Topographic Survey: River Ouse, York

Mott McDonald Bentley, Wessex Archaeology and the Environment Agency

In recent months, we’ve made a number of visits to York, where we’ve been conducting an extensive aerial survey of land adjacent to the River Ouse.

Following torrential rain and subsequent flooding in December 2015, the Environment Agency took the decision to review and improve flood defences involving the Foss Barrier. The barrier features a gate that can be closed to prevent rising waters in the Ouse from backing up into the River Foss and flooding parts of the city. However, in 2015, these measures had proven inadequate. Having devised an improvement plan, the Agency appointed Mott McDonald Bentley to deliver the necessary upgrades, which include fitting eight new, high capacity pumps and associated control systems.

As part of this work, the company commissioned a survey of properties set close to the banks of the river. The intention was to measure the heights of thresholds and, thus, to determine their susceptibility to flooding. The work would include both a land-based and aerial survey, with Suave appointed to deliver the latter.

The use of a UAV was especially appropriate for obtaining details of inaccessible or potentially dangerous areas such as riverbanks, where human operatives on the ground or water might have been at risk.

The drone-based survey enabled us to produce an accurate 3D model and data that was subsequently combined with a hand-held laser survey conducted by Wessex Archaeology. Together, these two techniques produced a detailed survey of thousands of local properties. This will be a valuable asset to the Environment Agency and its contractors when carrying out future flood modelling work.

The aerial survey delivered an overall accuracy of better than 3cm RMSE, which was the figure specified by the client.T he survey information was subsequently used to produce detailed topographic drawings with contours and additional data points. Ultimately, it is hoped that these will be used as part of an interactive model.

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