Effective Settling Velocity Research Articles

Settling velocity and effective density analysis for aquaculture floc particles: An approach through bivariate parametric copula

The study of flocs' characteristics in aquaculture tanks remains challenging due to their complex composition. Nevertheless, the application of experimental methods, such as particle tracking velocimetry (PTV), has made it possible to measure particle diameters and settling velocities. With the experimental data, bivariate distribution functions through copula modelling were employed to provide a more accurate estimation of the effective density of flocs through the empirical model proposed by Lau and Krishnappan. It was observed that the primary particle density constituting the flocs varied between 1051 kg/m³ and 1426 kg/m³. Moreover, when considering a variable primary particle density, effective floc density values ranging from 980 kg/m³ to 1500 kg/m³ were obtained for floc diameters ranging from 0.068 mm to 1.9 mm, respectively. This variation confirms that the b and c parameters of the Lau-Krishnappan model change for each floc diameter range following the quantiles associated with the conditional probability of diameter and settling velocity. Thus, employing copula approximation, a more accurate fit of the Lau-Krishnappan model was achieved, considering a wide range of particle diameters at the tails. This approach offers better estimates of floc effective density and settling velocity, essential for enhancing the selection and design of aquaculture tanks and settlers to ensure efficient solids removal.

Sedimentation in particle-laden flows with and without velocity shear

The vertical transport of sediment from particle-laden flows in marine settings can be enhanced by a settling-driven convective instability. The presence of a horizontal velocity shear can further influence this vertical transport. We conduct numerical simulations to investigate the vertical sediment transport in the presence and absence of shear. We show how this transport is determined by a competition between the growth of the settling-driven convective instability (Rayleigh–Taylor) and the stratified shear instability (Kelvin–Helmholtz). In the absence of shear, the Rayleigh–Taylor instability drives enhanced vertical sediment transport; this effect increases with the Stokes settling velocity of the particles and decreases with the stratification strength. In the presence of shear, there are two regimes of effective settling. When the Kelvin–Helmholtz instability grows rapidly and suppresses the Rayleigh–Taylor instability, the effective settling velocity is significantly reduced. On the other hand, if the Rayleigh–Taylor instability dominates and completely inhibits the Kelvin–Helmholtz instability, the effective settling velocity is enhanced due to the additional energy input by shear. We explore the parameter space of these regimes and interpret their physics.

Measurements of the sediment flocculation characteristics in the Three Gorges Reservoir, Yangtze River

AbstractThe flocculation of fine sediments in the Three Gorges Reservoir (TGR) was confirmed in previous studies, but the flocculation characteristics have yet to be fully clarified. In this study, field measurements were conducted in the TGR to investigate the sediment flocculation characteristics. First, the instantaneous flow velocity and sediment concentration were measured through Acoustic Doppler velocimeter and sediment sampling. Then, the effective settling velocity was calculated based on the sediment diffusion theory to deduce the floc size and flocculation degree. Finally, the influences of particle size, flow velocity, and sediment concentration on flocculation were analyzed. Results showed that flocculation occurred in more than half of the sediments in the TGR, and the maximum flocculation degree was between 10 and 30. Flocculation weakened as particle diameter increased, with the critical particle size being approximately 0.018 mm, meaning that flocculation was unlikely to occur when the particle size exceeded the critical value. As the flow velocity increased, the flocculation degree first increased and then decreased, with the critical flow velocity being approximately 0.7 m/s, but the critical flow velocity increased with an increase in sediment concentration and tended to be a constant. The flocculation degree also increased with increasing sediment concentration and tended to be constant when the sediment concentration exceeded approximately 0.5 kg/m3. The results provide new information on the flocculation characteristics of the TGR and should be useful for understanding and simulating fine sediment transport in the TGR.

Equivalence of turbulence statistics between monodisperse and polydisperse turbidity currents

Turbidity currents are buoyancy driven submarine flows where the source of buoyancy is typically a polydisperse sediment suspension. Sustained propagation of such flows depend on the ability of turbulence in the flow to keep the settling sediments in suspension. Recent studies by Cantero et al. (2012b) and Shringarpure et al. (2012) have investigated the interaction of monodisperse sediment suspension and turbulence in turbidity currents on smooth sloping beds. These studies showed that stable stratification of sediment suspension damps turbulence and in some cases can be fully suppress turbulence. Furthermore, it was shown that the turbulence damping effect of a monodisperse sediment suspension can be quantified by the product of shear Richardson number and the sediment settling velocity. In this study we generalize this result for a polydisperse sediment suspension. We compare the turbulence statistics of turbidity currents driven by different polydisperse suspensions and show that as long as the total amount of sediment and the product of shear Richardson number and effective settling velocity (a value representing the polydisperse suspension) are the same, the turbulent velocity statistics of the different polydisperse suspensions nearly collapse. Furthermore, if the effective settling velocity is chosen to be depth-dependent (a function of height from the bed) then the turbulence statistics involving sediment concentration also collapses between different polydisperse suspensions. These results suggest the possibility of modeling polydisperse currents with an equivalent monodisperse suspension whose total sediment load and depth-dependent settling velocity match those of the polydisperse suspension.

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

AbstractA 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, , and the overall effective settling velocity, , i.e., that velocity needed to predict the downward flux with . Results showed that was greater than the floc settling velocity in all runs. 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, , was found to be a strong function of the Richardson number, and conceptual and empirical equations are presented to predict as a function of the plume surface velocity, Ups, and Richardson number, Ri; this analysis showed that . In the runs with low Richardson number, 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.

Field measurements of settling velocities of fine sediments in Three Gorges Reservoir using ADV

The Three Gorges Reservoir (TGR) is suffering from unexpected fine sediment deposition, to better understand the fine sediment transport processes, field measurements were conducted at the Zhongxian and Fengjie reaches. A method based on the sediment diffusion equation was proposed to measure the settling velocities using the Acoustic Doppler Velocimeter (ADV). The backscatter acoustic intensities (BSI) received from the ADV were calibrated against the sediment concentrations measured via water sampling, suggesting a linear relationship in double logarithmic coordinate system. The instantaneous sediment concentration was calculated using the derived relationship, and then the settling velocity was obtained through the proposed procedure. The settling velocities of the fine particles in the TGR were found to vary with the water depth. Most of the effective settling velocities were within the range of 0.1–10mm/s, which were larger than those of the primary particles, indicating that the flocculation was likely to occur in the TGR. Additionally, it is suggested that the turbulent motion played an important role in the flocculation in the TGR.

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

AbstractWe 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.

Hindered Settling of Silt

AbstractSediment particles smaller than 64 μm, with a noncohesive base mineral, are referred to as silt. The settling velocity of suspended sediment decreases with increasing concentration due to hindered settling effects. Compared with clay and sand, hindered settling of silt is poorly documented and understood. A formulation is proposed for the hindered settling of silt-water mixtures, derived from physical reasoning. The effect of silt on the mixture’s viscosity is addressed in particular. The formulation compares favorably with laboratory experiments on the settling of silt-sized sediment. This study shows that effective settling velocities can be derived from a single concentration time series measured within the settling mixture, provided that the sediment is initially homogeneously distributed.

Analysis of Turbulence Suppression in Sediment-laden Saline Currents

The present work extends the results of Cantero et al.[1] and Shringarpure et al.[2] to the cases of sediment-laden saline currents. The flow is modeled as a channel flow where the forcing is exerted by salinity and suspended sediments. The resulting set of equations are solved by direct numerical simulation (DNS) for shear Reynolds number Reτ = 180. The DNS results show that by increasing the forcing due salinity, the flow can be held in a turbulent state whereby large sediment particles can be maintained in suspension. Typically, such large sediment particles would not be able to sustain the flow by themselves. The DNS results also show that for large sediment loads there is a transition to total turbulence suppression. This transition is abrupt and is caused by small changes in the sediment load. Here, salinity can be interpreted as a fraction of sediments that are fine enough that their settling velocity is negligible. Thus, the case of sediment-laden saline currents is physically equivalent to a simplified bi-disperse model where the fine sediments do not settle. Finally, this work shows that the original results by Cantero et al.[1] and Shringarpure et al.[2] hold when they are reinterpreted under the light on an effective settling velocity.

Sediment-laden fresh water above salt water: nonlinear simulations

AbstractWhen a layer of particle-laden fresh water is placed above clear, saline water, both double-diffusive and Rayleigh–Taylor instabilities may arise. The present investigation extends the linear stability analysis of Burns & Meiburg (J. Fluid Mech., vol. 691, 2012, pp. 279–314) into the nonlinear regime, by means of two- and three-dimensional direct numerical simulations (DNS). The initial instability growth in the DNS is seen to be consistent with the dominant modes predicted by the linear stability analysis. The subsequent vigorous growth of individual fingers gives rise to a secondary instability, and eventually to the formation of intense plumes that become detached from the interfacial region. The simulations show that the presence of particles with a Stokes settling velocity modifies the traditional double-diffusive fingering by creating an unstable ‘nose region’ in the horizontally averaged profiles, located between the upward-moving salinity and the downward-moving sediment interface. The effective thickness $l_{s}$ ($l_{c}$) of the salinity (sediment) interface grows diffusively, as does the height $H$ of the nose region. The ratio $H/l_{s}$ initially grows and then plateaus, at a value that is determined by the balance between the flux of sediment into the rose region from above, the double-diffusive/Rayleigh–Taylor flux out of the nose region below, and the rate of sediment accumulation within the nose region. For small values of $H/l_{s}\leqslant O(0.1)$, double-diffusive fingering dominates, while for larger values $H/l_{s}\geqslant O(0.1)$ the sediment and salinity interfaces become increasingly separated in space and the dominant instability mode becomes Rayleigh–Taylor like. A scaling analysis based on the results of a parametric study indicates that $H/l_{s}$ is a linear function of a single dimensionless grouping that can be interpreted as the ratio of inflow and outflow of sediment into the nose region. The simulation results furthermore indicate that double-diffusive and Rayleigh–Taylor instability mechanisms cause the effective settling velocity of the sediment to scale with the overall buoyancy velocity of the system, which can be orders of magnitude larger than the Stokes settling velocity. While the power spectra of double-diffusive and Rayleigh–Taylor-dominated flows are qualitatively similar, the difference between flows dominated by fingering and leaking is clearly seen when analysing the spectral phase shift. For leaking-dominated flows a phase-locking mechanism is observed, which intensifies with time. Hence, the leaking mode can be interpreted as a fingering mode which has become phase-locked due to large-scale overturning events in the nose region, as a result of a Rayleigh–Taylor instability.

Convective instability in sedimentation: 3-D numerical study

To provide a probable explanation on the field observed rapid sedimentation process near river mouths, we investigate the convective sedimentation in stably stratified saltwater using 3-D numerical simulations. Guided by the linear stability analysis, this study focuses on the nonlinear interactions of several mechanisms, which lead to various sediment finger patterns, and the effective settling velocity for sediment ranging from clay (single-particle settling velocity V0 = 0.0036 and 0.0144 mm/s, or particle diameter d = 2 and 4 μm) to silt (V0 = 0.36 mm/s, or d = 20 μm). For very fine sediment with V0 = 0.0036 mm/s, the convective instability is dominated by double diffusion, characterized by millimeter-scale fingers. Gravitational settling slightly increases the growth rate; however, it has notable effect on the downward development of vertical mixing shortly after the sediment interface migrates below the salt interface. For sediment with V0 = 0.0144 mm/s, Rayleigh-Taylor instabilities become dominant before double-diffusive modes grow sufficiently large. Centimeter-scale and highly asymmetric sediment fingers are obtained due to nonlinear interactions between different modes. For sediment with V0 = 0.36 mm/s, Rayleigh-Taylor mechanism dominates and the resulting centimeter-scale sediment fingers show a plume-like structure. The flow pattern is similar to that without ambient salt stratification. Rapid sedimentation with effective settling velocity on the order of 1 cm/s is likely driven by convective sedimentation for sediment with V0 greater than 0.1 mm/s at concentration greater than 10–20 g/L.

Determining the Existence of the Fine Sediment Flocculation in the Three Gorges Reservoir

Several proofs for the existence of flocculation in the Three Gorges Reservoir (TGR) are found through field measurements and laboratory experiments. The suspended particles and bed sediments are fine, and the particle diameters stay the same along the water depth, indicating that flocculation may occur. Both the vertical distributions of sediment concentrations (at low flow velocities) and measured settling velocities suggest that the effective settling velocities are larger than those of the primary particles, providing strong evidence for flocculation. The flow velocity zones of deposition and transportation are found, and the demarcation velocity of the two zones is approximately 0.5–0.6 m/s. It is thought that flocculation occurs when the flow velocity is smaller than the demarcation velocity; otherwise, the flocs will be disrupted by turbulent shear. Laboratory experiments are conducted by using the sampled bed sediments, and floc structures are also observed, confirming the existence of flocculation in the TGR.

Numerical simulation of turbulence and sediment transport of medium sand

A model of sand transport in water is produced by combining a turbulence-resolving large eddy simulation (LES) with a discrete element model (DEM) prescribing the motion of individual grains of medium sand. The momentum effect of each particle on the fluid is calculated at the LES cell containing the particle, and the fluid velocity and pressure, interpolated to each particle center, is used to derive fluid force on each particle in the DEM. Eleven numerical experiments are conducted of an initially flat bed of particles. The experiments span a range of motion, from essentially no motion to vigorous suspension. Hydraulic roughness is found to increase abruptly at the transition from bed load to suspended load transport. Suspended sediment extracts momentum from the flow and decreases the rate of shear. Whereas, slightly higher in the flow, vertical drag by suspended grains damps turbulence and increases the rate of shear. Vertical sediment diffusivity and effective particle settling velocity are much smaller than is commonly assumed in suspended sediment models. The bed load experiments suggest that saltation by itself is a poor model of bed load sand transport. In contrast to expectations from saltation models, the peak bed load flux occurs at essentially the same level as the bed, and grains move slowly in frequent contact with other grains. Higher- and faster-moving bed load grains that can be considered to be in saltation represent a smaller portion of the total flux. Entrainment of bed load grains occurs in response to fluid penetration of the bed by high-vorticity turbulence structures embedded within broader high speed fluid regions referred to as a sweeps or high-speed wedges.

Modelling potential effects of climate change on winter turbidity loading in the Ashokan Reservoir, NY

AbstractRecent studies have indicated that potential future climate change may lead to changes in the timing and quantity of snowpack accumulation and winter (November to April) streamflow patterns including increased streamflow and turbidity in early winter and a slight reduction in turbidity loads at the time of traditional early spring run‐off. In this study, we examine the potential effects of these predicted changes on reservoir turbidity levels. Our analysis focuses on Ashokan Reservoir, NY, which can at times receive significant watershed turbidity inputs mainly from stream channel erosion from the Esopus Creek. Both measured and simulated turbidity loads and climatology are input to CE‐QUAL‐W2 (W2), a reservoir turbidity transport model that can simulate reservoir turbidity and other water quality parameters. The W2 model is applied to estimate the effects of hydroclimatology on effective settling rates and turbidity transport as a result of differences in reservoir thermal structure during summer and winter events. Simulations suggest that the effective settling velocity is substantially lower at low temperatures during winter time. Winter average stream flow is simulated to increase by 12% and 20%, which leads to increases in reservoir turbidity by 11% and 17% for the future period 2046–2065 and 2081–2100, respectively. From a seasonal perspective, a change in timing of peak streamflow with increased flows during the winter and slightly reduced flows during early spring leads to increased average reservoir turbidity during winter and slightly decreased in‐reservoir turbidity during early spring and summer. Copyright © 2013 John Wiley & Sons, Ltd.

Assessment of the Treatment of Textile Mill Effluent Using UASB Reactor

This study was designed to evaluate the feasibility of the treatment of actual textile mill effluent using a upflow anaerobic sludge blanket (UASB) reactor. The main objective of this study was to generate design aids; in terms of organic loading rate (OLR), hydraulic retention time (HRT) versus chemical oxygen demand (COD) and colour removal in the textile effluent using a UASB reactor at neutral pH and constant mesophilic temperature. The COD, colour and total suspended solids concentration of the textile wastes used in the study were analyzed as 5440 mg/l, 3280 mg/l, 2320 units and 955 mg/l, respectively. The UASB reactor was started up by gradually increasing the OLR from 0.2 kg-COD/m3-day to 2.6 kg-COD/m3-day in order to prevent an organic shock to the reactor. Similarly, the hydraulic retention time (HRT) was slowly reduced from 58 h to 8 h to prevent the wash-out of sludge from the reactor. It was observed that more than 80% of COD and colour could be effectively removed at an OLR of 2.2 kg-m3/d and HRT of 20 h. At optimum operating conditions, the effluent volatile fatty acid concentration was observed to be 430 mg/l. The average biogas production observed during this study was 0.34 l/g-CODremoved and it was composed of 58% methane. During the course of maturity of granular sludge, its effective size and settling velocity were observed to increase exponentially as 0.261e0.051x and 1.91e0.017x respectively. The overall observed biomass yield (Yobs) for the experimental period was calculated as 0.049 g-VSS/g-CODrem. This study suggests that the use of a UASB reactor for textile mill effluent is a fairly feasible and viable option.

Fine particle deposition to porous beds

We summarize the results of flume experiments examining the transport behavior of dilute suspensions of silt‐sized particles carried in an open channel flow over three separate bed types including porous open mesh, glass beads, and small cobbles. In these experiments the time‐varying concentration of particles in suspension transport was measured as a function of suspended‐particle size and bed shear stress, and analyzed using a 1‐D model incorporating simultaneous deposition and entrainment. Rates of fine‐particle deposition to the bed are found to approach Stoke's settling velocity in slow flows, but diminish systematically with increasing bed shear stress and mean flow speed. No discernible re‐entrainment from the porous beds was observed, indicating that such beds act as an effective sink for fine particles. When our new results are compared to those of related, previously reported experiments examining fine‐particle transport over smooth impermeable beds, silt‐sized particles display similar behavior with regard to systematic reduction in deposition velocity independent of suspended‐silt‐particle size or bed porosity. This behavior is tentatively interpreted to reflect the effects of lift in a linear shear flow in excess of submerged weight of individual particles. Our findings compare favorably with values of effective settling velocity of fine particulate organic matter in natural channel flows reported elsewhere.

Particle boundary layer above and downstream of an area source: scaling, simulations, and pollen transport

AbstractDispersion of small particles emitted from an area source at the surface into a fully developed high-Reynolds-number boundary layer flow is studied as a theoretical model for pollen dispersion in the neutral atmospheric boundary layer. The particle plume above the area source is assumed to behave as a particle concentration boundary layer. Boundary layer scaling and the assumption of self-preservation lead to an analytical solution in the form of a similarity function that has an additional dependence on the ratio of gravitational settling and turbulent diffusion velocities. Similar arguments are used to predict patterns of deposition onto the surface downstream of the source. Theoretical predictions are tested using a suite of large-eddy-simulation numerical experiments, with good agreement. The combined analysis of theoretical and numerical results reveals interesting features in the patterns of downstream deposition, such as non-monotonic trends in isolation distance with particle settling velocity and surprisingly large isolation distances for practically relevant parameter ranges. Possible effects of turbulence on effective settling velocity are highlighted.

How does vegetation affect sedimentation on tidal marshes? Investigating particle capture and hydrodynamic controls on biologically mediated sedimentation

Plants are known to enhance sedimentation on intertidal marshes. It is unclear, however, if the dominant mechanism of enhanced sedimentation is direct organic sedimentation, particle capture by plant stems, or enhanced settling due to a reduction in turbulent kinetic energy within flows through the plant canopy. Here we combine several previously reported laboratory studies with an 18 year record of salt marsh macrophyte characteristics to quantify these mechanisms. In dense stands of Spartina alterniflora (with projected plant areas per unit volume of >10 m−1) and rapid flows (>0.4 m s−1), we find that the fraction of sedimentation from particle capture can instantaneously exceed 70%. In most marshes dominated by Spartina alterniflora, however, we find particle settling, rather than capture, will account for the majority of inorganic sedimentation. We examine a previously reported 2 mm yr−1 increase in accretion rate following a fertilization experiment in South Carolina. Prior studies at the site have ruled out organic sedimentation as the cause of this increased accretion. We apply our newly developed models of particle capture and effective settling velocity to the fertilized and control sites and find that virtually all (>99%) of the increase in accretion rates can be attributed to enhanced settling brought about by reduced turbulent kinetic energy in the fertilized canopy. Our newly developed models of biologically mediated sedimentation are broadly applicable and can be applied to marshes where data relating biomass to stem diameter and projected plant area are available.

Sediment eddy diffusivity and selective suspension under waves and currents on the inner shelf

Sediment diffusivity and effective settling velocity, we, (or equivalently grain size) of near-bed suspended sand was inferred from observed concentration profiles. Concentration data were obtained at 20-m depth off Dounreay, Scotland, and at 13-m depth off Duck, North Carolina, USA. These data accommodate different dynamic conditions (from wave-dominated at Dounreay to wind-driven current-dominated at Duck) and different sediment properties (median size of bed sediment ranging from 120 to 290 μm). Regression of observed concentration profiles using the Rouse-type diffusion equation yielded the Rouse parameter P=we/κu*, where κ is von Karman’s constant, u* is the characteristic shear velocity, and we is the effective settling velocity. Linearly increasing eddy diffusivity extended several times higher than the classical wave boundary layer and was not observed to strongly change slope at the top of the wave boundary layer. Instead, u* within several 10s of cm of the bed was nearly equal to wave-current shear velocity (u*cw) or current shear velocity (u*c) depending on whether conditions were wave- or current-dominated. For the Rouse parameter, it was found that u* ≈ u*c for u*c > ws and u* ≈ u*cw for u*c < ws, where ws is the median settling velocity of the bed sediment. The effective settling velocity in suspension (we) was, in turn, evaluated from P using independent estimates of u*cw and u*c. The inferred size of suspended sediment varied in response to forcing conditions. For an inverse Rouse number u*sf/ws near one, where u*sf is the skin-friction shear velocity, the representative grain size of suspended sediment approached the median size of bed sediment. A similar trend was seen for u*cw/ws or u*c/ws near two, depending on whether conditions were wave or current dominated. With increasing (or decreasing) u*/ws, the grain size of suspended sediment also increased (or decreased), suggesting selective suspension of sediment particles as a function of flow strength.

Influence of sediment settling velocity on mechanistic soil erosion modeling

We report on a series of soil erosion experiments performed on the 2‐m × 6‐m EPFL erosion flume. Total sediment concentrations and the concentrations of seven size fractions (&lt;2, 2–20, 20–50, 50–100, 100–315, 315–1000, and &gt;1000 μm) were measured during 14 high‐intensity (47.5–52.5 mm/h) rainfall experiments on three different slopes (2.2–12.4%). The short‐time and long‐time analytical solutions for the Hairsine‐Rose erosion model were rewritten to account for infiltration. The newly collected data were used to test the model under conditions that had not been explored before (steeper slopes, infiltration, more realistic soil composition). The analytical solutions could predict the observed total sediment concentration well. However, the observed sediment concentrations for the individual size classes could be predicted only when adjusted settling velocities were used. The adjusted settling velocities were estimated through manual optimization. The optimized settling velocities for the smallest and midsize particles (&lt;100 μm) were larger than calculated from Stokes' law or measured in a 0.47‐m tube, while the optimized settling velocities for the largest particles (&gt;315 μm) were smaller than measured. The effective settling velocities could also be calculated from the calculated amount of material in the shield of each size class at the end of the experiments. This calculated settling velocity distribution agreed very well with the optimized settling velocities. This study moves the Hairsine‐Rose model another step closer to an operational soil erosion model for field applications.