Drones over the delta: Monitoring coastal protection structures along the shoreline of Ghana’s Volta delta using an Unmanned Aerial Vehicle (UAV)

Coastal erosion in the Keta district of the Ghana’s Volta delta is causing increasing problems by destroying property and infrastructure and displacing people. With erosion rates of up to 8 metres per year, proactive efforts are required to manage these impacts. Within the Keta Sea Defence Project (KSDP) various erosion control measures have been employed. These include hard engineering, such as groynes and revetments, and soft engineering, such as beach nourishment.

Since its establishment in 2004, there has been no sustainable scheme in place to monitor the effectiveness of the coastal defence structures within the Keta Sea Defence Project.
Traditional methods of monitoring the rate of coastal erosion include Differential Global Positioning Systems (DGPS), aerial photographs and satellite imagery – but these are expensive to buy, require specialist training to use, and can be time consuming. Although some satellite images are freely available, their coarse resolution (30m x 30m) mean that that are unsuitable for monitoring the KSDP.

Kwasi Appeaning Addo and his team in the Department of Marine and Fisheries Sciences at the University of Ghana and the Centre for Tropical Marine Ecology at the University of Bremen, Germany are pioneering a new mechanism to monitor the rate of coastal erosion. Unnamed Aerial Vehicles (UAVs) or “drones” are relatively inexpensive to buy (less than US$1000) and easy to use (it takes only a day to train research assistants to fly the drone). In addition they allow flexibility in the monitoring process – the researchers determine the flight path and the altitude at which the drones fly, which results in much more relevant and reliable data. Being able to choose the height at which the drones fly means that clouds are not a problem as they can be in both aerial photographs and satellite imagery.

Dr Appeaning Addo and his team have been undertaking bi-monthly repeated surveys were undertaken using a drone known as DJI Phantom Series. They first established ground control points using a high precision differential GPS system in order to effectively guide the drone. The survey produce in high resolution aerial photographs which are then analysed and used to create 3D models of the earth’s surface. The models from each drone monitoring mission are then overlaid with the previous ones. In comparing them, it is possible to identify any changes over time and also the extent of change allows calculation of the rate at which the change was occurring. Since the drones produce photographs, it is possible to use them to investigate of what is causing the changes and whether they are permanent or cyclical, for example. The preliminary results from two months (May and July 2015) of drone-led field surveys showed that there was significant lateral and topographic changes in the beach system.

As drones provide more reliable data for scientists to analyse, they will be able to have a greater understanding of the nature and rate of coastal erosion in the Volta Delta shoreline. This provides a reference point to assess the effectiveness of the KSDP. It also provides important information for the government of Ghana to ensure that their attempts to address coastal erosion are well targeted and effective

View Kwasi Appeaning Addo's interview here

View drone footage of coastal flooding here

Posted 19/05/2016 12:12 by K. Appeaning Addo; Philip-Neri Jayson-Quashigah; Alession Rovere; Thomas Mann and Elisa Caella

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