide -Yes --[502] SLA (1) Global tide FES2014 Yes --[503] SLA (1) LU/LC change -Yes --[443] SLA (1) Influence of El-Nino -Yes --[472] SLA (1) Plastic litter -Yes --[146] SLA (1) Sea level anomaly -Yes [64] - [63,144,[504][505][506][507]] SLA (1) Sea level anomaly Jason- SLA (1) Sea level anomaly X-TRACK multisatellite Yes --[144] SLA (1) SST Yes --[510] SLA (1) Subsidence Sentinel-1 (~10 m) No -[379] -SLA (1) Tidal evolution X-TRACK multisatellite Yes -[511] -SLA (1) Tidal flat -Yes -[375] -SLR (1) Sea level rise -Yes [384,456] [381]…”

Sea Level Rise-Induced Transition from Rare Fluvial Extremes to Chronic and Compound Floods

“…Local scale modeling and process studies of SLR impacts on compounding of extreme flood events and HTF have been understudied. Moreover, these studies have typically focused only on extreme flooding induced by tropical cyclones (TCs)/extreme coastal water level [4,21,[36][37][38][39]. Numerical modeling of HTF, on the other hand, is still under-explored in flood research.…”