Papers by Slaven Conevski
XXXVI Convegno Nazionale di Idraulica e Costruzioni Idrauliche, IDRA 2018, 2018
6th Particles in Europe Conference, 2018, 2018
EGU General Assembly Conference Abstracts, Apr 1, 2019
The bedload distribution through the alluvial streams contributes in shaping of the river morphol... more The bedload distribution through the alluvial streams contributes in shaping of the river morphology. Therefore, bedload transport data are fundamental requirement for proper management of engineering practices in complex river systems. However, measurement series of bedload transport are seldom available and therefore statistically unreliable. The conventional methods can be notoriously hard and labor-intensive, entailing significant stochastic and systematic uncertainties mostly due to the spatio-temporal variability of the bedload as well as the instrument direct disturbance of the riverbed. Thus, the use of non-intrusive surrogate techniques could significantly reduce that uncertainty. Recently, many studies have demonstrated that the hydro-acoustics instruments are promising technique for bedload measurement. These sensors do not disturb the riverbed and are easy-to-deploy for long and frequent measurements. Some studies have reported strong correlations between the acoustic Doppler current profilers (ADCP) bedload measurements and the conventional bedload samplers. However, most of these methods are site-specific and require detailed calibration. This study investigates the capability of different ADCPs to measure the bedload velocity and bedload concentration. For those purposes, two laboratory and several field campaigns were conducted. The first series of laboratory experiments were performed in the hydraulic laboratories at UNIBO and UOttawa, focusing on evaluation of the apparent bedload velocity and the scattering processes occurring at the riverbed. The second campaign was conducted at NTNU laboratory aiming to validate the previous results and to further examine the acoustic parameters and signal processing configurations. At the same time the backscattering strength sensitivity towards the bedload concentration was fully examined. Two ADCPs were deployed at the same time on 0.7 m mutual distance (M9 Sontek, 1 MHz and 3 MHz and Stream Pro RDI, 2 MHz). Side and planar looking camera were deployed to measure the bedload velocity, active layer thickness and surface bedload concentration and a bedload trap was installed at the end of the flume to monitor the bedload transport rate. Different bedload transport conditions were reached by utilizing various sediment materials, (e.g., sand and gravel) and by adjusting the hydraulic conditions. De-spiking and filtering were applied to the raw data, and the temporal average of the apparent bedload velocity was spatially normalized. The percentage of filtered erroneous velocity data from the ADCP time series demonstrated a strong correlation with the surface concentration of mobile particles. In all experiments the normalized apparent velocities measured by the M9 corresponded well to the bedload velocity of the imagery data, better than those measured by the StreamPro, which appeared to underestimate the bedload velocity by a factor of 2-22. These deviations resulted from the different signal processing configurations, the acoustic geometry, and the immobile sediment bed. The backscattering (BS) strength was de-spiked and corrected by adapting the basic sonar equation for riverbed scattering. For the M9 the BS strength decreased as the bedload concentration increased, independently of the particle velocities and sizes. The BS strength registered by the StreamPro resulted in almost constant values for all transport conditions. Additional tests were performed using ultrasound velocity profilers developed by Ubertone. These results confirmed that the internal pressing and echo profiling resolution are crucial in the determination of the correct bedload velocity. The field experiments were conducted in two relatively large rivers in Germany (Oder and Elbe River) and in one small river in Albania (Tommorice River). Stationary measurements were performed using four different ADCPs (M9 Sontek, Rio Grande RDI 0.6 MHz and 1.2 MHz, RiverPro RDI 1.2 MHz) working at four different frequencies. The raw apparent bedload velocities were de-spiked and filtered in a stream-wise direction. Then, functional correlations were observed between the magnitudes of the apparent velocities and the bedload transport rates measured by pressure-difference bedload sampler. Each ADCP yielded different results because of the different frequency, backscatter sensitivity and acoustic penetration in the active bedload layer. In addition to the frequency, other acoustic parameters such as the percentage of the filtered data, transducers width, beamopening and grazing angle, the pulse length, contributed to the different acoustic bedload sampling. More precisely, the lower apparent bedload velocity was obtained when lower acoustic frequency, longer pulse lengths and larger beam focusing were used. The kinematic model was successfully applied for the middle frequencies (1.2 MHz and 1 MHz), which gave the best correspondence to the empirical estimation of the bedload active layer thickness…
Hydraulic Measurements & Experimental Methods Conference HMEM2017, 2017
The estimation of bedload velocity is notoriously difficult, particularly in field situations. Bi... more The estimation of bedload velocity is notoriously difficult, particularly in field situations. Bias of the bottom tracking (BT) mode of an acoustic Doppler current profiler (ADCP) due to moving bed material has been used many times to estimate the apparent velocity of the bed load. Herein we measure the bias of the BT signal due to bed load movement and calibrate this signal with some more certain measuring techniques. Specifically, this study explores several experiments under stationary conditions, where the signal of the ADCP BT mode is recorded and compared to the bed load motion measured by digital camera videography. The experiments were performed in the hydraulic laboratory of the University of Ottawa, using a SonTek M9 ADCP and two different cameras. Generally, a good matching has been documented between the averaged velocity of the moving particles measured by the ADCP and the videography. The slight deviation in single experiments can be explained by heterogeneity of the particles, difficulty in reproducing the same hydro-sedimentological conditions, and the randomness of scattering processes.
<p>The hydropower industry is facing serious challenges handling sediment h... more <p>The hydropower industry is facing serious challenges handling sediment hazards. In fact, the world’s total storage capacity is continuously decreasing 1-2% per year due to the sedimentation of reservoirs. The necessity to act accordingly, implies choosing the proper sediment management strategy, as early as in the design phase, and to adapt the system on the sediment and water discharge inflows during the operation of the hydropower plant (HPP). To achieve this goal, a detailed monitoring strategy must be implemented.</p><p>Periodic bathymetric surveys are crucial for obtaining reliable information about the sediment deposition. The Banje reservoir is located in Albania, in the Devoll river valley, which is a catchment with approximately 2000 t/ (km<sup>2</sup> year) sediment yield. The reservoir was commissioned in 2016 and until now two bathymetric studies were conducted. The measurements were performed using a single beam echosounder with dual frequency (80/200 kHz) and the RiverPro RDI, a five-beam acoustic doppler current profiler (ADCP): one vertical beam working at 600 kHz and four 1200 kHz slanted beam. In addition, 22 sediment samples were taken from the reservoir bottom with an Ekman grab sampler.</p><p>Both the echosounder and the ADCP are ultrasound instruments; besides the registering of water depth, they also give information about the strength of the returned acoustic signal (i.e., the backscatter). It is well known that the backscatter is highly sensitive to different roughness and river or reservoir bed composition of the reflecting material. In addition to the regular depth measurement, this study aims to correlate the density and particle size distribution of the bed sediment samples to the corrected backscatter signal. Furthermore, combining the observed changes of bed position and the investigated sediment characteristics, details about the total sediment deposition are inferred. The signal intensity from both instruments was corrected by applying an updated ultrasound equation, which yield the corrected backscatter signal. The first and the second returns (i.e., echoes) to the echosounder were used as an input data, whereas the ADCP bottom track signal strength indicator (RSSI) was included in the equation. The recorded raw data was previously processed and smoothed, carefully filtering errors and outliers.</p><p>A good correlation was obtained between the sediment samples density and the backscatter signal from the second echo. The ADCP backscatter is reasonably correlated to the particle size distribution of the bed material, but only for reflecting flat regions. The corrected first echo showed abrupt changes which are most likely produced by roughness variability of the reflecting region.</p><p>The combining of ADCP and single beam echosounder enabled a detailed analysis of the sediment characteristics and depositions in the reservoir. However further research is necessary to efficiently discard the false data reflected from submerged vegetation, buildings and debris. In addition, frequency dependent returns may be exploited to investigate the sediment layer consolidation.</p>
Symposium on River, Coastal and Estuarine Morphodynamics – RCEM2017, 2017
DESCRIPTION Climate change models uncertainty analysis are quite addressed in the literature, esp... more DESCRIPTION Climate change models uncertainty analysis are quite addressed in the literature, especially after each IPCC report. In fact, they o�fer comprehensive statistical information about the uncertainty of each GCM or RCM. In addition, the CC impact on the water resources is also well elaborated by numerous of studies and even governmental reports that o�er guidelines for CC mitigation and adaptation. After the AR5 was published, introducing the new concentration pathways and the new regional down-scaling framework EUROCORDEX, there are still no strong assessments and case studies that will asses the new approach and the uncertainty that follows. Over the decades, using Global Circulation Models to simulate future climate scenarios have been proved applicable and useful for depicting plausible future conditions and for climate change impact studies. However, given multiple GCMs simulations that are tuned to run under dif�erent assumptions (or initial conditions), a comprehensive uncertainty analysis is necessary in order to better understand those projected future conditions and its implications, as was done by IPCC in its Assessment Report. On the other hand, many studies on the climate change impact tend to use only a few projections within the impact assessment model, without justifying their choice of the scenarios. Moreover, small number of projections may also overlook the consequence due to the uncertainty in the GCM outputs. In this study we o�er a broad vision by investigating many up-to-date GCMs outputs available from latest IPCC project, and evaluate their impact on a complex water system within a decision-analytic modeling framework. The studies starts with a detailed statistical analysis of the projected temperature and precipitation. Followed by assessment of their impact on the water related activities in Lake Como basin as well as the downstream irrigation districts represented by Muzza. The speci�fic features of our approach, applied trough complicated multiple model simulations are: i.)In flow generation, ii.) impact quanti�fication based on a set of performance indicators, considering both upstream and downstream stakeholders; ii.)designing management polices, by meanings of optimal control techniques; iii.) preserving the multi-objective nature by Pareto Frontiers generation, evaluating the indicators and the uncertainty produced by di�ferent GCM/RCM combinations. After the application of suggested framework, the three con icting objectives are discussed under baseline, CC and co adaptive simulation. The water def�cit and the farmers pro�t are more likely to be highly impacted of the CC, while the flooding stands more inert for some projected results. While the analysis run, we discuss the "inner" uncertainty of the CC scenarios, and prove that is rather signi�cant. However the structural, modeling uncertainty is the most signi�ficant, despite the natural variability contribution is important and over cross with other sources of uncertainty. Notwithstanding the robustness of this analysis, we of�er a simple planning measure for successful mitigation and adaptation strategies facing the CC impacts.
Ascorbic acid (Vitamin C) was determined in four different tropical vegetables (Cucumber, Cabbage... more Ascorbic acid (Vitamin C) was determined in four different tropical vegetables (Cucumber, Cabbage, Spinach and Tomatoes) sourced from Yankaba market, Kano state. Colorimetric method was used for the determination. The ascorbic acid content in the cucumber, cabbage, spinach and tomatoes ranged from 51.67mgL-1 to 395.45mgL-1. Tomatoes were found to have the highest concentrations (395.45mgL-1) while cucumber has the lowest (181.82mg L-1 for the fresh and 60.00mgL-1 and 51.67mgL-1 respectively) for the dried vegetables. The deficiency of ascorbic acid is believed to result in scurvy, a disease characterized by spongy and sore gum, loose teeth, anaemia, swollen joint, fragile blood vessels. Frequent intake, therefore of these vegetables rich in vitamin C (especially tomatoes) will help prevent these problems in human being. This indicated that although the vegetables are rich in ascorbic acid content, their dried forms have grossly inadequate amount to ensure the provision of required dietary intake (RDI) of vitamin C for humans.
Water, 2020
Despite the many advantages of using active ultrasound sonars, recent studies have shown that the... more Despite the many advantages of using active ultrasound sonars, recent studies have shown that the specific acoustic geometry, signal-processing configuration, and complex surface-volume scattering process at the riverbed introduce several uncertainties in bedload estimation. This study presents a comparison of bedload velocity and bottom echo intensity measurements performed by monostatic and bistatic active ultrasound systems. The monostatic configuration is widely applied in the field to measure the apparent velocity at the riverbed with an acoustic current Doppler profiler (ADCP). Two laboratory investigations were conducted in two different hydraulic facilities deploying ADCP Stream Pro, monostatic and bistatic acoustic velocity profilers, manufactured by Ubertone. The bistatic instruments provided more accurate bedload velocity measurements and helped in understanding the acoustic sampling of the monastic systems. The bistatic profiles succeeded in measuring a profile over the ...
<p>Measuring and assessing the bedload data is a cr... more <p>Measuring and assessing the bedload data is a crucial for successful and efficient river management. Hence, the information about the bedload transport and characteristics helps to describe the dynamics of the river morphology and to evaluate the impacts on boat navigation, hydropower production, ecological systems and aquatic habitat.</p><p>Although the acoustic Doppler current profilers are designed to measure water velocities and discharges, they have been successfully used to measure some bedload characteristics, such as the apparent bedload velocity. The correlation between the apparent bedload velocity and the bedload transport rates measured by physical bedload samplers (e.g. pressure difference) has been examined and relatively high correlations have been reported. Moreover, laboratory experiments have proven that there is a strong correlation between the bedload concentration and particle size distribution and corrected backscattering strength obtained from the ADCPs.</p><p>The bedload transport rates yielded from the ADCPs outputs are usually derived as regression model-fitting of the measured apparent velocity and the physically collected bedload samples at the same time and position.  Alternatively, a semi-empirical kinematical approach is used, where the apparent bedload velocity is the main component and the bedload concentration is empirically estimated. However, the heterogeneous and sporadic motion of the bedload particles is often followed by high uncertainty and weak performance of these approaches.</p><p>Machine learning offers a relatively simple and robust method that has the potential to describe the nonlinearity of the complex bedload motion and so far, it has not been previously exploited for predicting transport rates. This study implements artificial neural network techniques to develop a model for predicting bedload transport rates by using only ADCP data outputs as training data. Data processing techniques are used to extract relevant features from the corrected backscattering strength and apparent velocity obtained from the ADCPs. More than 60 features were derived in the ADCPs dataset, and the most relevant features are selected through neighborhood component analysis. These features are used as inputs in conventional supervised neural network architecture which consists of two hidden layers and 35 neurons. This model is used to capture the distribution of the ADCP features for each output (e.g., physically measured transport rates and grain size from bedload samples) in the training sample. The back-propagation algorithm (BPA) is still one of the most widely used learning algorithms in the training process and thus herein applied. The learning rate, number of neurons and hidden layers were optimized by using Bayesian optimization techniques. The network was trained with more than 60 bedload samples and corresponding 5 - 10 min time series of ADCP preprocessed data. The rest of the samples were used for validation of the model. The validation resulted in correlation coefficients higher than 0.9 and the, which is significantly higher value than the corresponding values for the methodologies developed before. Aiming to develop a more robust and stable ANN model, further testing of different training algorithms must be performed, different ANN architecture should be tested, and more data shall be included.</p>
38th IAHR World Congress - "Water: Connecting the World", 2019
This study aims to develop a surrogate methodology for quantification of the bedload transport in... more This study aims to develop a surrogate methodology for quantification of the bedload transport in riverine environments by using acoustic devices. Bedload transport experiments were performed in laboratory conditions to test the capabilities of the acoustic current Doppler profilers (ADCP) to quantify the bedload velocity, concentration, and active layer thickness. Two ADCPs working at four frequencies (0.5MHz, 1MHz, 3MHz M9, by Sontek, and 2MHz StreamPro, by RDI) were deployed at the same time. Simultaneously, the bedload transport was monitored by high-speed cameras, and continuous bedload transport rate measurements were conducted at the end of the measurement section. The apparent bedload velocity was analyzed and compared with the velocity from the imagery data and the transport rates measured by the bedload trap. Besides the apparent bedload velocity, the ADCPs also registered the backscattered (BS) signal from the sediment bed, which appeared to be sensitive to the change of the bedload transport conditions and the type of the sediment particles. The results confirmed the capability of these acoustic instruments to measure the bedload velocity by demonstrating a strong correlation with the physical transport measurements and the velocities from the imagery data. The apparent velocities measured by the 3 MHz and 1 MHz demonstrated similar results; the 2 MHz measurements led to lower values with 2-4.5 times magnitude difference comparing with the spatially normalized image velocity. The corrected BS signal documented a clear correlation with the apparent bedload velocity, more precisely with the change of the bedload transport condition. The variation between the results from the two instruments is assigned to the different acoustic geometry of the instruments, internal processing, and availability of the instrument related parameters needed for correction of the backscattered signal. Future tests should aim towards a better understanding of the internal processing of the signal and extensive analysis of BS strength sensitivity towards a wide range of sediment types and hydraulic conditions.
Journal of Hydraulic Research, 2020
ABSTRACT This paper provides an evaluation of a hydro-acoustic technique for efficient quantifica... more ABSTRACT This paper provides an evaluation of a hydro-acoustic technique for efficient quantification of the bedload transport in riverine environments. Stationary bedload measurements were conducted simultaneously at different study sites, using three different acoustic Doppler current profilers (ADCP) working at four different frequencies. The raw apparent bedload velocities were de-spiked and filtered in a streamwise direction. Then, functional correlations were observed between the magnitudes of the apparent velocities and the bedload transport rates measured by the conventional bedload sampler. Each ADCP yielded different results because of the different frequency backscatter sensitivity and acoustic penetration in the active bedload layer. In addition to the frequency, other acoustic parameters such as the percentage of the filtered data, transducers width, beam opening angle, beam-grazing angle and the pulse length, contributed to the acoustic bedload sampling. The influence of these parameters is examined, and recommendations are given for the performance and limitations of each instrument.
E3S Web of Conferences, 2018
The bottom tracking (BT) feature of the acoustic Doppler current profilers (ADCP) have emerged as... more The bottom tracking (BT) feature of the acoustic Doppler current profilers (ADCP) have emerged as a promising technique in evaluating the bed load. Strong statistical correlations are reported between the ADCP BT velocity and the transport rate obtained by physical sampling or dune tracking; however, these relations are strictly site-specific and a local calibration is necessary. The direct physical sampling is very labor intensive and it is prone to high instrument uncertainty. The aim of this work is to develop a methodology for evaluating the bed load transport using commercial ADCPs without calibration with physical samples. Relatively long stationary measurements were performed in a sand-bed and sand gravel rivers, using three different ADCPs working at 3MHz, 1.2MHz and 0.6MHz. Simultaneously, bed load samples were collected with physical samplers, and the riverbed was closely observed with digital cameras mounted on the samplers. It is demonstrated that the kinematic transport...
Journal of Hydraulic Engineering, 2019
AbstractSeveral studies have investigated the use of the bottom tracking (BT) mode of acoustic Do... more AbstractSeveral studies have investigated the use of the bottom tracking (BT) mode of acoustic Doppler current profilers (ADCPs) for evaluating bedload transport. The raw apparent bedload velocity ...
DESCRIPTION Climate change models uncertainty analysis are quite addressed in the literature, esp... more DESCRIPTION Climate change models uncertainty analysis are quite addressed in the literature, especially after each IPCC report. In fact, they o�fer comprehensive statistical information about the uncertainty of each GCM or RCM. In addition, the CC impact on the water resources is also well elaborated by numerous of studies and even governmental reports that o�er guidelines for CC mitigation and adaptation. After the AR5 was published, introducing the new concentration pathways and the new regional down-scaling framework EUROCORDEX, there are still no strong assessments and case studies that will asses the new approach and the uncertainty that follows. Over the decades, using Global Circulation Models to simulate future climate scenarios have been proved applicable and useful for depicting plausible future conditions and for climate change impact studies. However, given multiple GCMs simulations that are tuned to run under dif�erent assumptions (or initial conditions), a comprehensi...
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Papers by Slaven Conevski