Settling Tube Analysis Research Articles

Field test comparison of an autocorrelation technique for determining grain size using a digital ‘beachball’ camera versus traditional methods

This extensive field test of an autocorrelation technique for determining grain size from digital images was conducted using a digital bed-sediment camera, or ‘beachball’ camera. Using 205 sediment samples and >1200 images from a variety of beaches on the west coast of the US, grain size ranging from sand to granules was measured from field samples using both the autocorrelation technique developed by Rubin [Rubin, D.M., 2004. A simple autocorrelation algorithm for determining grain size from digital images of sediment. Journal of Sedimentary Research, 74(1): 160–165.] and traditional methods (i.e. settling tube analysis, sieving, and point counts). To test the accuracy of the digital-image grain size algorithm, we compared results with manual point counts of an extensive image data set in the Santa Barbara littoral cell. Grain sizes calculated using the autocorrelation algorithm were highly correlated with the point counts of the same images ( r 2 = 0.93; n = 79) and had an error of only 1%. Comparisons of calculated grain sizes and grain sizes measured from grab samples demonstrated that the autocorrelation technique works well on high-energy dissipative beaches with well-sorted sediment such as in the Pacific Northwest ( r 2 ≥ 0.92; n = 115). On less dissipative, more poorly sorted beaches such as Ocean Beach in San Francisco, results were not as good ( r 2 ≥ 0.70; n = 67; within 3% accuracy). Because the algorithm works well compared with point counts of the same image, the poorer correlation with grab samples must be a result of actual spatial and vertical variability of sediment in the field; closer agreement between grain size in the images and grain size of grab samples can be achieved by increasing the sampling volume of the images (taking more images, distributed over a volume comparable to that of a grab sample). In all field tests the autocorrelation method was able to predict the mean and median grain size with ∼96% accuracy, which is more than adequate for the majority of sedimentological applications, especially considering that the autocorrelation technique is estimated to be at least 100 times faster than traditional methods.

Environmental response to a large, explosive rhyolite eruption: sedimentology of post-1.8 ka pumice-rich Taupo volcaniclastics in the Hawke's Bay region, New Zealand

The 1.8 ka eruption of the Taupo ignimbrite from the Taupo Volcanic Centre in the central North Island of New Zealand produced a ∼30 km 3 ignimbrite covering an area ca. 160 km in diameter, centred on Lake Taupo. Remobilisation of its pyroclastic detritus triggered major alluviation in the years to decades after its emplacement. In the Hawke's Bay region in the eastern North Island, three large rivers rise in the ignimbrite-impacted mountainous headwaters, in areas that were buried by up to 40 m of loose, unconsolidated pumiceous material. Analysis of preserved volcaniclastic sediments along valleys shows that resedimentation occurred in two main stages characterised by contrasting sediment:water ratios. The first comprised erosion and redeposition of ignimbrite debris by lahars, e.g. debris flows and hyperconcentrated flows. The second was marked by decreasing sediment:water ratios and the re-establishment of braided fluvial systems in the former river valleys, as recorded by such deposits as trough, planar, low-angle and antidune cross-bedded, planar-bedded, and ripple cross-laminated sands and gravels. However, there is no systematic chronological trend towards lower pumice contents in these fluvial facies. Four characteristic sets of co-occurring lithofacies were produced during the sedimentary response: (1) Laharic remobilisation association; (2) Upper-flow regime-dominated stream-flow association; (3) Lower-flow regime-dominated stream-flow association; and (4) Lacustrine association. Individual lithofacies were strongly controlled by the unusual hydrodynamic properties of pumice, particularly its low and variable density. Automated settling tube analysis of water-saturated pumiceous sediment confirms that sieve analysis is misleading with respect to the hydrodynamic behaviour of such sediments. Recasting granulometric data in terms of effective hydraulic grain size shows better sorting of mixed component sediments, but statistical sorting and mean grain-size parameters do not discriminate between the deposits of tractional and overcapacity parent flows. Therefore, particle behaviour is addressed by using both lithofacies and petrofacies in the description and classification of the remobilisation deposits.

Entrainment threshold of natural grains in liquids determined empirically from dimensionless settling velocities and other measures of grain size

Grain size plays a crucial role in sediment transport, but different methods of size analysis do not yield comparable results. Particle diameters obtained by settling tube, for example, cannot be employed in equations based on sieve sizes. Although the majority of experiments on the initiation of sediment motion has been based on sieve data, settling tube analysis is probably superior as both the settling rate and the entrainment threshold of grains are determined by the same factors of size, shape and density. In this paper, empirical equations are provided which allow the determination of a non-dimensional critical shear stress directly from the equivalent sedimentation diameter. The equations apply to the entrainment of well sorted grains with a high sphericity on flat sediment beds, and are valid for particles and liquids of different densities.

Comparison of flocculated and dispersed suspended sediment in the Dollard estuary

Abstract The purpose of this paper is to give a Lagrangian description of the changes in field settling diameter over a tidal period, while carrying out a tidal excursion with a research vessel. Settling tube analyses were carried out in the Dollard estuary, North-East Netherlands, by use of the Braystoke SK110 settling tube. From each tube settling velocity and grain size grading curves for the suspended material were computed. Subsequently, the sediment was dispersed from the filters and analysed in a laser diffraction analyser, a Malvern Mastersizer/E. The resulting grain size distribution of the primary particles was plotted together with the in situ distribution as bar diagrams. In this way it was possible to graphically determine the smallest equivalent floc size occurring in each sample as the intersect between the two distributions. Plotting this size against SSC, a linear relationship appeared: the greater the SSC, the smaller the smallest floc. It is suggested that this relates to high current velocities, at the same time causing both high values of SSC and high internal shear rates causing floc breakage. Plotting the settling velocities of the smallest floc against SSC yields an exponential relationship. Examples of the use of these relationships are presented. Flocs in the Dollard were larger than flocs sampled in the Danish Wadden Sea in earlier experiments. For comparative purposes, settling tube analyses were also carried out over the tidal flat.

An Excel program for computing the dynamic properties of particles in Newtonian fluids

Grain sizes of natural sediments can be determined by direct measurement of orthogonal axis dimensions, or alternatively by sieve or settling tube analysis. As these different techniques do not always give compatible results, published equations for modelling the hydrodynamic or aerodynamic behavior of particles have limited application. In this paper, an Excel program, which allows input from all three methods, is presented. The program calculates the settling velocity of spheres and ellipsoids as well as the critical shear stress at incipient grain motion in unidirectional fluid flow. Additional information includes the shape entropy of the particles, the drag coefficient, Reynolds numbers, and critical shear velocity. As the equations apply to particles of different densities in various liquids or gases, the program can be used for unusual situations such as modelling sediment entrainment on other planets.

Computer controlled settling tube analyses, calculations, and presentation of granulometric data

A batch of programs for rapid processing of sand and silt granulometric data has been in use at the Ben-Gurion University for several years. The data have been obtained from settling tube analyses. The batch begins with the digital output of the settling tube, converts the level of accumulation to percent accumulation and calculates a probability scale, and converts the time of settling into grain-size equivalents expressed in phi units; finally it gives the parameters of a modular triangle that represents the analyzed sample, showing: P = midpoints of grain sizes of the modal subpopulation, in phi units: S = relative sorting in absolute values; A = approach to lognormal distribution in percent. This process now is in use for both geological and engineering purposes.

Chi (X): A Proposed Standard Parameter for Settling Tube Analysis of Sediments

ABSTRACT The use of settling speed in the analysis of sedimentary particles has become sufficiently widespread to warrant standardization. This is necessary so that various researchers can communicate and compare results of their analyses. It is proposed that the standard parameter for settling speed be expressed in Chi () units: = -log2 (s/so) where s is the settling speed in meters per second (m/s) standardized to 20° C and so is standard speed of 1 m/s. Settling speed (s) can be temperature corrected to 20° C by the formula: s = sm + (k)*(20 - t)*sm The temperature correction factor k is given by the following: 1) For sm > 0.177 m/s: k = 0 (no correction necessary) 2) For Sm between 0.177 and 0.002 m/s: k = -0.00555*1n sm - 0.00961 3) For sm < 0.002 m/s: k = 0.025.

The Effects of Deposit Feeding Oligochaetes on Particle Size and Settling Velocity of Lake Erie Sediments

ABSTRACT Sediment collected from the western basin of Lake Erie has a median particle size of 1.5 µm and a median settling velocity of 0.0002 cm sec-1 measured by standard settling tube analysis. Microscopic examination of this sediment shows that most of the particles are bound into larger cylindrical aggregates by the feeding activities of tubificid oligochaetes (average pellet size = 280 µm length 70 µm diameter). Standard settling tube analyses destroy oligochaete fecal pellets and maintain particles in an unnatural disaggregated state. Laboratory experiments and field observations indicate that for most of the year the top 0.5-1 cm of western basin sediment is pelletized. Less destructive settling velocity m asurements of surface sediments yield median values of 1 cm sec-1 for tubificid fecal pellets, 0.06 cm sec-1 for the top 1 cm of western basin sediment, and 0.03 cm seca for degraded fecal pellets. No realistic measurement of the physical properties of Lake Erie sediments, of sediment erosion and transport, or of diffusion rates of pore water solutes can be made without understanding the biological processes active in fine grained sediments.

Size distribution of quartz in mudrocks

ABSTRACTSixteen penecontemporaneously deposited mudrock‐sandstone pairs ranging in age from Devonian to Cretaceous were treated chemically to isolate the quartz and chert fraction from the other constituents of the rocks. The amount of crystalline silica was determined from the chemical treatments; its size distribution was determined using a combination of normal and Micro Mesh sieving and settling tube analysis; the crystalline silica coarser than 10 μu was examined petrographically to determine the amount of chert.Percentages of crystalline silica in the mudrocks range from 6·7 to 46·7 % and average 27·6 (σ= 10·7). Mean grain size ranges from 4·4 φ to 7·3 φ and averages 6·1 φ. The crystalline silica fraction is a poorly sorted medium to fine silt consisting of one‐eighth sand, six‐eighths silt, and one‐eighth clay size sediment. Percentage of crystalline silica and mean size of crystalline silica in the thirty‐two mudrocks and sandstones are positively correlated; r= 0·685, which is significant at the 99 % level. The best fit linear regression line is: Y= 102·7–11·3X.Extrapolation of the regression line indicates that, on the average, crystalline silica is lacking in mudrocks in grain sizes finer than 9·1 φ (1·μm), a result consistent with observations by clay mineralogists.The crystalline silica fraction of both the mudrocks and associated sandstones averages 4% chert in the &gt;10 μm portion. There is no correlation between the mean grain size of the crystalline silica and the percentage of chert in it.

Field method for sieve analysis of sand

A field method for the mechanical analysis of sand is attained by using a sieve and cylinder combination. The sand is passed through a nest of sieves, and the fraction remaining on each is measured in a graduate cylinder. This method is simple and rapid, and the results obtained are comparable with the settling tube analyses.