An Evaluation of Image Velocimetry Techniques under Low Flow Conditions and High Seeding Densities Using Unmanned Aerial Systems

Image velocimetry has proven to be a promising technique for monitoring river flows using remotely operated platforms such as Unmanned Aerial Systems (UAS). However, the application of various image velocimetry algorithms has not been extensively assessed. Therefore, a sensitivity analysis has been conducted on five different image velocimetry algorithms including Large Scale Particle Image Velocimetry (LSPIV), Large-Scale Particle Tracking Velocimetry (LSPTV), Kanade−Lucas Tomasi Image Velocimetry (KLT-IV or KLT), Optical Tracking Velocimetry (OTV) and Surface Structure Image Velocimetry (SSIV), during low river flow conditions (average surface velocities of 0.12−0.14 m s - 1 , Q60) on the River Kolubara, Central Serbia. A DJI Phantom 4 Pro UAS was used to collect two 30-second videos of the surface flow. Artificial seeding material was distributed homogeneously across the rivers surface, to enhance the conditions for image velocimetry techniques. The sensitivity analysis was performed on comparable parameters between the different algorithms, including the particle identification area parameters (such as Interrogation Area (LSPIV, LSPTV and SSIV), Block Size (KLT-IV) and Trajectory Length (OTV)) and the feature extraction rate. Results highlighted that KLT and SSIV were sensitive to changing the feature extraction rate; however, changing the particle identification area did not affect the surface velocity results significantly. OTV and LSPTV, on the other hand, highlighted that changing the particle identification area presented higher variability in the results, while changing the feature extraction rate did not affect the surface velocity outputs. LSPIV proved to be sensitive to changing both the feature extraction rate and the particle identification area. This analysis has led to the conclusions that for surface velocities of approximately 0.12 m s - 1 image velocimetry techniques can provide results comparable to traditional techniques such as ADCPs. However, LSPIV, LSPTV and OTV require additional effort for calibration and selecting the appropriate parameters when compared to KLT-IV and SSIV. Despite the varying levels of sensitivity of each algorithm to changing parameters, all configuration image velocimetry algorithms provided results that were within 0.05 m s - 1 of the ADCP measurements, on average

The evaluation of rating curve in bed rivers with sediment transport

The measure of the water discharge in rivers is important within the cognitive actions addressed to identify a management policy concerning the water resources. In particular, it is essential for a planning of the interventions in a middle and long term in relation to the control activity and environmental protection respectly to the forecasting and prevention of natural hazard. The measure methods in natural channels are generally based on the use of hydrometers combined with rating curves in steady flows. The relation between water level and discharge is determined by measures of velocities in conditions of low and mean flows, and more rarely during high flows. In the latter case, practical difficulties in measurement lead to extrapolate discharge values on statistical basis which could involve significant errors in rating curves at high levels. Furthermore the steady rating curve cannot to estimate in rigorous way the discharges in presence of sediment transport, which often happens with the high flows modifying the geometrical and morphological river characteristics. In this context, the present work describes a numerical-experimental approach to estimate the water discharges on the basis of numerical models at fixed and mobile bed, calibrated by simultaneous measure series of water level and velocities in gauged stations. In the first step, the application of fixed bed model allowed a more accurate extrapolation of rating curves for elevated discharges through the roughness coefficient correction. Successively the use of the mobile bed model, considering simplified hypothesis, allowed to analyze the sediment transport effects on rating curve shape. The reliability of such approach has been evaluated on a gauged section located upstream a single thread alluvial reach in the middle valley of the Noce River in Basilicata region (Italy). This reach is characterized by a narrow and confined bed, which was interested by a progressive morpho-hydrodynamic change caused by a landslide in the right side slope of the basin in July 2007

La gestione delle risorse idriche nella città dei Sassi (Matera)

Negli ultimi anni i Sassi di Matera sono passati da vergogna a orgoglio nazionale. L’insieme delle chiese rupestri, degli scavi nelle rocce, dei numerosi ipogei, cisterne e palombari sono un sistema architettonico, ingegneristico e paesaggistico unico al mondo riconosciuto dall’UNESCO. La gestione delle risorse idriche è un elemento che ha condizionato fortemente lo sviluppo e l’assetto complessivo dei Sassi di Matera. In particolare, la città antica presenta una serie di opere e di sistemi diffusi di accumulo che consentirono uno sviluppo urbano significativo in cui le acque piovane venivano parsimoniosamente raccolte e accumulate in sistemi di cisterne spesso connesse tra loro. Nella presente memoria si riportano le evidenze di tale sistema e alcuni esempi emblematici relativi al complesso sistema di gestione delle risorse idriche

Data on the harmonization of image velocimetry techniques, from six different countries

Here, we present a range of datasets that have been compiled from across six countries in order to facilitate image velocimetry inter-comparison studies. These data have been independently produced for the primarily purposes of: (i) enhancing our understanding of open-channel flows in diverse flow regimes; and (ii) testing specific image velocimetry techniques. These datasets have been acquired across a range of hydro-geomorphic settings, using a diverse range of cameras, encoding software, controller units, and with river velocity measurements generated as a result of differing image pre-processing and image processing software

Data on the harmonization of image velocimetry techniques, from seven different countries

Here, we present a range of datasets that have been compiled from across seven countries in order to facilitate image velocimetry inter-comparison studies. These data have been independently produced for the primarily purposes of: (i) enhancing our understanding of open-channel flows in diverse flow regimes; and (ii) testing specific image velocimetry techniques. These datasets have been acquired across a range of hydro-geomorphic settings, using a diverse range of cameras, encoding software, controller units, and with river velocity measurements generated as a result of differing image pre-processing and image processing software