Fluorescent Sand Research Articles

Engineering of ethylenediamine-functionalized 0D carbon dots for optical bi-mode determination of Hg(II), fluorescent sand, and logic gate operations

A sensitive photoluminescence turn-off Hg(II) sensor based on ethylenediamine-functionalized carbon dots (CDs/en) fabricated using wastepaper and ethylenediamine via a facile two-step synthesis process. A quantum yield (QY) obtained is 16.2 % with maximum emission at 446 nm. The CDs/en acted as the blue fluorescent probe accompanied by strong quenching of the fluorescence emission with Hg(II) at pH 6. The amino or oxygen groups on the CDs/en allow electron transfer to Hg(II), leading to fluorescence quenching. Under the optimal condition, the proposed sensor was applied to detect Hg(II) in the linear range of 1–20 nM. A detection limit of 0.16 nM is achieved using fluorescence spectroscopy and 0.72 nM by monitoring the absorbance variation at 274 nm. The successful real sample analysis and “EXIT” signs made of fluorescent sand also paved the way for the best optical sensor. Based on the bi-mode signals, a “NAND” logic gate was constructed effectively.

Assessment of plot-scale sediment transport on young moraines in the Swiss Alps using a fluorescent sand tracer

Abstract. Glacial retreat uncovers large bodies of unconsolidated sediment that are prone to erosion. However, our knowledge of overland flow (OF) generation and sediment transport on moraines that have recently become ice-free is still limited. To investigate how the surface characteristics of young moraines affect OF and sediment transport, we installed five bounded runoff plots on two moraines of different ages in a proglacial area of the Swiss Alps. On each plot we conducted three sprinkling experiments to determine OF characteristics (i.e., total OF and peak OF flow rate) and measured sediment transport (turbidity, sediment concentrations, and total sediment yield). To determine and visualize where sediment transport takes place, we used a fluorescent sand tracer with an afterglow as well as ultraviolet (UV) and light-emitting diode (LED) lamps and a high-resolution camera. The results highlight the ability of this field setup to detect sand movement, even for individual fluorescent sand particles (300–500 µm grain size), and to distinguish between the two main mechanisms of sediment transport: OF-driven erosion and splash erosion. The higher rock cover on the younger moraine resulted in longer sediment transport distances and a higher sediment yield. In contrast, the higher vegetation cover on the older moraine promoted infiltration and reduced the length of the sediment transport pathways. Thus, this study demonstrates the potential of the use of fluorescent sand with an afterglow to determine sediment transport pathways as well as the fact that these observations can help to improve our understanding of OF and sediment transport processes on complex natural hillslopes.

Transport of heterometric sediments in wave-dominated flows – Tracer experiments

Sediment dynamics is a complex subject, playing an important role in coastal areas. The interaction between wave action and sediment particles is determinant to understand sediment transport processes. The knowledge of sediment transport comprising sand mixtures is relevant as coastal areas, usually, present heterogeneities of sediment particle sizes in the horizontal and vertical directions, denoting the existence of selective transport processes. This study investigates the effects of non-cohesive size-graded sands on sediment transport fluxes to understand selective transport mechanisms under wave-dominated conditions. A laboratory experiment was carried out at the large wave flume (Großer Wellenkanal, GWK) in Hannover, considering distinct sediment mixtures between two well-sorted sands with median grain sizes of 0.21 mm and 0.58 mm. The experiments were carried out for four sediment bed configurations with two different wave energy conditions. A fluorescent sand tracer technique was implemented to measure total and fractional net sediment transport rates and the outcomes are compared with the ones obtained with the mass conservation method. The experimental results show the occurrence of the interaction between different sand fractions: a decrease in the transport of fine sediments and an enhancement of the transport of the coarse sediments as the percentage of coarse sediments in the bed mixture increases. These effects are larger as the coarser fraction in the sand bed increases and they are noticeable for different sediment transport regimes (sheet flow and rippled beds).

Laboratory modelling of vertical sediment mixing in the surf zone

ABSTRACT A comprehensive set of laboratory experiments were conducted to investigate the spatial distributions of mixing depth in the surf zone. A wooden sandbox of 0.15-m-deep and 1.0-m-long is fabricated and placed in the middle of the bed slope. In the experiments, five different sediment diameters were used and the same diameters of fluorescent sand tracers were sprinkled on the sand bed surface to investigate the mixing depth. After a specific duration of regular wave generation , core samples were taken at six different cross-shore locationsand analyzed the mixing depth. Moreover, the flow velocity field in the surf zone was obtained by using a Large Eddy Simulation model and discussed the relationship with spatial distributions of mixing depth. The results reveal that the mixing depth has cross-shore spatial variation and the maximum mixing depth occurred at the impinging point for all tested sediment diameters. The spatial distributions for each diameter were repeatable; however, the depth decreases in a logarithmic manner from smaller to larger grain size. Furthermore, the spatial distribution of mixing depth is correlated with the bottom root mean square vertical velocity and proposed a new simple mathematical relationship for mixing depth that shows good accuracy with experimental data.

Ln3+(Eu3+/Tb3+)-hybridized fluorescent sands with smart self-cleaning property for outdoor photonic indicators (OPIs)

In this work, we developed Ln3+(Eu3+/Tb3+)-hybridized fluorescent sands with self-cleaning properties for outdoor photonic indicators (OPIs). To introduce Ln3+(Eu3+/Tb3+)-induced fluorescence sand-surfaces with superhydrophobic properties, Ln3+ complexes (EuC/TbC) were anchored to sand@SiO2 particulates for the formation of sand@SiO2@LnC@PFDS. The emission spectra were measured at 365/345 nm for sand@SiO2@EuC@PFDS and sand@SiO2@TbC@PFDS. Sand@SiO2@LnC@PFDS indicated highly bright red and green emission with a long fluorescence lifetime. CIE color data were used to evaluate the high color purity of the red/green emissions under ultraviolet excitation light. More importantly, fluorescent sand particulates with self-cleaning properties can prevent intense photonic signals from being polluted by dust, ice, humidity, and rainwater which can be applied to construct signaling indicators for emergency rescue work and natural disaster sites.

Sediment Transport with Mixed Sand in Nonlinear Regular Waves

Ferreira, C.C.; Abreu, T.; Silva, P.A.; Bernabeu, A.; Romao, S., and Staudt, F., 2020. Sediment transport with mixed sand in nonlinear regular waves. In: Malvarez, G. and Navas, F. (eds.), Global Coastal Issues of 2020. Journal of Coastal Research, Special Issue No. 95, pp. 408–411. Coconut Creek (Florida), ISSN 0749-0208.This work presents the results of an experiment carried out in the Large Wave Flume (Groser Wellenkanal, GWK) in Hannover, which enables full-scale wave experiments to be conducted above sand beds. The experiment consisted of a set of regular waves propagating over a 30 m long horizontal bed composed of a bimodal mixture of fine (F) and coarse (C) sands. Wave gauges placed along the test section and an ADV (Acoustic Doppler Velocimeter) placed above the wave bottom boundary layer allow characterizing the wave nonlinearity parameters (skewness and asymmetry). Fluorescent sand was inserted at the beginning of each experiment and subsequent bed samples allowed tracking its movement, differentiating between the coarse and fine sand fractions.This study presents the results obtained with a particular sediment mixture (75%F+25%C) for two regular trochoidal wave conditions with the same wave period, 7 s, but different wave heights, 1.0 and 1.5 m. The total net transport rates estimated from a practical sediment transport formula, which includes both effects of wave asymmetry and skewness, are comparable with those obtained with the fluorescent tracer.

Sediment particle movements observed using tracers under accretive wave conditions in the nearshore zone

ABSTRACTField observations were conducted during relatively mild wave conditions at a dissipative barred sandy beach to investigate the cross-shore sediment dynamics from the inner surf zone to the offshore side of the outer bar. Fluorescent sand tracers of five different colors were placed on the seabed at different cross-shore locations, and sand core samples were extracted respectively 11 and 20 days after the placement of tracers. Moreover, nine cross-shore bathymetric/topographic beach surveys were conducted, and the water level, wave, and wind conditions were observed. The objective of this research was to investigate the mechanisms of the on- and offshore-directed sediment transport during the inner- and outer-bar accretion events. The analyzed results revealed that at the inner surf zone, the sediment was dominantly transported in the onshore direction. The sediment was also transported offshore-ward due to the undertow; however, this occurred until the offshore end of the trough region. Overall, the outer bar shape affected the on-offshore sediment transport rate. The sediment movements in the onshore region and offshore region of the outer bar were not related; however, the outer bar was formed with the sediments from both the inner- and outer-bar regions.

Observation of Sediment Dynamics in the Nearshore Region using Fluorescent Sand Tracers

The field observations of cross-shore sediment transport from the swash zone to the offshore side of the outer bar using fluorescent sand tracers were conducted in 2014 and 2015 at the Hasaki coast, Japan facing the Pacific Ocean during storm wave conditions. The topography difference between the two years data set is that outer bar shape existed in 2014 and not existed in 2015. During the observations, wave height and wave period were observed, and sand core samplings were conducted. By using the observed wave data and the analyzed results of collected fluorescent sand tracers from the cores, the sediment movements from the offshore side of the outer bar area to the swash zone during storms were investigated. The results indicate that the sediment movements during the storms were affected by the outer bar shape. If the outer bar existed, the sediment of the onshore side of the outer bar tend to move landward, and it also moves to seaward due to undertow until the outer bar location. The sediment at the offshore side of the outer bar tends to move to onshore ward due to bedload sediment transport. However, the transport rate decrease in the trough region. The beach topography without the bar shape, the bed load sediment transport rate at the trough region was higher than that with the bar shape. Thus, the sediments at the offshore side of the bar also could move until the swash zone.

OBSERVATIONS OF SEDIMENT PARTICLE MOVEMENTS UNDER ACCRETIVE WAVE CONDITIONS

From the aspect of beach management, understanding of sediment movement from the outer-surf zone to the swash zone during recovery duration is important. In this study, field observations were conducted during accretive wave conditions to investigate the sediment movement from the outer side of the bar to the swash zone using fluorescent sand tracers.

Uncertainties in assessing tillage erosion – How appropriate are our measuring techniques?

Tillage erosion on arable land is a very important process leading to a net downslope movement of soil and soil constitutes. Tillage erosion rates are commonly in the same order of magnitude as water erosion rates and can be even higher, especially under highly mechanized agricultural soil management. Despite its prevalence and magnitude, tillage erosion is still understudied compared to water erosion. The goal of this study was to bring together experts using different techniques to determine tillage erosion and use the different results to discuss and quantify uncertainties associated with tillage erosion measurements. The study was performed in northeastern Germany on a 10m by 50m plot with a mean slope of 8%. Tillage erosion was determined after two sequences of seven tillage operations. Two different micro-tracers (magnetic iron oxide mixed with soil and fluorescent sand) and one macro-tracer (passive radio-frequency identification transponders (RFIDs), size: 4×22mm) were used to directly determine soil fluxes. Moreover, tillage induced changes in topography were measured for the entire plot with two different terrestrial laser scanners and an unmanned aerial system for structure from motion topography analysis. Based on these elevation differences, corresponding soil fluxes were calculated. The mean translocation distance of all techniques was 0.57m per tillage pass, with a relatively wide range of mean soil translocation distances ranging from 0.39 to 0.72m per pass. A benchmark technique could not be identified as all used techniques have individual error sources, which could not be quantified. However, the translocation distances of the macro-tracers used were consistently smaller than the translocation distances of the micro-tracers (mean difference=−26±12%), which questions the widely used assumption of non-selective soil transport via tillage operations. This study points out that tillage erosion measurements, carried out under almost optimal conditions, are subject to major uncertainties that are far from negligible.

CHARACTERISTICS OF SEDIMENT TRANSPORT IN SWASH ZONE DUE TO SATURATED-UNSATURATED SLOPED BEACH

The influence of saturated-unsaturated sloped beach on sediment transport in swash zone is investigated experimentally and numerically. The movement of fluorescent sand on seabed and the orbit of fluorescent paint injected into sandy beach are measured in bore wave experiments. As the result, the uplift seepage flow leads to the activation of sediment transport in the direction of run-up and backwash under the saturated slope. The numerical modelling simulates the interacting swash wave motion and saturated-unsaturated coastal seepage flow. The tractive force under the influence of seepage flow is quantified through a permeable Shields parameter. The results of prediction are in good qualitative agreement with those of experiments.

Super-hydrophobic “smart” sand for buried explosive detection

Explosive-sensitive fluorescent sand (“smart” sand) was prepared through the simple coating of polystyrene/pyrene/TBAHP composite on normal sand. The as-prepared “smart” sand was characterized using SEM, EDS, XRD, FT-IR, Raman, and UV-Vis. Further analysis of contact angle and fluorescence emission spectra confirm that the explosive-sensitive fluorescent composite film coats on the surface of the sand, endowing “smart” sand both strong fluorescence and super-hydrophobicity, which provides an excellent sensing material for buried nitroaromatic explosive sensing, presumably due to its strong affinity with nitroaromatic explosive vapor. The detection of buried explosives in soil was achieved and validated through quenched spots on a thin layer of “smart” sand paved on the top of soil. The quenched area and decreased intensity vary with the amounts and depths of 2,4-DNT buried in soils. Such detection can be performed using a handheld UV lamp and observed by naked eyes, thus providing great potential and advantage for large-scale landmine detection and mapping.

Evaluation and Verification of the Effect of An Examination of Beach Nourishment Focused on the Grain Size

The effect of the beach nourishment on the Yamamoto coast which has been suffering from serious beach erosion was evaluated. From the fluorescent sand survey even medium sand with diameter of about 0.3mm passed over the headland in coming of significant waves higher than 2m. About 80% of sand particles moved out from the injection point within 1 year. According to the Bruun equation, the profile of this beach was identified as the concave and eroded type. Sediment survey showed that sand particles larger than 0.25mm stayed in shallow area with depth less than 2m and remained there for more than 1 year. In addition, Numerical model built to estimate the effectiveness of different grain size on beach nourishment demonstrated availability of gravels for effective nourishment.

Sediment Transport along the Coast of Israel: Examination of Fluorescent Sand Tracers

Abstract The method of labeled natural sand particles was used to study sediment transport along the central Mediterranean coast of Israel. Six portions of 300 kg each were tagged with various fluorescent colors, and distributed at six different locations in the vicinity of the Herzliya Marina. The tagged sand was scattered at the end of autumn, and sampled three times during the winter. Sampling was interrupted in mid-January because of unexpected dredging at the marina canal entrance. The samples were analyzed at the Yigal Allon Kinneret Limnological Laboratory. The wave climate during that time was analyzed using wave data from Ashdod (40 km south). Wave directions measured in Ashdod were corrected to make them applicable to the Herzliya coast, in accordance with suggested directional shift values. Seven wave storms with significant wave heights of over 2.5 m were observed. Two of them clearly indicate a dominant direction from the southwest and two others from the northwest. However, the time duration...

Evaluation of Longshore Transport Equations with OBS Sensors, Streamer Traps, and Fluorescent Tracer

Abstract Measurements of longshore sediment transport rate were conducted on a reflective to intermediate sandy beach during energetic sea breeze activity. The suspended load transport was obtained with optical backscatter sensors, current meters, and streamer traps, whereas the total load rate was measured with fluorescent sand tracer. The streamer trap measurements revealed an exponential vertical distribution of the suspended sediment flux, with the degree of vertical mixing decreasing in the onshore direction. A continuous time series of longshore suspended sediment flux across the surf zone was obtained by combining streamer trap measurements with data collected with surf zone instruments. Comparison of the suspended longshore flux with the total longshore flux derived from the dispersal of fluorescent tracer indicated that the relative contribution of suspended load to total load was ca. 35%. The movement of sand tracer further demonstrated that nearshore sediments were transported obliquely across ...

Offshore sand bank dynamics

The present paper reports some key results from field investigations and numerical modelling studies of the tide- and wind-induced hydrodynamics and sediment dynamics of Middelkerke Bank (MB) in the southern North Sea of Europe conducted during December 1992 to March 1993. Strong surface current refraction and acceleration effects were observed over MB using the HF radar system OSCR ( Ocean Surface Current Radar). Results suggest that OSCR data may be used remotely to monitor large-scale bathymetry in shallow coastal environments. Spatial variation in tidal propagation characteristics and modification of shoreward propagating waves was not detected at locations around MB during the experiment. Observed residual currents were found to be correlated strongly with wind speed and direction during the period 26 February to 18 March 1993. However, in low wind stress condition, a three-dimensional numerical model (3D-Bank) indicated the presence of a clockwise residual circulation of water around MB consistent with theory. Spatial and temporal variation in the average total drag coefficient ( C d) of MB were investigated and found to correlate strongly with tidal current speed. Fluorescent sand tracers, used to monitor net sediment transport pathways, revealed a net clockwise movement of sediments around MB consistent with predictions by 3D-Bank and with theory.

Dynamics of some Alexandria beaches as predicted by fluorescent sand experiments, Egypt

Dynamics of some Alexandria beaches as predicted by fluorescent sand experiments, Egypt

Fluorescent sands for measurements of longshore transport rates: a case study from Praia de Faro in southern Portugal

A field experiment was carried out on a mesotidal reflective beach to relate longshore sand transport rates to wave measurements in medium-energy conditions (H rms =0.6 m; T m =6.5 sec; α=20°). Dispersion of fluorescent sand tracers was analyzed using the spatial integration method (SIM). The measured sand transport rate was three times larger than the prediction computed using the longshore wave power approach, while the K factor was determined empirically as 2.32. The study concluded that there is a need to calibrate bulk longshore transport predictors before applying them to steep gradient slopes under plunging waves.

Measurement of sand transport by spatial method with fluorescent sand tracer along the Damietta promontory, Egypt

Measurement of sand transport by spatial method with fluorescent sand tracer along the Damietta promontory, Egypt

Water and sediment movement in the vicinity of linear sandbanks: the Norfolk Banks, southern North Sea

Geophysical surveys, current meter measurements and fluorescent sand tracer experiments were undertaken in the vicinity of the Broken Bank. The data are used to establish localised and regional patterns of water and sediment movement. The results obtained confirm mechanisms proposed previously for sandbank growth, with particular reference to the North Sea; these include the clockwise circulation of water and sand, with convergence at the crestline. Secondary helical water circulations do not appear to be a dominant process influencing sandbank maintenance. However, such circulation may still be important in the initial formation of linear sandbanks and/or at some stages in the bank development. On a regional basis, residual currents, bedform asymmetries and tracer dispersion indicate an offshore sediment transport component. This observation supports the hypothesis of other investigators, formed on the basis of geomorphological observations and numerical model predictions, concerning the movement of sand under extreme conditions. Moreover, these transport pathways may persist under low wave and tidally-dominated conditions, as opposed to being restricted to storm activity.