Water & Wastewater Treatment Magazine
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www.wwtonline.co.uk | WWT | JUNE 2015 | 19 Project focus T he use of aerial surveys from unmanned aerial vehicles (UAVs) has proved effective in mapping flood risk for the Environment Agency at the River Mole in Surrey. UAVs – commonly known as drones – are growing in popularity as a method of conducting surveys and inspections in hard-to-reach areas where high quality data and modelling is required. In response to the storms which Environmental Management Drone imagery helps map River Mole flood risk Project focus ● Surveys required in area hit by 2013/4 winter floods ● UAVs used to provide low-level high resolution imagery ● 360-degree videography and elevation modelling produced complete picture The River Mole rises in Horsham, West Sussex, and meets the Thames near Hampton Court Palace in South West London. At Island Barn Reservoir in South West London the river splits into two channels; the River Mole and the River Ember. The project involved conducting aerial surveys of the stretch of the river from the Esher-Hersham railway bridge in the south to where the rivers Mole and Ember reconnect above Island Barn Reservoir in the North. Flooding along the River Mole has the potential to cause significant damage on local, national and even international scales due to the amount of key infrastructure located in its catchment. This includes Gatwick Airport, East Surrey Hospital, two major motorways (the M25 and M23) and the London-Gatwick-Brighton railway line. The winter of 2013/14 was one of the wettest on record, with storms causing major flooding events throughout the entire country, including the River Mole catchment. Specific impacts of these floods included the closure of Gatwick Airport causing delays and cancellations of over 100 flights, widespread power failures and flooding of homes and commercial properties and extensive damage to transport infrastructure. UAVs were particularly suitable for the River Mole surveys for three main reasons. Firstly, the low levels which UAVs can fly at means they were ideal for capturing very high resolution aerial imagery and translating it into detailed photogrammetric elevation models. Secondly, UAVs can conduct surveys far more quickly than those being undertaken purely on the ground. This was a crucial factor in this project as the survey had to be undertaken whilst the level of the river was dropped, which could only be done for a limited amount of time Managing flood risk on the River Mole is crucial because of the amount of vital infrastructure in its catchment hit the River Mole – a tributary of the Thames - in winter 2013/14, Remote Aerial Surveys (RAS) were employed by Royal Haskoning DHV, on behalf of the Environment Agency, to conduct a range of low level aerial surveys of the area. The purpose of this was to locate and identify any issues in the channel, particularly those which could negate flood risk management, such as significant build-up of debris or damage to the river bank. The ability of the UAVs to fly low over the water was an important advantage