Measuring the volume of flushed sediments in a reservoir using multi-temporal images acquired with UAS

Abstract

We compute the volume of flushed sediments in a dam using photogrammetry-based multi-temporal surveys with an unmanned aerial system (UAS). Coping with sediments accumulation and erosion in reservoir is a living topic in modern hydraulics of dams, since the increase of sediment may reduce the reservoir capacity, endanger dam's stability, and represent an economical loss. As a result, a number of remedies can be considered, such as flushing or mechanical removal. To evaluate the performance of these operations, measuring the volume of removed sediments and their spatial distribution is important. Here, we show that photogrammetry from UASs represents a suitable solution to reckon the volume of removed sediments. The case study is the Fusino dam (Lombardia region, Northern Italy). Two surveys were performed, before and after sediment removal. In both cases, the flight has been planned with an average flight height equal to 65 m, leading to a mean ground sample distance (GSD) equal to 0.013 m. The 22 ground control points (GCP) used to adjust the photogrammetric block were measured with both global navigation satellite system (GNSS) and a total station. Each survey produced a cloud of about 40 million of points. Moreover, the digital surface model (DSM) produced by each photogrammetric flight has been validated with sample points measured with a robotic total station. Results show high consistency between computed DSMs and validation dataset, with a mean height difference equal, respectively, to 0.003 and ¡0.004 m considering the two different surveys, with a standard deviation around 0.05 m in both the cases. The volume of sediments flushed was estimated to be about 26,000 m 3 , which represents about 2%À3% of the total reservoir capacity. We estimated also a 6% difference in terms of reservoir capacity between the present condition and the no-sediments condition.

Centimetric Accuracy in Snow Depth Using Unmanned Aerial System Photogrammetry and a MultiStation

“…Images were acquired using a Canon EOS M camera with a fixed focal length of 22 mm, equivalent to a focal length of 35 mm in full-frame format. Both flights were planned following the guidelines by [36]. The average flight height for the summer and winter acquisitions was about 60 m, which corresponds to an average Ground Sample Distance (GSD) of about 0.02 m. The summer images were acquired at about 10 AM (local time), while the winter surveys were performed around midday (local time, Table 1).…”

“…These systems are commonly used for high-resolution surveys [29][30][31][32][33][34][35][36][37][38] as they allow flights to be performed in an automatic way [39,40]. The miniaturization of imaging and positioning sensors also reduces the payload and thus enables flights up to about one hour long [41].…”

Measuring the snowpack depth with Unmanned Aerial System photogrammetry: comparison with manual probing and a 3D laser scanning over a sample plot

“…Images were acquired using a Canon EOS M camera with a fixed focal length of 22 mm, equivalent to a focal length of 35 mm in 10 full-frame format. Both flights were planned following the guidelines by Pagliari et al (2016). The average flight height for the summer acquisition was about 65 m, whereas it was about 60 m for the winter survey, which corresponds to an average 4 The Cryosphere Discuss., doi:10.5194/tc-2017Discuss., doi:10.5194/tc- -57, 2017 Manuscript under review for journal The Cryosphere Discussion started: 24 April 2017 c Author(s) 2017.…”

Quantifying the Effects of Near-Bed Concentration on the Sediment Flux after the Operation of the Three Gorges Dam, Yangtze River

“…The main advantage of a RTK-GNSS survey is that it is faster, cheaper and easier to use during the surveying phase than classical topographic surveying [50]. Pagliari et al [50] compared the differences between coordinates of the ground-controlled points estimated using RTK-GNSS, and those computed from the classical topographic measurements, during processing photogrammetric block.…”