Kyle Strom

A fully-automated image processing technique to improve measurement of suspended particles and flocs by removing out-of-focus objects

A fully-automated image processing script was developed to analyze large datasets of imaged flocs in dilute turbulent suspensions of mud. In the procedure, out-of-focus flocs are automatically removed from the dataset to attain a more precise floc size distribution. This automated technique was tested against visual inspection of images to ensure that the procedure was only selecting in-focus flocs for inclusion in the size measurements, and the resulting measured sizes were compared to floc measured through manual image processing of the same data. The results show that the automated method is able to accurately measure the floc size distribution by correctly sizing in-focus flocs and removing out-of-focus flocs. The processing procedures were developed with sizing of suspended mud flocs in mind, but the process is general and can be applied for other applications. We show the ability of the method to handle large numbers of images (over 15,000 at a time) by tracking the change in floc size population with time at 1-min intervals over the course of a 160min floc growth experiment.

Comparison of automated image-based grain sizing to standard pebble-count methods.

This study explores the use of an automated image-based method for characterizing grain-size distributions (GSDs) of exposed open-framework gravels by comparing the GSDs measured with the image-based method to distributions obtained with two pebble-count methods. Selection of grains for the two pebble-count methods was carried out using a gridded sampling frame and the heel-to-toe Wolman walk method at six field sites. At each site, 500-particle pebble-count samples were collected with each of the two pebble-count methods and digital images were systematically collected over the same sampling area. For the methods used, pebble counts collected with the gridded sampling frame were assumed to be the most accurate representations of the true grain-size population. Therefore, results from the image-based method were compared to the grid-derived GSDs for accuracy estimates; comparisons between the grid and Wolman walk methods were conducted to give an indication of possible variation between commonly used methods for the particular field sites used in the study. The grain-size comparisons were made at two spatial scales. At the larger scale, results from the image-based method were integrated over the sampling area required to collect the 500-particle pebble-count samples. At the smaller sampling scale, the image derived GSDs were compared to those from 100-particle, pebble-count samples obtained with the gridded sampling frame. The comparison shows that the image-based method performed reasonably well on five of the six study sites. For those five sites, the image-based method slightly underestimated all grain-size percentiles relative to the pebble counts collected with the gridded sampling frame, but the method performed well in estimating the median grain size (the average bias for ψ 5 , ψ 50 , and ψ 95 was 0.07ψ, 0.04ψ, and 0.19ψ, respectively). The Wolman pebble-counts yielded coarser results than the pebble counts obtained with the gridded sampling frame, especially for the smaller percentiles (the average bias for ψ 5 , ψ 50 , and ψ 95 was 0.20ψ, 0.16ψ, and 0.04ψ, respectively). Oversegmentation of large pitted grains in the image-analysis procedures was identified as a leading cause for failure of the image-based method at one of the sites. It is likely that lower degrees of oversegmentation and physical particle orientation contributed to the slight underestimation of all grain-size percentiles in the image-based method.

Hydraulic and sediment transport properties of autogenic avulsion cycles on submarine fans with supercritical distributaries

Submarine fans, like other distributive systems, are built by repeated avulsion cycles. However, relative to deltas and alluvial fans, much less is known about avulsions in subaqueous settings. In this study, we ran a set of subaqueous fan experiments to investigate the mechanics associated with autogenic avulsion cycles of self-formed channels and lobe deposits on steep slopes. The experiments used saline density currents with crushed plastic to emulate sustained turbidity currents and bed load transport. We collected detailed hydraulic and bathymetric measurements and made use of a 1-D laterally expanding density current model to better understand different aspects of the avulsion cycle. Our results reveal three major components of the avulsion cycles: (1) distributary channel incision, extension, and stagnation; (2) mouth bar aggradation and hydraulic jump initiation; and (3) hydraulic jump sedimentation and upstream retreat. Interestingly, in all but one experiment, the avulsion cycles led to fans that remained perched above the basin slope break. Experimental data and hydraulic theory were used to unravel actual mechanics associated with cycles. We found that channels stopped extending into the basin due to a decay in sediment transport capacity relative to sediment supply and that the reduction in capacity was primarily an outcome of expansion-driven velocity reduction; dilution played a secondary role. Once channel extension ceased, mouth bar deposits aggraded to a thickness approximately equal to the critical step height needed to create a choked flow condition. The choke then initiated a hydraulic jump on the upstream side of the bar. Once formed, the jump detained a majority of the incoming sediment and forced the channel-to-lobe transition upstream, filling the channel with steep backset bedding and capping the entire channel with a mounded lobate deposit. These intrinsic processes repeated through multiple avulsion cycles to build the fan.

Bedload Predictions by Using the Concept of Particle Velocity: Applications

Measurement of sediment transport is necessary to determine the amount of sediment load and to establish or check analytical or empirical sediment transport equations. These measurements differ in principle according to the mode of sediment transportation, i.e., bed load and suspended load, and the type of the transported sediment, i.e., clay, sand, and gravel. The focus of the proposed investigation is found on bed load transport (i.e., rolling, sliding, or bouncing) of gravel particles. Bed load is difficult to measure for several reasons. Any mechanical device placed in the vicinity of the bed will disturb the flow and hence the rate of bed-load movement. Moreover, it is very difficult to develop a device that accurately collects all the size fractions of the bed load. Finally, it is difficult to measure bed load rates in the field due to lack of access in some areas, especially at high flows, and lack of reliable measuring devices. The objective of this research is to employ an image analysis technique to monitor bedload motion in a laboratory flume under different flow and bed roughness conditions; and obtain unique information about the velocity of individual particles.

Sedimentation from flocculated suspensions in the presence of settling‐driven gravitational interface instabilities

We experimentally examine sedimentation from a freshwater suspension of clay flocs overlying saltwater in the presence of gravitational instabilities. The study seeks to determine: (1) if flocculation hampers or alters interface instability formation; (2) how the removal rates of sediment from the buoyant layer compare to those predicted by individual floc settling; and (3) whether or not it is possible to develop a model for effective settling velocity. The experiments were conducted in a tank at isothermal conditions. All experiments were initially stably stratified but later developed instabilities near the interface that grew into downward convecting plumes of fluid and sediment. Throughout, we measured sediment concentration in the upper and lower layers, floc size, and plume descent rates. The data showed that flocculation modifies the mixture settling velocity, and therefore shifts the mode of interface instability from double-diffusive (what one would expect from unflocculated clay) to settling-driven leaking and Rayleigh-Taylor instability formation. Removal rates of sediment from the upper layer in the presence of these instabilities were on the same order of magnitude as those predicted by individual floc settling. However, removal rates were found to better correlate with the speed of the interface plumes. A simple force-balance model was found to be capable of reasonably describing plume velocity based on concentration in the buoyant layer. This relation, coupled with a critical Grashof number and geometry relations, allowed us to develop a model for the effective settling velocity of the mixture based solely on integral values of the upper layer.

Bed Load Measurements and Testing of the Gravel Transport Sensor (GTS)

There are several limitations to the current methods of measuring bed load in gravel bed stream. To combat these limitations a new devise, the Gravel Transport Sensor (GTS), has been developed by D & A Instruments. Preliminary testing on a GTS prototype was conducted to examine the instruments ability to detect different size particles over a range of flow conditions. Preliminary results showed the ability of the GTS to detect particles moving as bed load reduces with a reduction in particle size.

Sedimentation from buoyant muddy plumes in the presence of interface mixing: An experimental study

A series of flume experiments were conducted to study the sediment removal rates, characterized by an effective settling velocity, from buoyant muddy plumes overriding clear saltwater at steady state conditions under different Richardson numbers and initial suspended sediment concentrations. The experiments were all carried out in the subcritical regime, leading to cusps style instabilities at the interface of the two fluids. Flocculation in the experiments was not suppressed, yet flocs remained small while in the plume layer. Data from the experiments allowed for calculation of the individual floc settling velocity, Ws,f, and the overall effective settling velocity, Ws,eff, i.e., that velocity needed to predict the downward flux with CWs,eff. Results showed that Ws,eff was greater than the floc settling velocity in all runs. Ws,eff was found to increase with plume velocity and interface mixing but not with plume concentration. The difference between the effective and floc settling velocities, was therefore attributed to turbulent diffusion brought on by mixing at the interface and not to convective sedimentation or leaking. The turbulence enhanced settling velocity, Ws,t, was found to be a strong function of the Richardson number, and conceptual and empirical equations are presented to predict Ws,t as a function of the plume surface velocity, Ups, and Richardson number, Ri; this analysis showed that Ws,t ∝UpsRi−2. In the runs with low Richardson number, Ws,t was approximately equal to the floc settling velocity, leading to an overall doubling of the effective settling velocity relative to that of the individual particles. This article is protected by copyright. All rights reserved.

Relationship between Acoustic Backscatter Strength and Suspended Sediment Concentration using a 6 MHz Nortek Vector Velocimeter

1 ABSTRACT This paper presents a laboratory study that evaluates the relationship between suspended sediment concentration (SSC) and the acoustic backscatter strength recorded by a Nortek Vector velocimeter for dierent natural and commercial sediments. Tests were conducted in a tank using kaolinite and three other types of natural mud taken from the Houston Ship Channel. SSCs ranged from 0.001 to 7 g/l for kaolinite and 3.5 g/l for natural sediments. Results show two regions of response in the relationship between the acoustic return and the SSC. The first region was for concentrations less than 3.2 g/l. In this region, the strength of the return signal is linearly related to the logarithm of concentration with a constant positive slope. Above this concentration, the strength of the acoustic return decreases with increased concentration. The study examines the dierence in these basic trends among the dierent sediment types.

Monitoring Small Scale Developments in Bedforms and Bedload Transport

The paper presented here examines the utilization of a digital camera in monitoring the evolution of cluster microforms in a laboratory flume. Two types of experiments were conducted to examine the spacing of self organized cluster microforms and their effects on bedload transport. The use of the digital video camera in concurrence with other analysis tools allowed for the examination of cluster spacing under varying flow conditions, accurate continuous bedload sampling (bedload samples at less than 1/sec), and the examination of integration and disintegration of particles into and out of individual clusters. Utilization of the digital camera proved useful and accurate in the lab setting. Introduction Small-scale cluster bedforms, or microforms, are prevalent features in gravel-bed rivers. An understanding of the mechanics associated with them is needed for a more comprehensive understanding of river processes, as well as the development of accurate predictive tools for bed roughness characteristics, stage-discharge relations, bedload transport, and implementation of restoration plans. Bedform structures are one component of the nonlinear system of gravel-bed rivers (Kuhnle 1996, Muller and Gyr 1996, Gomez and Phillips 1999, Lanzoni and Tubino 1999). Bedforms are produced by flow structure and entrainable sediment; once developed, they in turn influence sediment transport and the surrounding flow field. The complexity of these interactions and the inability to account for them has lead to site specific resistance and bedload formulas, which produce predictions with large errors and degrees of variability (Brayshaw 1984, Gomez and Church 1989, Rickenmann 2001). One hindrance in the study of microtopography and bedload transport is the fact that bed evolution occurs during high flow events, making it difficult to make real-time measurements of bedload and observations during the formation and disintegration process. Most field studies conducted on evolution of clusters have been limited to observations of tagged particles before a runoff event and then again after normal flow conditions have returned (Billi 1988, de Jong 1991, Mikos and Escorza 2000). The purpose of this paper is to examine the use and analysis of digital video in monitoring cluster microform development and bedload transport. Background information and further analysis and results of the fundamental aspects of the study on cluster development and effects on bedload transport can be found in Strom et al. (2002). However, a short description of the test setup will be presented here to better help the read understand the conditions of the tests and analysis of the digital video. Copyright ASCE 2004 HMEM 2002 Setup The experimental runs were conducted in a flume at the Albrook Hydraulic Laboratory of Washington State University. The flume is a 22 m long, 0.9 m wide, water recirculating flume capable of attaining slopes of up to 13% by means of motor-driven screw jacks. Figure 1 is a schematic of the flume and experimental set up. The test section, which is 4.2 m in length, was located 17m downstream of the headbox to ensure that fully developed flow conditions were present during the experiments. The digital video camera was mounted on a rolling trolley located above the test section (Fig. 1). Two types of experiments where carried out, one for monitoring the development and spacing of cluster microforms under varying flow conditions and the second for determining the effects that clusters had on bedload transport. For the first type of experiments, i.e. cluster development and spacing, pre-set marks for trolley position were used so that the camera position could be quickly changed to ensure that the whole test section was captured and that camera positions were constant from placement to placement. To monitor bedload transport, the trolley was placed in one location for the duration of the test so as to capture some of the clusters located in the downstream end of the test section as well as the exit of particles out of the test section. Green spherical glass particles of 8mm diameter were used as active layer sediment for the development of clusters. This was done atop a uniform roughness bed comprised of clear 8mm spherical particles packed as tightly as possible (Fig. 2, shows active layer sediment, green clusters, atop uniform roughness bed of clear particles). Figure 1. Flume and digital video camera setup Cluster Spacing Analysis One objective of the test was to determine if clusters formed with any kind of pattern regularity with respect to each other. That is, do clusters have, in general, a predictable spacing in relation to each other for varying flow conditions. To quantify cluster spacing at each of the bed shear stress conditions that clusters where found to form under (Table 1), the following procedures Copyright ASCE 2004 HMEM 2002 where followed. First, still images of the bed for each flow condition where captured from the digital video with the program PhotoDV. The pictures where then opened in Adobe Photoshop for quantification of cluster spacing. Test τ* S h Q Ubulk Re Fr u* Rep B/h (%) (m) (m/s) (m/s) (m/s) (m/m) 1.25τ*cr 0.01 0.2 0.063 0.0233 0.416 2.78E+04 0.53 0.035 247 14.1 1.5τ*cr 0.012 0.2 0.076 0.0335 0.5 3.91E+04 0.57 0.039 271 11.7 1.75τ*cr 0.014 0.2 0.089 0.0417 0.526 4.76E+04 0.56 0.042 294 10.0 2.0τ*cr 0.016 0.2 0.103 0.0518 0.565 0.00E+00 0.56 0.045 316 8.6 Table 1. Flow conditions for which cluster where found to form Cluster spacing in relation to each other was described by longitudinal spacing λx, transverse spacing λy, and an angle of orientation αc (Fig. 2). For consistency, this spacing was defined from the stoss tip of one cluster to that of the next (where the “stoss” is the front of a cluster). The overall shape and alignment of clusters was similar to other reports (Brayshaw 1984, de Jong 1991, Hassan and Reid 1990) in that they aligned and elongated in the flow direction, and have an offset diagonal spacing (Fig. 2).