Fluorescent Sand Research Articles

Particle and fluid bioturbation caused by the priapulid wormHalicryptus spinulosus(v. Seibold)

Abstract The priapulid worm Halicryptus spinulosus was found with a density of about 60 ± 20 ind m-2 in the silty sediment of Kiel Bight (western Baltic). In sediment samples taken by a box corer we found a burrow system down to 25 cm sediment depth, connected with the overlying water by openings at the sediment surface. In this 25 cm sediment depth the volume of the burrow systems was estimated to be 0.35 %, which corresponds to a secondary surface of 0.7 m2 for each 1 m2 sediment surface. Laboratory experiments, using fluorescent sand grains (luminophores) as particle tracers and sodium bromide as a tracer for dissolved compounds, were performed to quantify the bioturbative effects of H. spinulosus. Results from laboratory experiments indicate a downward particle transport, strongly correlated with H. spinulosus abundance and number of burrow openings. From these experiments a bulk sediment transport time, i.e. the time in which the uppermost (2 mm) sediment layer is completely mixed into a distinct sed...

Hydrodynamics and sediment dynamics of North Sea sand waves and sand banks

Seabed drag coefficients have been measured at a site within the Norfolk Banks and at a site within the sand wave field in the southern North Sea, using pressure sensors and moored current meters. At the sand banks site a seabed tripod measuring turbulent flows within 1 m of the bed was also used. The results are generally in agreement with values used in numerical models. At the sand banks site, the drag coefficient increases with wind conditions, but at the sand waves site there is a reduction during the highest wave conditions, attributed to the drag reduction caused by sand resuspension from the bed. This result suggests that sediment effects must be considered if wave/current interaction is included in numerical models of the region. The drag coefficient for reversing tidal flows over the asymmetric sand waves is found to be larger for flow towards the steeper face, suggesting a small form drag component. Studies of sand movement used bedform mapping, fluorescent sand tracing and photography of migrating ripples. There is evidence for the early stages of formation of a new bank between Broken Bank and Well Bank. At the sand waves site, ripple migration is found to be a useful estimator of bedload transport under conditions of negligible suspension. Over the sand banks, a definite correlation of surface water properties, notably the turbidity, with the topography of the banks was observed. The mechanism for this surface effect is not known but it is consistent with the observation of features, seen in satellite visible light images, which outline the shapes of the banks.

Morphology, sedimentary bedforms and sand transport across a ridge- and- runnel beach under the action of summer waves

As part of a collaborative study between the 3rd Institute of Oceanography, Xiamen, and the U. K. Universities of East Anglia and St. Andrews, a 4-day experiment was conducted on a ridge- and- runnel beach of north Norfolk on the North Sea coast. Detailed surveys were made of every low water of an area 10m by 30m and electromagnetic current meters were used to measure wave-induced currents over the ridge and in the runnel. The locations of bedform fields were noted, fluorescent sand was used to follow the sand movement and, at the end of the experiment, lacquer peels were taken of the top 0.2m of a vertical section through the ridge- and- runnel.

LOCAL MOVEMENTS OF SAND IN THE SURF ZONE

The fluorescent sand tracers are injected in a point in the surf zone. Core samples are taken from the sixteen points on the circumference with the time intervals of fifteen minutes for about five hours. At the same time, the horizontal two components of fluid velocities are measured at the injection point by using an electromagnetic currentmeter. The field observations have been carried out three times on two beaches facing to the Pacific Ocean. The relations between the local sand movements and the fluid dynamics are examined on the basis of the data obtained.

砂質浅海底における砂れん型と砂移動

Sand ripples formed by waves on a sandy shallow sea bottom are classified into regular parallel ripples, nearshore irregular parallel ripples, diagonal ripples and lunate ripples. They are arranged in this order from offshore to onshore regions. The difference of sand movement mode would probably exist among these ripple types. The purpose of this study is to describe the difference of sand movement on each ripple type in connection with the ripple geometries and the characteristics of wave-induced oscillatory water flows near the sea bottom. Field investigations were performed on a shallow offshore zone at Tatado Beach, Izu Peninsula, Japan (Fig. 1), in July and October 1979. The mode of sand movement was first observed, and then the direction of net sand drift was investigated by use of fluorescent sand composed of four ranges of grain size (i.e., -1-0φ, 0-1φ, 1-2φ, and 2-3φ) with different colors. Wave-induced oscillatory flows were measured using an ultrasonic current meter installed at a height of 36cm above the sea bottom. Three types of sand movement were observed on a rippled bed: Type I: sand movement in traction mode, Type II: sand movement closely relating to vortices formed in ripple troughs, and Type III: sand movement in the form of suspended sand cloud which entirely covers the sea bed. Type I is suitable for coarser sand transport, while Type II sand movement is for finer sand. Type III contributes to the transport of material which can be suspended by the oscillatory water flows. The result of measurement of oscillatory water flows showd that onshore velocity was stronger than offshore velocity on any type of ripples. In such a velocity field, Type I and III give rise to a net onshore sand drift, while Type II produces an offshore net drift due to the existence of vortices. A prevailing sand movement mode is different on ripples with different types. Consequently, the direction of net sand drift for various size of sand grains is different for each type of ripples (Table 2).

Sand transport under the combined influence of waves and tidal currents: An assessment of available formulae

Various formulae are used to predict the transport of sand under the combined influence of waves and currents. These approaches include the use of the unidirectional formulae of Einstein (1950), Frijlink (1952), Yalin (1963), Engelund and Hansen (1967), Sternberg (1972), Ackers and White (1973) and Gadd et al. (1978) modified, for the presence of waves, in accordance with the techniques described by Bijker (1967) and Swart (1976) and those of Bagnold (1963), Madsen and Grant (1976) and Vincent et al. (1981). Predicted rates are compared with measurements, based upon fluorescent sand tracer studies, in an area of high tidal current and wave energy (northern Bristol Channel, U.K.). In general, predicted rates are lower than those measured and only the formulae of Madsen and Grant (1976) and the modified formula of Sternberg (1972) appear to provide realistic estimates of transport under wave- and tidally induced currents, in comparison with the field measurements.

Sediment transport under waves and tidal currents: A case study from the northern Bristol Channel, U.K.

Bed-load transport under tidal currents and waves, and waves alone, is predicted from near-bed self-recording current-meter data and observations from a wave-rider buoy. Transport rates and paths are derived using seven different unidirectional transport formulae and those of Bagnold (1963), Bijker (1967) and Madsen and Grant (1976) for combined flows. Predicted rates are compared with the results of a fluorescent sand tracer study. The data are available from Swansea Bay, a high tidal- and wave-energy embayment on the British continental shelf. Sediment transport paths in this region had been determined previously using a variety of techniques, including bedform orientation and sea-bed drifter recovery patterns. Transport is enhanced under the superimposed effect of waves and, in some circumstances, the direction of the resultant vector is altered. Such storm-induced catastrophic transport is different to that predicted under tidal currents alone; this could provide a mechanism for long-term sediment supply. In some areas, there is correspondence between bedform orientation and storm-induced transport paths; in others, there is opposition.

FIELD EXPERIMENTS ON LONGSHORE SAND TRANSPORT IN THE SURF ZONE

Eight fluorescent sand tracer experiments were performed in energetic surf zones on natural beaches and on beaches near structures to measure the short-term longshore sand transport rate. Tracer of up to four distinct colors was injected on a line crossing the surf zone to investigate the on-offshore distributions of the longshore sand adveetion velocity and transport rate. The tracer advection velocity, v , and the depth of mixing into the bed, b, were determined from large numbers of cores taken in situ throughout the sampling area. The sand advection velocity and mixing depth were not constant across the surf zone, but usually exhibited a maximum either toward the shoreline or toward the breaker line, or in both regions. The local breaking wave height, H. , and horizontal current velocity in the surf zone (yielding an average longshore current velocity V) were also measured. The data were interpreted with simple dimensional arguments to give the following results: b = 0.027 H,, v = 0.011 V, and the volumetric transport rate Q = 0.024 H V. Agreement was also found between the measured total longshore sand transport rate and a predictive expression due to Bagnold involving the breaking wave power and average longshore current velocity. Although the results appear reasonable and consistent, a problem remains concerning the apparent decrease in tracer advection speed alongshore recorded in most experiments at the longer sampling times.

A new technique for injecting fluorescent sand tracer in sediment transport experiments in a shallow water marine environment

A new method is described for the rapid injection of large quantities of fluorescent tracer sand onto the seabed in water up to 10 m or so deep. It has been used successfully in bedload sediment transport measurements, giving quantitative results comparable with those employing radioactive tracer. In particular the tracer was detected in significant quantities for more than half a year after injection.

Sediment Dispersal at Fort George Inlet, Florida: ABSTRACT

Fort George Inlet is located in northeastern Florida, 0.9 km north of the St. Johns River. The geomorphic history of Fort George Inlet is characterized by migration. The pattern and rate of sediment dispersal were established through fluorescent sand tracing, tidal-current measurement, and bed-form mapping. Morphologic changes were determined utilizing nearshore and beach profiles established in 1923 and 1974, as well as air photos, hydrographic surveys, historical maps, and coastal climate data. Fort George Inlet partially intercepts the southerly littoral drift (estimate of 190,000 m3/year based on SSMO data) and deposits sediment along Little Talbot Island and Wards Bank, altering the hydrodynamic system in the study area. In the past, accretion at Little Talbot Island (average rate of 142,880 m3/year) forced Fort George Inlet south at an average rate of 36 m/year. However, in 1961 the direction of inlet migration was reversed and is now northward at a rate of 21 m/year. Sediment intercepted by Fort George Inlet is producing a recurved spit extending north from Wards Bank. The expansion and encroachment of this spit into the inlet throat are believed to have initiated the reversal in migration direction. Analysis of aerial photographs indicates that in et migration occurs sporadically during severe storms. End_of_Article - Last_Page 508------------

DEPTH OF DISTURBANCE OF SAND IN SURF ZONES

A coring technique employed during wave action allowed accurate measurement of the depth of vertical mixing bm of fluorescent sand tracer grains within the surf zone of a gently sloping Pacific Ocean beach (beach slope tangent s = 0.012). The depth bm is the distance from the sediment surface to the lower limit of observed tracer grains within the inner portion of the core. Although this definition is only strictly applicable to a rectangular distribution of tracer concentration with depth, the bm results were quite similar to those using concentration-weighted depth averages of Crickmore (1967). For one winter regime experiment, vertical cross-sectional contour maps of tracer concentration normalized by the local core maximum were drawn with concentrations computed for each 0.4cm slice. Trends present are (1) in the onshore-offshore direction the maximum concentration is at the bed surface shorewards of the mid-surf position and 0.4 cm to 1.2 cm below the bed seaward of the mid-surf position, and (2) in the longshore direction (at the mid-surf position) the maximum concentration lies 0.4 cm to 1.6 cm below the bed surface. For spilling breaker heights Hb between 75 cm and 150 cm, histograms of bm were clearly different for spring/summer and fall/winter experiments: the mean and standard deviation (in parenthesis) are 0.5 cm (0.5 cm) and 1.1 cm (0.5 cm), respectively. These results are substantially less than both the 3.0 cm and the 20 cm to 40 cm disturbance depths per 100 cm of Hb reported by King (1951) and by Otvos (1965) and Williams (1970). The discrepancy with Otvos and Williams is due to the much different breaking process; in their experiments small breakers (Hb = 5 cm to 30 cm) plunged directly onto steep beach slopes (s = 0.1) causing large bm- The tracer grain's longer exposure to bottom stresses of passing surf bores may explain King's greater disturbance depths. Her sampling interval was one semi-diurnal tidal period T versus the span 0.02 T to 0.32 T in this study.

Selective Longshore Transport Rates of Different Grain-size Fractions within a Beach

ABSTRACT Measurements were obtained at El Moreno Beach, Mexico, of the longshore transport rates of different grain sizes found within the beach sand. The rates were determined through the use of fluorescent sand tracers, but unlike previous studies of selective grain sorting, the entire grain-size distribution was tagged with only one color. By sieving the grid samples obtained downdrift from the tracer injection location into their several size fractions and counting the number of tracer grains in each, one obtains transport patterns for each of the individual grain-size fractions. The first moment of the tracer concentration about the injection line yields the mean longshore transport distance and thus the mean transport velocity for each grain-size fraction found in the beach sand. The measurements show that the coarsest sand grains found within the beach, the fraction centered at 1.19 mm, moved alongshore the fastest with a mean advection rate of 0.31 cm/sec. This rate is about four times faster than grains of diameter 0.30 mm. The results substantiate the conclusions arrived at by Evans in 1939 on Lake Michigan beaches that the finer sand grains swash high up the beach face where they move alongshore more slowly than the coarser grains that remain near the breaker zone and are transported by stronger longshore currents.

FIELD INVESTIGATION OF SEDIMENT TRANSPORT PATTERN IN A CLOSED SYSTEM

In order to elucidate the transport pattern of sediment in a closed system, a pocket beach was chosen and investigated from various aspects. This investigation included the following studies: (1) bathymetric survey by an echo sounder, (2) survey of submarine geology using an acoustic probe, (3) observation of nearshore current systems using floats, (4) documentation of the transport pattern of suspended sediment by aerial photographs, (5) examination of depositional environments of bottom and beach material by sieve analysis, (6) inference of long-term alongshore sediment transport pattern from the grain size properties of beach sand, and measurement of short-term trends by use of fluorescent sand, and (7) examination of long-term shoreline change using old and recent maps.

The production of fluorescent sand tracer

Abstract A method for the production of fluorescent sand tracer developed in the Geography Department, University of Canterbury, is described. While the technique is broadly similar to that outlined by other workers, curing and crushing of labelled sand is carried out concurrently — rather than separately — thus streamlining the procedure.

AN OFFSHORE BEACH NOURISHMENT SCHEME

The University of Florida has conducted a series of tests to evaluate the effectiveness of beach nourishment from offshore sources by a specially designed drag scraper The field work, over a nine-month study period, included hydrographic surveys, fluorescent sand tracing, and a sand sampling program for two scraper sites at Jupiter Island, Florida The conclusions provide information as to the effect of the borrow pits and the dredged sand on the beach characteristics, the mechanisms of the filling of the pits, and the efficiency of the drag scraper.

Trend Surface Analysis of Sand Tracer Distributions on a Carbonate Beach, Bimini, B.W.I.

Two-dimensional trend surface analyses were performed on areally distributed tracer-concentration data for three different fluorescent sand tracers recovered from four depth intervals of the foreshore. The tracers had been affected by the swash, breakers, and longshore currents of one tidal cycle. Analysis of the statistical significance of trend surfaces for each depth interval showed that only the upper 2.5 cm. of the sand column evidenced definite trend components. Differential sorting of tracers of different shapes and mean grain sizes was probably negligible, as deduced from the similarity in direction of orthogonals to the trend surface contours for the various tracer data. The advantage of the trend surface method of describing sand movement patterns on beaches lies in its ability to represent, in an objective manner, the average movement of sand grains by means of a single representative equation. Furthermore, for time scales of the order of minutes to several hours, the motion of sand is seldom p...

FORMULATION AND USE OF FLUORESCENT TRACER COATINGS IN SEDIMENT TRANSPORT STUDIES

SUMMARYCommercially available, daylight and near‐ultraviolet fluorescent, colored dyes can be used in long‐ or short‐lived surface coatings on coarse sediments. Such tracer coatings make possible day‐ or nighttime visual and quantitative determination of river or beach sediment transport. Testing of five commercial coatings led to formulation of two additional coatings. A wide selection of dye colors is available for use in four coating mixtures. All coatings are insoluble in fresh or saline water. Single‐application coating thicknesses range between 0.0003 and 0.0024 inches. Still air drying time at room temperature for separated particles varies from 40 seconds to 14 minutes depending on coating mixture used. Volume production of marked particles in the field is possible.Extensive sediment sampling in particle transport studies possibly may be eliminated by measuring visible light emission from coated particles under nearultraviolet excitation. A battery operated, portable photometer was assembled from a light cell, linear amplifier, and metering circuit. Laboratory calibration indicates that 5% differences in areal concentration of marked particles at given sampling locations can be determined.Color coded sizes of fluorescent sand and gravel were used in a test of foreshore sediment transport pattern over a single tidal cycle. Initial trajectory (minimum transport angle) of particles moved by beach drifting is approximately equal to deep water angle of wave approach relative to the shoreline. Angular magnitude of the dispersion zone for each group of particles seems to be a function of particle size and point of introduction on the foreshore. Minimum average transport velocity of particles was 0.42 ft./min under test conditions.

Fluorescent Tracer Study of Eolian Sand Transport: ABSTRACT

Ten pounds of eolian sand were dyed fluorescent red and released on the crest of a large shadow dune at Windy Point, San Gorgonio Pass, California. The dune surface was sampled by pressing 3×3-in. Vaseline-coated cards onto the sands at predetermined stations downwind of the tracer point source. Westerly winds blew at 15-25 m.p.h. during the test. Sample cards were examined under ultraviolet light and the number of fluorescent grains per square inch determined for elapsed times of 3, 20 and 60 min. after tracer release. Isopleths of equal tracer concentration at the three elapsed times all delineated lobate patterns presumably in response to variable wind streamlines over the dune. At 2.5 hrs. after tracer release a lag deposit of very coarse fluorescent grains remained at the point source. The lag grains formed ripples with lengths three times those of the natural ripples. This suggests that ripple length is governed primarily by grain diameter and wind velocity. Analysis of tracer distribution revealed that fluorescent sand entered and left the sample grid at a constant rate. A decay curve of tracer loss from the point source indicated extinction of the point source occurred 157 min. after release. Difference between decay value and per cent of the total tracer on the dune at any moment was equivalent to per cent of tracer loss from the sample grid at any moment. Knowing the distance of grain movement, this relationship yielded an average tracer grain velocity of 30.36 in./min. Time-lapse motion pictures established that creep velocity, assumed to be equivalent to ripple velocity, was 0.153 in./min., indicating that grains in saltation were traveling roughly 198 times faster than grains in creep. This magnitude of difference between creep and saltation velocity is physically inconsistent with Bagnold's classic division of eolian sand load. End_of_Article - Last_Page 1762------------

The Use and Detection of Fluorescent Sand Tracers: ABSTRACT

Two recent developments, fluorescent tracers and a fluorescent particle counter, hold promise as practical means to the quantitative evaluation of littoral drift and sediment transport in rivers. Unlike radioactive material, luminophores present no health hazard or storage problems, offer a wider range of applicability, can be recovered in samples, and are more economical to use. The fluorescent tracers have been employed in studies of such specific problems of sediment migration as beach erosion, inlet stability, dune processes, and artificial beach nourishment. Fluorescent dyes and thermosetting plastics have been combined to coat sand in a process designed to produce the tracer material, so that the physical properties of tracers and the sediments are nearly identical. Of the several materials and techniques tested, urea-formaldehyde resin, fluorescing organic dyes, and a catalytic procedure imparted the best chemical and physical characteristics to the tracer grains. The application of tracers to sand transport studies became practical only with the invention of the fluorescent particle counter. This instrument provides a rapid and accurate method of frequency determination of tracer particles in sand samples, and therefore affords a much needed statistical treatment of sediment transport. The particle counter has been built on the principles of optics, electronics, and threshold decision logic, to differentiate simultaneously for four tracers, the fluorescent colors of which have been established through spectrophotometric measurements. Tracers in samples with concentrations varying from 10-7 to 10-2 are counted, tabulated, and recorded at the rate of 20,000 particles/second. End_of_Article - Last_Page 360------------