Abstract
The past few years have seen the raise of unmanned aerial vehicles (UAV) in geosciences for generating highly accurate digital elevation models (DEM) at low costs, which promises to be an interesting alternative to satellite data for small river basins. The reliability of UAV-derived topography as input to hydraulic modelling is still under investigation: here, we analyse potentialities and highlight challenges of employing UAV-derived topography in hydraulic modelling in a tropical environment, where weather conditions and remoteness of the study area might affect the quality of the retrieved data. We focused on a stretch of the Limpopo River in Mozambique, where detailed ground survey and airborne data were available. First, we tested and compared topographic data derived by UAV (25 cm), RTK-GPS (50 cm DEM), LiDAR (1 m DEM) and SRTM (30 m DEM); then, we used each DEM as input data to a hydraulic model and compared the performance of each DEM-based model against the LiDAR based model, currently used as benchmark by practitioners in the area. Despite the challenges experienced during the field campaign—and described here—, the degree of accuracy in terrain modelling produced errors in water depth calculations within the tolerances adopted in this typology of studies and comparable in magnitude to the ones obtained from high-precision topography models. This suggests that UAV is a promising source of geometric data even in natural environments with extreme weather conditions.
Highlights
Accounting for more than 40% of all natural hazards worldwide and half of all deaths caused by natural catastrophes (Ohl and Tapsell 2000), floods have a strong socio-economic relevance
A consistent result in our analyses is that shuttle radar topography mission (SRTM) always overestimates both terrain elevation estimated with light detection and ranging (LiDAR), unmanned aerial vehicles (UAV) and real-time kinematic (RTK)-GPS and the river bathymetry due to issue on measuring underwater geometry during normal or high flow conditions
The SRTM data were recorded during a 11-day mission on February 2000, corresponding to a disastrous flood occurred on the Limpopo river, leading to the uncertain assessment of the topography below the extended flooded surfaces by SRTM
Summary
Accounting for more than 40% of all natural hazards worldwide and half of all deaths caused by natural catastrophes (Ohl and Tapsell 2000), floods have a strong socio-economic relevance. It has been estimated (Jonkman and Vrijling 2008) that in last decade of the twentieth century, floods were responsible for the loss of about 100,000 human lives and affected more than 1.4 billion people worldwide. DEMs can be obtained from different surveying tools and data techniques, ranging from traditional ground surveying to remote sensing techniques applied to air- or spaceborne imagery. The most common space-borne topography data are the shuttle radar topography mission (SRTM) DEM (Hensley et al 2001) and the advanced spaceborne thermal emission and reflection radiometer (ASTER) DEM (Nikolakopoulos et al 2006; Zandbergen 2008; Wang et al 2012)
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