ERDC/CHL TR-20-8 

Sediment Sorting by Hopper Dredging and 

Pump-Out Operations

Conceptual Model and Literature Review 

Coastal and Hydraulics Laboratory 

Anthony M. Priestas, S. Jarrell Smith, and Katherine E. Brutsché May 2020

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 ERDC/CHL TR-20-8 

May 2020 

Sediment Sorting by Hopper Dredging and 

Pump-Out Operations

Conceptual Model and Literature Review

Anthony M. Priestas, S. Jarrell Smith, and Katherine E. Brutsché

Coastal and Hydraulics Laboratory

US Army Engineer Research and Development Center

3909 Halls Ferry Road

Vicksburg, MS 39180-6199

Report 1 of 2

Approved for public release; distribution is unlimited. 

Prepared for Regional Sediment Management Program 

3909 Halls Ferry Road 

Vicksburg, MS 39180-6199

Under Funding Account Code D86F00; AMSCO Code 008303
ERDC/CHL TR-20-8 ii

Abstract

Dredged sediment placed on beaches or nearshore environments is

customarily evaluated for compatibility with the native beach sediment to 

avoid unintended impacts to economic, environmental, or recreational 

resources. Consequently, some state regulatory authorities establish limits 

upon the fine-grained content for sediment designated for placement on 

certain beaches and nearshore environments. Hopper dredging operations 

for beach and nearshore placement typically include periods of overflow, 

which is recognized to produce some degree of separation between the size 

fractions of the dredged sediment. The degree of separation and the 

controlling factors of separation are presently poorly known and are the 

subject of this research. This report provides a conceptual model of the 

hopper dredging and placement processes, including the relevant 

processes associated with hopper dredge-associated sediment dynamics, 

generation and transport of the overflow sediment plume, and sediment 

winnowing at the beach outflow. Prior research is described, and 

knowledge gaps are identified. Finally, a research plan to validate prior 

research and to address knowledge gaps is presented. An annotated 

bibliography of relevant literature is given in an appendix. Documentation 

of the planned research presented herein will appear in future publications 

associated with this study.

DISCLAIMER: The contents of this report are not to be used for advertising, publication, or promotional purposes. 

Citation of trade names does not constitute an official endorsement or approval of the use of such commercial products. 

All product names and trademarks cited are the property of their respective owners. The findings of this report are not to 

be construed as an official Department of the Army position unless so designated by other authorized documents.

DESTROY THIS REPORT WHEN NO LONGER NEEDED. DO NOT RETURN IT TO THE ORIGINATOR.
ERDC/CHL TR-20-8 iii

Contents

Abstract.................................................................................................................................... ii

Figures......................................................................................................................................iv

Preface......................................................................................................................................v

1 Introduction ...................................................................................................................... 1

1.1 Background........................................................................................................1

1.2 Objective ............................................................................................................2

1.3 Approach ............................................................................................................3

2 Conceptual Model............................................................................................................ 4

2.1 Separation of sediment by hopper dredging ...................................................9

2.1.1 Tank sedimentation .................................................................................................... 9

2.1.2 Models of tank sedimentation and separation .......................................................10

2.2 Separation of sediment by pipeline outfall and beach processes ...............15

2.2.1 Pipeline outfall...........................................................................................................16

2.2.2 Separation of sediment due to nearshore and beach processes ..........................17

2.3 Transport processes in TSHD overflow plumes ............................................ 18

2.3.1 Dynamic plume .........................................................................................................19

2.3.2 Passive plume ...........................................................................................................19

2.3.3 Modeling of the overflow plume...............................................................................20

2.4 Sampling methods.......................................................................................... 22

2.4.1 Bed material sampling..............................................................................................23

2.4.2 Overflow weir sampling.............................................................................................24

2.5 Uncertainty in quantifying losses................................................................... 26

3 Conclusions and Recommendations...........................................................................27

3.1 Conclusions ......................................................................................................27

3.2 Proposed research ......................................................................................... 28

3.3 Conceptual model and literature review....................................................... 28

3.4 Sampling methods.......................................................................................... 28

3.5 Field measurements of sediment sorting during dredging 

operations................................................................................................................. 29

References.............................................................................................................................30

Appendix: Annotated Bibliography of Relevant References by Topic ............................35

Unit Conversion Factors.......................................................................................................44

Acronyms and Abbreviations...............................................................................................45

Report Documentation Page
ERDC/CHL TR-20-8 iv

Figures 

Figures 

Figure 1. Schematization of the dredging cycle and sampling points during the 

loading stage (A) and discharge stage (B). A mass balance approach is used to 

determine the loss of fine material between the borrow area (B) and placement 

area along a beach (BCH). The mass balance approach tracks flow Q and 

sediment concentration (C) at the inflow (I), overflow OV, and pump out (P). 

See text for additional details.................................................................................................... 5

Figure 2. Mass balance of sediments during a dredging cycle. ............................................ 7

Figure 3. Conceptual model of an ideal settling tank. In this model, D is the basin 

depth, and L is the basin length. Sediment enters the basin from the inlet zone 

with a uniform vertical concentration and horizontal velocity VH. Particles then 

settle with velocity Vs according to Stokes Law. A particle is considered lost to

overflow only if the vector sum of VH and Vs is greater than the basin length (i.e., 

the settling time is less than the time to travel the distance L). Adapted from 

Camp (1936).............................................................................................................................11

Figure 4. Schematization of flow for a single inlet settling tank based on the 

observations of van Rhee (2001). Figure adapted from van Rhee (2002)........................13

Figure 5. Cumulative overflow losses as a function of the dimensionless hopper 

load parameter based on sand fluxes. Adapted from van Rhee (2001). ...........................14

Figure 6. Photo of the custom flow-through sampler used by Kerssermaker 

(2004). Image on the right shows the sampler deployed on the bell mouth of an 

overflow weir. Figure adapted from HR Wallingford (2003). ................................................25
ERDC/CHL TR-20-8 v 

Preface 

This study was conducted for the Regional Sediment Management 

Program through an Interagency Agreement (IAA, number M16PG00023) 

between the US Department of the Interior, Bureau of Ocean Energy 

Management (BOEM); the US Army Corps of Engineers (USACE), 

Jacksonville District (SAJ); and the US Army Engineer Research and 

Development Center (ERDC), Coastal and Hydraulics Laboratory (CHL),

Regional Sediment Management (RSM) Program, under Funding Account 

Code D86F00; AMSCO Code 008303. Funding was provided by BOEM 

and the USACE ERDC RSM Program. 

Dr. Clay McCoy was the Technical Lead and Project Manager from SAJ, 

Mr. Doug Piatkowski was the Contracting Officer’s Representative for 

BOEM, and Ms. Leighann Brandt was the Technical Lead from BOEM. 

Support for the development and implementation of the IAA was provided 

by Ms. Jackie Keiser, Mr. Jason Engle, and Dr. Kelly Legault of the RSM 

Regional Center of Expertise. The USACE administrative point of contact 

was Ms. Liz Fiocchi. Mr. Douglas Piatowski, Ms. Leighann Brandt, and 

Mr. Paul Knorr (BOEM), Dr. Michael Miner (The Water Institute of the 

Gulf), and Dr. Clay McCoy (SAJ, RSM Regional Center of Expertise) are 

thanked for the development of the study concept and their valuable input 

toward the study plan and methods. 

The work was performed by the CHL Field Data Collection and Analysis

Branch and the Coastal Engineering Branch of the Navigation Division, 

ERDC, CHL. At the time of publication of this technical report, 

Mr. William C. Butler was Chief of the Field Data Collection and Analysis 

Branch, and Ms. Lauren M. Dunkin was Chief of the Coastal Engineering 

Branch. Dr. Jacqueline S. Pettway was Chief of the Navigation Division. 

Dr. Katherine E. Brutsché was the USACE National RSM Program 

Manager, and Mr. Charles E. Wiggins was the ERDC Technical Director 

for Navigation. The Deputy Director of CHL was Mr. Jeffrey R. Eckstein, 

and Dr. Ty V. Wamsley was the Director. 

COL Teresa A. Schlosser was the Commander of ERDC, and the Director 

of ERDC was Dr. David W. Pittman. 
ERDC/CHL TR-20-8 1 

1 Introduction 

This report is part of a broader effort to determine the separation (Phase I) 

and fate (Phase II) of fine sediments discharged through hopper dredging 

and pump-out operations. Phase I consists of three research components: 

(1) background review, (2) laboratory experiments, and (3) field sampling 

and analysis. As part of the Phase I research, this (first) report 

conceptually evaluates the degree of sediment separation from trailing

suction hopper dredges (TSHD) and pump-out operations, and presents a 

background review of the relevant literature. A subsequent (second) report 

from Phase I will present the findings from laboratory tests and numerical 

experiments aimed at determining appropriate sediment collection and 

analysis methods. The final (third) report from Phase I will present the 

findings of the field campaign whereby the loss rate of fine sediment is 

quantified at various stages of the dredging process. The final report will 

be published through the Bureau of Ocean Energy Management (OCS 

Study BOEM 2019-010). 

1.1 Background 

In shore protection, ecosystem restoration, and navigation projects where 

sediment is placed on the beach or in the nearshore, coastal project 

managers are required to ensure that sediment taken from source areas 

(e.g., offshore borrow site, navigation channel, inlet complex) is 

compatible with the sediment characteristics at the placement site (e.g., 

the beach or nearshore). Important factors to consider are sediment grain 

size, composition, sorting, and color. Additionally, some state regulations 

across the nation specify allowable thresholds of percent abundance of fine 

sediment relative to sand content. The threshold size for fine sediment is 

defined as either the sediment passing the #200 (0.075 mm)1 sieve, in 

accordance with the Unified Soil Classification System, or the material 

passing the #200 (0.063 mm) sieve in accordance with the UddenWentworth scale. 

 

1 For a full list of the spelled-out forms of the units of measure used in this document, please refer to US 

Government Publishing Office Style Manual, 31st ed. (Washington, DC: US Government Publishing 

Office 2016), 248-52, https://www.govinfo.gov/content/pkg/GPO-STYLEMANUAL-2016/pdf/GPOSTYLEMANUAL-2016.pdf. 
ERDC/CHL TR-20-8 2 

When determining compatibility between the source sediment and the 

native sediment, it is typically assumed that textural properties (e.g., 

sorting, mean grain size, and percent sand) are maintained from the 

in situ borrow area, through dredging and conveyance, to the placement 

site. However, it is generally recognized that hopper dredges 

implementing overflow (the intentional discharge of supernatant water)

coarsen their load respective to the source material through preferential 

loss of fines suspended in overflow (the gain in hopper load through this 

process is known as economic loading). Generally, the present methods for 

assessing sediment compatibility do not adequately reflect the changes in 

grain size characteristics between the borrow area and what is 

subsequently placed on the beach. 

Understanding and quantifying the coarsening of sediment in the hopper 

load would allow coastal managers to better estimate the size 

characteristics of the material at the placement location compared to the 

source material. It is hypothesized that, based on this coarsening process 

during dredging operations, use of source material containing a higher 

concentration of fines could be used in coastal flood risk management, 

ecosystem restoration, and navigation projects, leading to potential cost 

savings while expanding potential source volumes. 

1.2 Objective 

The objective of this study is to quantify changes in sediment 

characteristics (i.e., grain size, sorting) and the degree, timing, and 

variability of sediment sorting during dredging, pump out, and placement 

operations. This information is presented so that the results and methods 

can be applied to inform sediment compatibility analyses and subsequent 

management of offshore sediment resources. The degree of sediment 

separation by size class will be quantified throughout the dredging process 

including (1) at the in situ borrow site as a baseline for comparison, (2) 

during overflow with particular emphasis on the proportion of fines lost, 

and (3) during pump out at the beach. As discussed in detail in Chapter 3, 

several tasks have been outlined to meet the objectives of this study, 

including this report, a lab experiment to test and refine sampling 

methodologies, and the employment of those methodologies in the field to 

quantify fines loss from in situ source material to placement location.
ERDC/CHL TR-20-8 3 

1.3 Approach

Chapter 2 of this report presents the conceptual model beginning with an 

overview of the dredging process from source to placement area, and 

identifies points of sediment sorting and loss of fines during that process.

Generally, loss occurs in the hopper during overflow, as well as at the 

pipeline outflow at the placement site. Once placed on the beach or the 

nearshore, sediments are further winnowed by natural coastal processes 

(i.e., waves and currents). Chapter 2 also includes a discussion on the 

transport processes of the fine sediment in the plume associated with 

overflow and potential sampling methods for the study. A brief discussion 

of uncertainty in quantifying losses is also included. Chapter 3 discusses 

the proposed research including both laboratory and field experiment 

methods. An appendix is included containing an annotated bibliography of 

the relevant references by topic. 


ERDC/CHL TR-20-8 6 

sediments, which are then carried offshore, in addition to winnowing by 

subsequent waves and tides. The goal of the present research is to quantify 

these losses at each point in this process using a mass balance approach 

(Figure 2). For this approach, the following assumptions are made:

• Negligible loss of fines at the drag head. 

• Negligible effect or likelihood that overflow sediments are reintroduced 

at the drag head. 

• Negligible loss of fines associated with pipeline transport. 

• All sediments are fully retained within the hopper during the loading 

stage (excepting during overflow) and fully removed during the 

discharge stage. 

At the site of the drag head, some sediment resuspension may occur as the 

drag head is often equipped with jets or teeth to loosen the sediment prior 

to being suctioned to improve production efficiency, which may mobilize 

fine sediment to the water column. This process may be exacerbated if the 

forward speed of the dredger is too fast (i.e., not optimized relative to 

suction capacity). In general, however, these are thought to not contribute 

significantly to the loss of fines because the pressure difference over the 

drag head causes high flow potentials close to the drag head (Vlasblom 

2007), which is speculated to minimize resuspension. Instead, based on 

previous experience, there exists the possibility that some finer material 

from the overflow plume (discharged from the hopper) may settle and be 

re-entrained into the suction line, which would enrich the inflow with fine 

sediment (though the extent to which this condition occurs is unknown 

and likely dependent of site-specific conditions). Additional losses may 

occur through leakage of the hopper doors or hull and through pipeline 

connections; however, all these losses are considered negligible from a 

mass balance perspective and are not considered in this analysis. 







ERDC/CHL TR-20-8 14

Figure 5. Cumulative overflow losses as a function of the dimensionless hopper load 

parameter based on sand fluxes. Adapted from van Rhee (2001). 

van Rhee (2002) noted that it is uncertain if the relationship holds for 

different scales, and it only accounts for spherical grains of uniform 

diameter. Likewise, the concentration at the bottom is not known, and 

must be approximated by the incoming concentration. 

One of the conclusions based on the laboratory study was that turbulence 

plays a lesser role in sedimentation processes within hoppers, although 

that may not hold at prototype scale. However, given the often observed 

viscous flow behavior during hopper loading stages, that conclusion may

indeed be applicable in many cases. 

For the modeling component, a one-dimensional (1D) model of hopper

sedimentation was developed using the advection-diffusion equation for a 

poly-disperse mixture, and includes the influence of the overflow rate 

(hopper load parameter). As opposed to the horizontal settling tank model 

of Camp (2001), this model simulates hopper loading in the vertical 

dimension with sediments introduced from the bottom fed by the density 

current, and the overflow located at the top. The model was compared with 

1D tests in a settling column, which showed reasonably good agreement. 

Van Rhee (2002) later developed a two-dimensional model based on the 

ERDC/CHL TR-20-8 16

2.2.1 Pipeline outfall

Pipeline outfalls associated with open water disposal of dredged material 

have been studied since the 1970s to determine potential environmental 

impacts of dredging due to suspension of sediments in the water column 

(e.g., Gordon 1974; Brandsma and Divoky 1976; Henry et al. 1978; Nichols 

and Thompson 1978). These studies were mainly focused on resuspension

and the behavior of the material to predict the extent and duration of the 

fluid mud and, ultimately, determine potential environmental impacts due 

to dredging. In subsequent studies, focus was turned to the dispersion and 

underflow of the material once it was placed in the open water. Teeter 

(1994) describes three dispersion phases of pipeline disposal of dredged

material: (1) discharge plume descent, (2) underflow spreading and 

entrainment of the underflow material into the overlying ambient flow, 

and (3) passive dispersion. The Plume Measurement System (PLUMES) 

was used at a field site in the James River Estuary in Virginia to detect 

relative concentrations, measure current fields, and chart vessel position 

during a dredging event. Suspended sediment samples were also collected 

for ground truthing. The field data indicated that the discharged sediment 

descended and reached the bed directly below the discharge point. An 

underflow formed and spread to a distance approximately 100 m from the 

source, and the spreading was controlled by the bathymetry of the site. It 

was also concluded that most entrainment would occur during higher 

current speeds.

Although no literature was found on studies regarding pipeline outfall on 

the beach, the sedimentation processes due to outfall on the beach are 

similar to those in the hopper. Sorting of sediments at the beach outfall is 

governed by the balance of particle settling and the physical processes of 

the flow. Sediments in the pumped slurry within the pipeline are kept in 

suspension by maintaining sufficiently high flow velocities (and turbulent 

mixing) in the pipe. The flow exiting the pipe plunges into a mixing cell 

and then spreads out under gravitational effects as dictated by the 

geometry of the beach and exit velocity of the flow. The beach geometry 

may be altered by temporary construction works such as berms or dikes to 

direct the outflow and/or enhance sedimentation. As the flow becomes less 

confined and spreads under gravitational forcing, velocities typically 

decrease, leading to decreased turbulent mixing and deposition of the 

suspended sediments. The degree of sedimentation is governed by factors 

such as the horizontal velocities, the beach slope, water depth in the outfall 

flow, length of the outfall flow path, and sediment settling velocity.
ERDC/CHL TR-20-8 17

2.2.1.1 Modeling of discharge from pipeline outfalls

Several models illustrate discharge at pipeline outfalls. CORMIX is a US

Environmental Protection Agency near-field mixing analysis model that 

simulates the initial mixing of the dredged material immediately upon 

submerged discharge from the dredge pipe (Doneker and Jirka 2007; MG 

Associates 2012; Purnama et al. 2016). The Pipeline Discharge FATE 

(PDFATE) model is used to evaluate underflow spreading and to predict 

the deposition of sediments on the bottom, as well as entrainment of 

sediments in the water column (Teeter 2000, 2001; MG Associates 2012).

The model formulation includes deposition of sediment particles 

according to concentration-dependent settling rates and shear stress 

thresholds related to sediment characteristics, entrainment of overlying 

water into the underflow, appropriate flow properties of the underflow 

suspension, lateral spreading of the underflow, and variable bottom slope 

(Teeter 2001; MG Associates 2012). To determine long-term fate of 

material once it deposits on the bottom, the Environmental Fluid 

Dynamics Code (EFDC) coupled with the SEDiment dynamics algorithms 

as developed by Ziegler, Lick, and Jones (SEDZLJ) model is often used 

(Ziegler and Lick 1986; Ziegler and Lick 1988; Jones and Lick 1999; Jones 

and Lick 2001). EFDC is a model for simulating three-dimensional (3D)

flow, transport, and biogeochemical processes in surface water systems 

(Hamrick 1996). EFDC was modified by the Sandia National Laboratories 

to include sediment dynamics such as erosion and bed load transport, bed 

sorting, and armoring (James et al. 2010; Thanh et al. 2008; 

MG Associates 2012). The US Army Corps of Engineers (USACE) later 

incorporated EFDC-SEDZLJ in the Long Term FATE (LTFATE) modeling 

analysis for material placed in open water (e.g., Hayter et al. 2012). These 

models are generally not applicable for subaerial pipeline outfalls on the 

beach; however, they are applicable for nearshore placement. 

2.2.2 Separation of sediment due to nearshore and beach processes 

Once material is placed on the beach, sediment separation due to natural 

beach and nearshore processes such as waves and currents can occur. The 

concept that fine material winnows out of beach sands through 

hydrodynamic or aeolian forcing is well established (e.g., Stapor and 

Tanner 1975; McCave 1978; Kana and Mohan 1998). However, recent 

studies have begun to focus on detailed monitoring of sediment 

characteristics following beach nourishments to determine if current state 

regulations regarding placing certain amounts of fines on beaches are 
ERDC/CHL TR-20-8 18

necessary (e.g., Warrick 2013, Goodrich and Warrick 2015, Maglio et al. 

2015). Generally, because fine material has a slower settling velocity than 

coarse material, once material is suspended in the water column, fine 

sediment is entrained in the orbital motions of the wave for a longer time, 

and consequently, the fine fraction of the sediment is transported farther 

offshore than the coarse fraction (e.g., Dean 1973, 1977; Hallermeier 1981).

Warrick (2013) studied a nourishment at Imperial Beach, California, 

which contained 40% fines by weight. The study showed that the mean 

residence time of fine material suspended in the surf zone through wave 

action was approximately 1 hour. Decreases in fine sediment within the 

surf zone along the beach were due to offshore transport by rip currents.

In the swash zone, because the material was placed directly on the beach, 

elevated levels of suspended fines lasted several days after nourishment as 

fine material was being winnowed from the beach. Deposition of the fine 

material was greatest on the seafloor directly offshore of the nourishment 

area; however, a mass balance of the sediment suggested that the majority 

of fine sediment was deposited over 2 km away from the nourishment site 

or to water depths greater than 10 m. The study concluded that the fate of 

fine material was strongly influenced by wave conditions, surf zone and rip 

current transport, and the vertical density and flow conditions of coastal 

waters. Goodrich and Warrick (2015) summarized this study as well as a 

study conducted at Santa Cruz Harbor. The two demonstration projects 

were used as tools to communicate with coastal managers regarding the 

use of material with relatively large amounts of fines in beach and 

nearshore nourishments.

Maglio et al. (2015) studied several beach nourishment projects in 

Florida to determine fines loss through the dredging process.

Specifically, at Egmont Key, Florida, fine material initially found on the 

surface of the beach, and in the nearshore immediately post-placement, 

was no longer seen in successive surface sediment samples along the 

profile 5 months post placement, indicating that fine sediment found on 

the surface was likely winnowed through wave-current processes and 

transported away from the beach.

2.3 Transport processes in TSHD overflow plumes 

During overflow of TSHDs, the suspended sediments passing over the 

overflow weir are introduced outside of the dredge and into the water 

column. In most cases, the overflow stream is denser than the surrounding 
ERDC/CHL TR-20-8 19 

water, and a negatively buoyant cloud or jet is formed. This dense dynamic 

plume is transported towards the sediment bed primarily by buoyancy 

effects. During the descent of the dynamic plume, ambient water is 

entrained into the plume, and the plume becomes less dense. The descent of 

the dynamic plume may be arrested by neutral buoyancy or interaction with 

the bed. During descent and interaction with the TSHD hull or propellers, 

turbulence may eject and mix smaller clouds of suspended sediment with 

cloud densities that are nearly equal to the surrounding water body. In this 

case, the settlement of the clouds can become dominated by particle 

settling. These passive plumes settle at rates governed by the size and 

density of individual particles suspended in the cloud.

2.3.1 Dynamic plume

The TSHD dynamic plume is challenging to observe and sample in the 

field environment as it is typically positioned beneath the hull of the 

moving dredge. Due to the difficulties of directly measuring the dynamic 

plume in the field, most research of the governing processes has been 

performed with physical and numerical modeling. Chu and Lee (1996) 

provide a review of theoretical physical processes of plumes and jets in 

crossflow. Winterwerp (2002) conducted experimental laboratory studies 

relating the relative importance of dynamic plume spreading by mixing 

and gravity effects. Recently, DeWit et al. (2014) expanded upon this work 

by examining the interaction of the dynamic overflow plume with the 

nearfield effects of the TSHD hull and propellers under varying 

operational parameters with a combination of physical and Computational 

Fluid Dynamics models. 

2.3.2 Passive plume

Relatively speaking, the TSHD passive plume has received much more 

attention than the dynamic flume in recent research. The passive plume is 

of interest primarily because of the slower settling rates of suspended 

sediment in the passive plume, and consequently the greater capacity for 

these suspended sediments to be transported relatively large distances 

from the dredging site. To model the passive plume appropriately, 

numerous dredge and sediment properties must be defined. At the TSHD, 

the density and overflow rate of dredged material must be determined, as 

well as the sediment size distributions. The mass exchange rate (or 

exchange fraction) between the dynamic plume and the passive plume 

must be quantified, along with the initial vertical distribution of passive 
ERDC/CHL TR-20-8 20 

plumes. Furthermore, the settling rates of suspended sediment must be 

determined. Advances in optical and acoustic instrumentation in the 

1990s permitted measurement of suspended sediment concentrations and 

sizes in dredge plumes (Kraus and Thevenot 1992; Land and Bray 2000; 

Mikkelsen and Pejrup 2000). Spearman et al. (2007, 2011) summarize 

field research performed in the early 2000s in Europe to determine the 

exchange rate between the dynamic and passive plumes. Mikkelsen and 

Pejrup (2000) documented increasing suspended particle size with 

distance from the dredging operation, suggesting that flocculation was an 

important process influencing settling rates in passive plumes. Smith and 

Friedrichs (2011) deployed their Particle Imaging Camera System (PICS) 

in a TSHD overflow plume in San Francisco Bay to measure suspended 

particle size, settling velocity, and density. Smith and Friedrichs (2011) 

found that flocculation occurred in the overflow plume and a population of 

dense bed aggregates was present, which further increased the settling 

velocity of the suspended aggregates relative to their constituent particles.

2.3.3 Modeling of the overflow plume 

The buoyancy-driven dynamic plume and the particle-settling dominated 

passive plume are governed by different physical processes operating over 

distinctly differing time- and space-scales. Consequently, numerical 

modeling of these two phases of the overflow plume is typically handled 

with separate frameworks and modules for the distinct phases. The 

required process representations for modeling the overflow plume begin 

with the overflow process of the TSHD itself. The mass rate of overflow is 

expected to vary in space and time. A model representing the variances in 

the mass rate of overflow and the composition of overflow provides the 

initial conditions for the dynamic plume. The dynamic plume model would 

then represent the descent of the plume from the overflow discharge to the 

bed or a position of neutral buoyancy in the water column. Included in this 

process would be any mixing of sediment into the water column as passive 

plumes. Finally, a passive plume model will transport suspended sediment 

contained in passive clouds until conditions permit deposition. 

The modular description of the modeling workflow described above is 

common among dredged material plume and outfall modeling (Koh and 

Chang 1973; Johnson et al. 1990; Spearman 2011). The models derived 

from these efforts (Confined Disposal Fate and Turbidity Assessment 

Software [TASS]) operate on a Lagrangian, cloud-based framework. 

Lackey and Smith (2008) applied the initial passive plume estimates of the 
ERDC/CHL TR-20-8 21

bottom dump model Short-term Fate (STFATE) as initial conditions to the 

Lagrangian Particle Tracking Model (PTM) for a navigation dredging 

study. The advantage of this approach is that the local-scale Lagrangian 

cloud models can approximate overflow and the dynamic plume while a 

high-fidelity 3D Lagrangian model (such as PTM) can represent particle 

mixing and deposition in the far field. Point-based Lagrangian models 

such as PTM offer significant advantages over the cloud-based Lagrangian 

approach, primarily through higher fidelity of transport processes over 

long distances. The coupling of appropriate hopper and dynamic plume 

models to a 3D, point-based Lagrangian sediment transport model (in the 

style of Lackey and Smith [2008]) will be further explored over the course 

of this research.

In addition to the numerical modeling framework, specific issues of finesediment separation in the hopper and fine-sediment settling velocities in 

the passive plumes must be addressed. Separation of sand and fines by 

hopper overflow is largely dependent upon the settling velocity of 

sediment particles. Sand-sized and coarser sediment particles have 

relatively large settling velocities (typically 6 mm/s or more), which allow 

them to settle in the hopper, and disaggregated fine sediments have small 

settling velocities (typically less than 2 mm/s), which allow them to be 

maintained in suspension to the overflow weir. However, fine sediments 

may be cohesive, forming aggregates that are greater in size but less dense 

than the constituent particles. The largest of these aggregates, known as 

clay balls in the dredging community, are recognized to deposit in hopper 

dredges during overflow (Palermo and Randall 1990; Burt and Hayes 

2005). However, these fine-sediment aggregates are likely to form in a 

wide range of sizes. Smith and Friedrichs (2011) documented 40–250 μm 

fine-sediment aggregates settling at rates as fast as 5 mm/s in a TSHD 

overflow plume. Smith and Friedrichs (2011) further postulated that 

larger, faster settling aggregates were likely trapped in the hopper. In fact, 

dense bed aggregates 300 μm or larger would have settling velocities 

equal to or greater than fine sand. Of course, fine-sediment aggregates 

produced during the dredging process must survive the large mechanical 

and hydrodynamic stresses of the dredging process. The strength of mud 

aggregates (Krone 1963; Kranenburg 1994) is related primarily to the 

density of particle packing (or bulk density) and the cohesion of the 

minerals (related to clay mineralogy). Considering these issues, bed 

density, fines content, and some measure associated with the cohesiveness 

of the fine-grained material may be key predictors of the target sediment’s 
ERDC/CHL TR-20-8 22 

propensity to produce fine sediment aggregates, which influences the 

separation rate of fine sediments from the desired sand.

Flocs are low-density aggregations of fine-sediment particles formed in the 

water column through inter-particle collisions and aggregation. The bonds 

formed through aggregation are initially weak, and consequently flocs are 

relatively delicate. When exposed to turbulent shear or collisions with the 

bed or other suspended particles, flocs may be broken into smaller, 

constituent particles or disaggregated completely. Therefore, flocculation

is a balance between aggregation and disaggregation. Factors favoring 

aggregation are particle concentration, turbulent shear, and particle 

cohesiveness. Factors favoring disaggregation are high turbulent shear and

floc collisions. Flocculation is relevant to the transport of the passive 

overflow plume in that as particle sizes increase, so do settling velocities. 

Therefore, flocculation can lead to decreased transport distances and 

increased sedimentation rates surrounding the dredging site compared to 

the case of completely disaggregated fine sediment. Mikklesen and Pejrup 

(2001) and Smith and Friedrichs (2011) have observed particle sizes of fine 

sediment increasing with time in passive overflow plumes, suggesting that 

flocculation can occur in these situations. Smith and Friedrichs (2011) 

further observed that the increase in particle size with flocculation led to a 

doubling of settling velocity over a period of 80 min. Size and settling 

velocity of suspended particles in the passive plume will be quantified in 

the subject research in such a way as to inform the numerical modeling of 

these processes.

2.4 Sampling methods

The primary aim of sediment sampling is to determine sediment size 

distributions and mass concentrations at all stages in the dredging, 

transport, and placement process. Ample guidance is available on the 

sampling of bed materials and suspended loads within riverine and coastal 

environments. However, guidance for sampling from hopper dredgers is 

generally lacking, and the majority of what is known from the literature 

originates from a few studies. This section reviews the proposed methods 

for sediment sampling and processing to characterize bed materials at the 

borrow and placement sites, tracking the size and quantity of sediments 

entering and exiting the hopper dredge, and characterizing the sediment 

plume of the dredger. These methods include direct physical sampling and 

indirect surrogate monitoring using instrumentation. 
ERDC/CHL TR-20-8 23 

2.4.1 Bed material sampling 

To determine the proportion of fine sediments lost in the process of 

dredging and placement, it is necessary to collect samples at both borrow 

and placement sites. Accurately quantifying the loss of fines through 

dredging requires an accurate characterization of bed materials at the 

dredge site. Bed materials at depth are often collected through the use of 

grab, drag, or core-type samplers; the suitability of each depends on the 

in situ grain size, consolidation, water depth, required sample volume, and 

the necessity to recover an undisturbed versus disturbed sample. 

2.4.1.1 Grab samplers 

Grab samplers (e.g., Shipek and Van Veen samplers) are clamshell-style 

gravity samplers that have opposing jaws to scoop and retain surficial 

sediments. The jaws are closed upon impact with the bottom by weights, 

springs, or cords. These samplers work best for fine sediments as coarser 

sediments generally prevent the jaws from closing properly. The 

penetration depth of most grab samplers is approximately 10–15 cm while 

sample volumes are typically 3–15 L depending on sampler dimensions.

2.4.1.2 Drag samplers 

For coarser sediments, a drag sampler is sometimes more appropriate. A 

drag sampler used by field workers at the US Army Engineer Research and 

Development Center, Coastal and Hydraulics Laboratory, uses a steel pipe 

approximately 1 m long, closed on one end, 10 cm in diameter flaring to 20 

cm on the open end. The sampler is allowed to drag behind a moving 

vessel using a length of rope 2–3 times the water depth to keep the 

sampler horizontal. An advantage of the drag sampler is that the retrieved 

sample may better represent the average bed composition at the surface 

because the sample is taken across a larger spatial extent. For this project, 

however, the penetration depth should exceed the expected dredging 

depth to obtain a representative composite sample. A disadvantage of this 

sampler is that it remains open, potentially losing some fine material 

during retrieval. 

2.4.1.3 Core samplers 

Coring devices are used to take relatively undisturbed bed samples. 

Penetration into the surface is accomplished using gravity as they are 

heavily weighted. Box corers typically penetrate between 0.4 to 0.75 m and 
ERDC/CHL TR-20-8 24

yield sample volumes from 10 to 200 L. Once at the penetration depth, a 

cable releases a closing shovel underneath the box before retrieval. 

Similarly, free-fall corers use a weighted stainless steel tube fitted with a 

cutting head to penetrate the sediment and steering fins to keep the corer 

vertical. Sediment is captured within a plastic casing, and sample loss is 

prevented by means of a core catching device at the opening and flaps that 

seal off the core surface. 

Sediment sampling at the nourishment area following pump out can be 

achieved through the use of vibracoring. Cores should be taken in the 

moist state to prevent collapse and at a sufficient depth to capture the 

horizon between native and placed sediments. The entire portion of the 

core above the horizon should be retained to maintain sample 

representativeness so that an appropriate subsample can be prepared for 

grain size analysis. 

The sampling scheme specific to this project will be outlined in the field

experiment plan based on the completion of the literature review and 

laboratory experiment. 

2.4.2 Overflow weir sampling 

Reliable measurements of the solids concentration passing an overflow 

weir may only be achieved through direct sampling, as turbulence, 

bubbles, and vertical gradient of sediment concentration prohibit the use 

of surrogate monitoring via sensors (HR Wallingford 2003). Sampling of 

the overflow weir may be accomplished using bottle, flow-through, or 

pump samplers. 

2.4.2.1 Bottle sampling

Bottle samplers, in their most basic form, use a collection bottle attached

to a dipping pole or rope to extract a sample. Kerssermaker (2004) used a 

modified version to sample the overflow weir of the hopper dredge 

Cornelia. Here, a 1.0 L bottle was placed within a steel container and, 

using a rope, lowered to a depth of approximately 30 cm at the center of 

the overflow pipe. A second rope was used to open the lid of the steel 

container once in position; approximate fill times varied between 2 s and 

6 s. Sample contents were transferred to a separate container; then the 

bottle was flushed with a known water volume to remove residual 

sediments. This volume is later subtracted for concentration calculations. 
ERDC/CHL TR-20-8 25 

Given the simplicity of this method, a high sampling frequency can be 

achieved. A considerable disadvantage is that it cannot be known precisely 

when the bottle is filled; overfilling the bottle likely results in sample bias 

(Kessermaker 2004).

2.4.2.2 Flow-through sampling

The flow-through sampler allows a sediment-water mixture to pass from 

the front to the rear of the sampler, ideally without accelerating 

(isokinetic). This type of sampler was also used by Kessermaker (2004) 

to compare mass concentrations of samples taken using the bottle 

sampler. The flow-through sampler consisted of an aluminum body with 

dimensions 40 × 20 × 5 cm giving a sample volume of 4 L. This custom 

sampler used rubber-sealed doors held open at the ends using elastic 

bands that close using a release cord. When closing, the timing of the 

doors was slightly offset to increase volume capture since the sampler is 

not completely submerged. The flow-through samplers were deployed 

using guide ropes attached to the outer flange of the weir pipe parallel to 

the direction of flow (Figure 6). Kerssermaker (2004) reported that each 

sample took approximately 3–4 min to obtain; at least 10 samples are 

needed to characterize the overflow period (HR Wallingford 2003). 

Using a rotation of three crews and three samplers, a sampling rate of 

one per minute was achieved, a total yield of 30–50 samples per 40 min 

overflow period. 

Figure 6. Photo of the custom flow-through sampler used by Kerssermaker (2004). 

Image on the right shows the sampler deployed on the bell mouth of an overflow weir. 

Figure adapted from HR Wallingford (2003).

There was a concern that turbulence generated around the sampler’s 

opening meant that the flow into the sampler was not likely isokinetic, 

which may bias the sample. Additionally, this method appeared to be 
ERDC/CHL TR-20-8 26 

somewhat cumbersome in that it required a crew of 10 to collect samples 

at the aforementioned rate (HR Wallingford 2003). 

2.4.2.3 Pump sampling

Pump sampling draws a sample into a collection bottle by applying a 

vacuum to a sampling tube. The sampling tube should be completely 

submerged and placed in a zone where the slurry is well mixed. Guidance 

on pump sampling of open channel flows suggests that the orientation of 

the intake be pointed downstream relative to flow direction to maximize 

sample representativeness (Gray and Landers 2014). This implies that the 

intake be pointed vertically downward within the throat of the overflow 

pipe and lowered to a sufficient depth to minimize air entrainment. The 

diameter of the sampling tube should be chosen such that velocities within 

it are high enough to prevent sedimentation. Bosman et al. (1987) 

suggested an intake velocity three times greater than the ambient fluid 

velocity (they were measuring sediment concentrations under waves). 

However, pump sampling is not recommended according to some 

guidelines, stating that significant errors may arise due to momentum 

effects (HR Wallingford 2003). Additionally, the limited diameter of the 

intake tube would not be able to capture a vertically integrated sample 

since the flow depth over the weir may be up to 30 cm (HR Wallingford 

2003). To overcome this, an open-ended housing could be fabricated that 

attaches to the intake of the tube from which a representative sample is 

drawn. Such modified pump sampling devices are under consideration for 

the laboratory sampling evaluation.

2.5 Uncertainty in quantifying losses

With any experimental endeavor comes measurement error and 

uncertainty. It is incumbent upon the researcher to communicate estimates 

of the uncertainties in the measurements of the research. The researchers 

on this team will quantify the measurement uncertainties following the 

principles of error analysis (Taylor 1997). This exercise will be completed 

during the experimental planning phase of the research, and will be 

documented in the field experiment plan. The field uncertainty estimates 

will incorporate findings of the laboratory evaluation of sampling methods

and then later results of the field measurements themselves. 
ERDC/CHL TR-20-8 27

3 Conclusions and Recommendations

3.1 Conclusions

Models exist for representing the settling rate of sandy sediments in TSHD 

hoppers. While these models have shown some skill in representing 

specific dredging operations, they are limited in their capacity to predict 

the quantity of fines lost during the dredging process because particle size 

distributions are currently undetermined without direct sampling. Having 

particle size distribution information would prove valuable not only in 

predicting the loss of fines but also in developing a comprehensive source 

term for modeling the fate of overflow plumes. 

Additionally, research is required to quantify the propensity of fine 

sediments, particularly those with appreciable clay content, to form robust 

aggregates that settle at rates comparable to that of sand. These aggregates 

could significantly increase the retention of fine-grained sediments in the 

hopper in some instances. Research is needed to characterize the 

flocculation propensity of fines separated from sandy materials during 

hopper overflow. Previous research (Mikkelsen and Pejrup 2000; Smith 

and Friedrichs 2011) has identified flocculation as a first-order process in 

passive overflow plumes. Smith and Friedrichs (2011) further determined 

that settling velocities in suspension doubled in a period of just over an 

hour due to flocculation of the suspended sediment.

A modeling framework was discussed for representing transfer of

sediment from the hopper overflow to the water column in suspension. 

The framework involves modular near-field models of the hopper 

retention and overflow process, followed by cloud-based Lagrangian 

representation of the dynamic plume. The dynamic plume model will then 

generate initial conditions of the passive plume clouds of suspended 

sediment. The passively transported sediment can be represented with 3D 

point-based Lagrangian methods, such as the PTM. This approach has 

been demonstrated previously by Lackey and Smith (2008) with a bottom 

dumping operation with STFATE generating the initial cloud conditions 

for PTM.

Previous research regarding sediment dispersion at a pipeline outfall is 

primarily related to open water disposal of sediment and the fluid mud 

flows that occur at the bed as a result. Models exist to demonstrate this 
ERDC/CHL TR-20-8 28 

mixing and dispersion; however, they do not show the separation of fine 

material specifically. On the beach, there have been studies that aim to 

quantify fines loss through natural beach processes. However, there have 

not been studies that combine fines loss through the pipeline outfall with 

placement on the beach. Hence, more investigation into the fines loss 

during the outfall and return water resulting from the slurry needs to be 

completed.

3.2 Proposed research

The objectives of the broader effort are to quantify sediment sorting 

during hopper dredging and pump-out operations of sandy sediments 

containing fine-grained silt and clay. The research aims to associate 

contributing factors such as dredging operations, environmental 

conditions, and sediment characteristics with separation rates of sediment 

classes in the dredging process. The mass transfer rates by size class will 

be quantified in each of the potential exchange points with the water 

column: (1) the draghead, (2) overflow, and (3) pump out. Additionally, 

the suspended sediment characteristics of sediments introduced to the 

water column are to be determined in a manner that facilitates bounded 

estimates of ultimate transport and fate of these sediments. The research 

is being executed in defined tasks focused on specific research 

requirements. Each of these efforts is described in greater detail in the 

following sections.

3.3 Conceptual model and literature review

A conceptual model of the governing processes has been developed and is 

discussed in this present report. The purpose of this task is to present the 

present state of understanding for the physical processes controlling 

separation of sediments during the TSHD process from dredging site to 

pump out, and reworking of the relocated sediments. As part of this process, 

specific research needs are identified. These needs are developed and 

justified in Chapter 2 Conceptual Model. The remaining tasks will 

incorporate the associated research requirements into their workflow.

3.4 Sampling methods

Sampling suspended sediments from the inflow stream and overflow weirs 

of an operating hopper dredge is challenging due to high-velocity flows 

and temporal and spatial variabilities in both the flows and sediment 
ERDC/CHL TR-20-8 29 

concentrations. A testing basin has been designed and is presently under 

construction for evaluating candidate sampling procedures. The sampling 

methods will be evaluated through controlled laboratory experiments 

considering sampling methods, sampling locations, sampling containers, 

sampling frequency, and dredged material composition. The sampling 

methods investigation will also evaluate sample compositing and sample 

splitting schemes.

Based in part on the laboratory evaluation, a written sampling plan will be 

developed. The sampling plan will be developed to determine (1) 

appropriate sampling techniques, (2) the appropriate sample size and 

number to obtain statistically significant results under field conditions, (3) 

the expected uncertainty in the field measurement plan, and (4) sampling 

requirements for supporting sediment tracking models (such as water 

chemistry and physical sediment characteristics and processes).

3.5 Field measurements of sediment sorting during dredging 

operations

Sediment separation and fractionation during dredging operations will be 

determined from field sampling campaigns of offshore sand mining and 

navigation maintenance dredging operations. These field sampling 

campaigns will be conducted on both USACE and contract dredges. The 

aim of these measurements will be to determine the relationships between 

sediment sorting during the dredging process, and physical sediment 

properties and dredge characteristics. Sampling locations are associated 

with the exchange points of the dredging process, including the sediment 

bed at the dredging site, the inflow and outflow of the hopper dredge 

during dredging and overflow, the hopper discharge during pump out, and 

the beach. These locations will be sampled according to the experiment 

and sampling plan. Additionally, the settling velocity and dynamics of the 

suspended surface overflow plume will be quantified. Execution of field 

measurements was scheduled between summer 2017 and summer 2018.

Associations will be examined between the dredge characteristics, 

sediment characteristics, and the separation of sediments in the hopper 

during overflow and pump out. Existing models of hopper settling and 

overflow will be evaluated with the collected data, and new models will be 

devised and evaluated if necessary.
ERDC/CHL TR-20-8 30 

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Appendix: Annotated Bibliography of 

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Overview of Hopper Dredges

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Certain Aspects of Their Design.” Marine Technology 20 

(2): 164-176. 

This journal article gives an overview of trailing suction hopper dredges, 

their design characteristics and classification, and includes a summary of 

the dredging subsystems: drag arm, pumps, discharge, overflow, dumping, 

pump-out, subsystems. Other useful information includes schematic 

diagrams of various vessels and a table of physical attribute data, including

dredge pump characteristics.

Separation of Sediment by Hopper Dredging

Camp, T. R. 1936. “A Study of the Rational Design of Settling 

Tanks.” Sewage Works Journal 8(5): 742–758. 

This journal paper concerns the development of a sedimentation theory 

within an ideal settling tank, with flow entering one side and exiting the 

other. Originally constructed for sewage engineering works, Camp’s theory 

is cited as the basis for settling theory and overflow losses within hopper 

dredges. The ideal settling tank assumes that (1) the flow is horizontal and 

uniform, (2) a uniform concentration of particles in a vertical plane 

perpendicular to flow, (3) each particle is independent and settles at a 

constant velocity, and (4) particles are removed when they strike the 

bottom (hence no sediment accumulation). One caveat is that the 

horizontal velocity should not cause scour. 

Miedema, S. A., and W. J. Vlasblom. 1996. “A Theory for 

Sedimentation in Hoppers.” 29th Annual Texas A&M 

Dredging Seminar. New Orleans, Louisiana, USA.

This work is a follow up to the previous work by Vlasblom and Miedema 

(1995). Modifications to the previous work include modification of some 

equations for turbulent settling efficiency resulting in different hopper 

loading curves and a change to the implementation of scour velocity. 
ERDC/CHL TR-20-8 36 

Noted was the difficulty in obtaining field data to verify the model, which 

include loading curves and grain size distributions of the sediment within 

the overflow. No discussion was provided in terms of the percent loss of 

the total load or the percent loss of fines.

Miedema, S. A., and C. van Rhee. 2007. “A Sensitivity Analysis 

on the Effects of Dimensions and Geometry.” WODCON 

XVIII. Orlando, Florida, USA.

This work compares the results between the models used in Vlasblom and 

Miedema (1995) based on simplifying Camp’s equations, and a twodimensional model (horizontal and vertical directions) developed by van 

Rhee (2001), which is based on Reynolds-averaged Navier-Stokes 

equations. Differences in the overflow losses and loading times are 

discussed. The results between the two models were not drastically 

different. 

Miedema, S. A. 2010. “The Effect of the Bed Rise Velocity on the 

Sedimentation Process in Hopper Dredges.” WODCON 

XIX. Beijing, China. 

This work investigates the influence of the bed rise velocity on the hopper 

load parameter since this influences settling time. A secondary research 

topic examined potential scaling laws from small to large capacity 

hoppers, which determined to keep the hopper load parameter constant 

and derive other scale laws for the flow and not to scale the sand.

Ooijens, S. 1999. “Adding Dynamics to the Camp Model for the 

Calculation of Overflow Losses.” Terra et Aqua 76: 1–21. 

This paper modifies the model of Vlasblom and Miedema (1995) by adding 

a time effect by considering a dynamic input of flow volume and slurry 

concentration. This is different from the previous models as the outflow 

concentration is based on instantaneous settling efficiency based on the 

inflow concentration. The model appeared to capture the estimated total 

overflow loss reasonably well for two of three dredging test cases (reported 

correlation of 0.75 to 0.85). 
ERDC/CHL TR-20-8 37

Vlasblom, W. J., and S. A. Miedema. 1995. “A Theory for 

Determining Sedimentation and Overflow Losses in 

Hoppers.” Proceedings, WODCON XIV. Amsterdam, The 

Netherlands. 

Published in the proceedings for WODCON 1995, this work modifies 

Camp’s (1936, 1946) theory for ideal settling tanks but included a grain 

distribution as opposed to using a single grain size, a sedimentation zone, 

hindered settling, and adjustable overflow. The model is run on a 

computer program called TSHD (Medina 1991), which aims to determine 

the settling efficiency (a function of the settling velocity to horizontal flow 

ratio) for individual grain sizes and the evolution of the grain size 

distributions in time through the overflow and at the top of the 

sedimentation zone. An analytical treatment of the settling processes are 

provided along with a case study using three sand distributions (d50 = 

0.10, 0.30, and 1.0 mm) and hypothetical hopper dimensions, flow rate, 

mixture density, and loading cycle times. The primary objective was to 

estimate an optimal hopper loading time and overflow losses. No 

discussion is provided in terms of the percent loss of the total load or the 

percent loss of fines.

van Rhee, C. 2001. “Numerical Simulation of the Sedimentation 

Process in a Trailing Suction Hopper Dredge.” 

Proceedings, WODCON XVI. Kuala Lumpur, Malaysia. 

The primary aim of this work was to understand the sedimentation 

process during hopper loading. The rationale for the study concerns the 

economic payload, that some sand will be discharged in the overflow 

mixture. Both laboratory experiments and numerical modeling were used 

to investigate the sedimentation processes. Detailed observations of 

settling and flow processes were observed during the experiments. The 

modeling component uses a more complex schematization of the hopper 

sedimentation processes than that of Vlasblom and Miedema (1995). 

The amount of fine material lost in the overflow was quantified over 19 

experiments. The experiments showed that cumulative overflow losses 

could be expressed as a linear function of the hopper load parameter, 

which is proportional to the discharge per unit surface area into the 

hopper and inversely proportional to the sedimentation velocity of the 

suspension (i.e., hindered settling given by the Richardson and Zaki [1954] 
ERDC/CHL TR-20-8 38 

formulation). This linear relationship was found to improve if the load 

parameter was based on sand fluxes (ratio between the inflow fluxes and 

settling fluxes). The authors noted that it is uncertain if the relationship 

holds for different scales and it only accounts for spherical grains of 

uniform diameter.

Separation of Sediment by Pipeline Outfall and Beach Processes

Goodrich, K. A., and J. A. Warrick. 2015. “Fines: Rethinking Our 

Relationship.” Proceedings, Coastal Sediments 2015.

Two studies where dredging projects contained a relatively large percentage 

of fines were summarized. The Santa Cruz Harbor demonstration project 

placed material with up to 71% fines by weight in the nearshore, and the 

Tijuana River demonstration project placed material with 40% fines by 

weight on the beach. Both projects aimed at seeing whether relatively large 

proportions of fines had any negative impact on the beach. Results from the 

Santa Cruz project showed that the energetic conditions of the ocean quickly 

moved the fine material farther offshore. The Tijuana River project showed 

that fines had approximately a 1-hour residence time in the surf zone and 

then subsequently moved far away (approximately 2 km) from the 

nourishment area. The paper also summarized outreach efforts to the 

coastal management community in California.

Teeter, A. M. 1994. “Dredged Material Dispersion from the Vicinity of 

Pipeline Discharge, Tylers Beach, Virginia.” Proceedings of the 

Second International Conference on Dredging and Dredged 

Material Placement, 918-927.

A submerged pipeline discharge of hydraulically dredged sediment in 

Tylers Beach, Virginia, was studied. The PLUMES was used at a field site 

to detect relative concentrations, measure current fields, and chart vessel 

position during a dredging event. Suspended sediment samples were also 

collected for ground truthing. The field data showed that the discharged 

sediment descended and reached the bed directly below the discharge 

point. An underflow formed and spread to a distance approximately 100 m 

from the source, and the spreading was controlled by the bathymetry of 

the site. The paper gives an overview of the dispersion process including 

the discharge plume descent, the underflow spreading and entrainment of 

the underflow material into the overlying ambient flow, and the passive 

dispersion of the material.
ERDC/CHL TR-20-8 39 

Teeter, A. M. 2000. Underflow Spreading from an Open-Pipeline 

Disposal. ERDC TN-DOER-N7. Vicksburg, MS: US Army 

Engineer Research and Development Center.

This technical note summarizes the mixing and dispersion processes 

associated with open-water pipeline discharges from hydraulic dredging 

operations. Specifically, it discusses the underflow plume spreading of 

disposed dredged material. The underflow is a layer of fluid mud on the 

bottom that flows away from the point of discharge, depending on bottom 

slope, ambient currents, and their initial discharge trajectory. The paper 

also describes the entrainment process of sediment from the fluid-mud 

layer into the water column, as well as factors contributing to turbidity 

generation (including spreading or stripping of material at the water 

surface, gas entrained in the dredged material and released during 

disposal, stripping of material by the water column during descent, and 

entrainment of material by the water column during underflow spreading.

The paper also begins discusses an analytical model that was developed to 

illustrate the spreading of the underflow layer.

Teeter, A. M. 2001. Simulating Underflow Spreading from a ShallowWater Pipeline Disposal. ERDC TN-DOER-N11. Vicksburg, MS: 

US Army Engineer Research and Development Center.

This technical note is a follow on to the Teeter (2000) technical note where 

the computation model for simulating underflow from a pipeline discharge 

in shallow water is described. The model computes sediment flux, total 

flow or discharge breadth, and height along the length of the underflow.

These state variables are calculated by numerically integrating a set of 

governing equations downslope in the direction of the underflow. The 

Pipeline Disposal Model (PDFATE) can use a single grain class (PDFATEs)

or multiple grain classes (PDFATEm), but does not include near-field 

processes directly because they are assumed to be known or calculated 

using a separate nearfield model such as CD-CORMIX. PDFATEm can be 

connected to SSFATE (Suspended Sediment Fate) to compute entrainment 

of disposed material into the overlying water column and subsequent 

plume dispersion by currents. The initial results from the PDFATEs agree 

well with features observed in the field. At the time of the writing, 

additional data were needed to validate the PDFATEm model. 
ERDC/CHL TR-20-8 40 

Warrick, J. A. 2013. “Dispersal of Fine Sediment in Nearshore Coastal 

Waters.” Journal of Coastal Research 29(3): 579–596.

A study was conducted on a nourishment at Imperial Beach, California, 

which contained 40% fines by weight. It was found that the mean 

residence time of fine sediment in the surf zone was approximately 1 hour, 

and rapid decreases in the surf zone alongshore were transported offshore 

by turbid rip heads. A mass balance of the sediment suggested that the 

majority of fine sediment was deposited 2 km away from the nourishment 

site or to water depths of greater than 10 m. Because fine sediment was 

being winnowed from the beach through natural beach and nearshore 

processes, elevated levels of fines were observed in the swash zone. The 

study concluded that the fate of fine material was strongly influenced by 

wave conditions, surf zone and rip current transport, and the vertical 

density and flow conditions of coastal waters.

Transport Processes in TSHD Overflow Plumes

de Wit, L., C., van Rhee, and A. Talmon. 2014. “Influence of Important 

Near Field Processes on the Source Term of Suspended 

Sediments from a Dredging Plume Caused by a Trailing Suction 

Hopper Dredger: The Effect of Dredging Speed, Propeller, 

Overflow Location, and Pulsing.” Environmental Fluid 

Mechanics 15(1): 41–66. 

Laboratory and large eddy simulation experiments were performed to 

evaluate the influence of dredging operational parameters (vessel speed, 

overflow position, propeller, and overflow pulsing frequency) on near-field 

mixing of the dynamic plume. The hull position of overflow and relative 

speed of water to the hull significantly influenced the attachment of the 

dynamic plume to the hull and consequently the mixing of sediments into 

a lower-density, passive, surface plume. The study indicates a potential 

wide variation in the fraction of sediment stripped from the dynamic 

plume, ranging from 0 to 2 percent under typical conditions to a 

maximum of 18 percent.
ERDC/CHL TR-20-8 41

Mikkelsen, O. A., and M. Pejrup. 2000. “In Situ Particle Size Spectra 

and Density of Particle Aggregates in a Dredging Plume.” 

Marine Geology 170: 443–459.

A field study in a dredging plume in the sound Øresund between Denmark 

and Sweden measured suspended particle sizes in a passive dredge plume 

with a Laser In-Situ Scattering and Transmissometry (LISST) particle sizer.

Particle sizes in suspension increased from approximately 40 μm to 

approximately 110 μm over a distance of 1.5 km and a time scale of 50 min.

This study was the first showing that flocculation processes occur in dredge 

plumes over short time- and space-scales. The implication of flocculation in 

passive plumes is that fine sediments settle faster from suspension, 

reducing the distance that these sediments travel from the dredging activity 

but increasing sedimentation close to the dredging activity.

Spearman, J., A. DeHeer, S. Aarninkhof, and M. Van Koningsveld. 

2011. “Validation of the TASS System for Predicting the 

Environmental Effects of Trailing Suction Hopper Dredgers.” 

Terra et Aqua 125: 14–22.

The TASS is described, including field measurements of hopper overflow 

conducted on a sand mining TSHD. The numerical model includes a 1D 

vertical model of the hopper and cloud-based Lagrangian models of the 

dynamic and passive plumes. 

Smith, S. J., and C. T. Friedrichs. 2011. “Size and Settling Velocities of 

Cohesive Flocs and Suspended Sediment Aggregates in a 

Trailing Suction Hopper Dredge Plume.” Continental Shelf 

Research 31: S50–S63.

A field study is presented for passive plumes generated during overflow of 

the TSHD Essayons in San Francisco Bay. Measurements of suspended 

sediment size and settling velocity were made with a LISST particle sizer 

and the PICS. The study found that the passive plume was initially wellaggregated (less than 20 min after overflow), and flocs in suspension 

continued to increase in size and settling velocity over the observation 

period (90 min after overflow). Also documented were 40–250 μm finesediment aggregates with inferred densities near that of the bed sediments 

settling at rates as fast as 5 mm/s in a TSHD overflow plume. Smith and 

Friedrichs further postulated that larger, faster settling aggregates were 
ERDC/CHL TR-20-8 42 

likely trapped in the hopper. In fact, dense bed aggregates 300 μm or 

larger would have settling velocities equal to or greater than fine sand. The 

implications of these observations are that due to cohesive effects, some 

fine sediments that otherwise would have been lost in the overflow are 

retained in the hopper. Additionally, these sediments settle 2-200 times 

faster from the passive overflow plume than their constituent particles.

Winterwerp, J. C. 2002. “Near-Field Behavior of Dredging Spill in 

Shallow Water.” Journal of Waterway, Port, Coastal, and 

Ocean Engineering 128: 96–98.

Laboratory experiments were conducted to determine the relative spread 

of the dynamic plume under the influence of gravitational (buoyancy) and 

turbulent mixing effects. Expressions for the time-dependent radial 

dispersion of the dynamic overflow plume are given for two regimes: 

gravity-driven and mixing-driven conditions.

Sampling Methods

Dredging Research Ltd., HR Wallingford. 2003. Protocol for the 

Field Measurement of Sediment Release from Dredgers. 

http://el.erdc.usace.army.mil/dots/accord/ index.html

This document provides guidance regarding the protocols and 

measurement methods of sediment plumes generated by dredging 

operations. Chapter 2.6 gives an overview of TSHD release mechanisms 

while Chapter 7 focuses on measuring TSHD overflow. The rate of 

overflow is typically measured indirectly using shipboard instrumentation 

via the inflow rate (as they should be equivalent during overflow) due to 

turbulence and air entrainment, which prevents direct measurement at the 

weir. In contrast, the solids concentration was measured directly from 

water sampling at the weir. The frequency of sampling was suggested as 

often as possible, approximately 30–50 samples per 40 min overflow 

period. Other guidance includes a checklist of supporting data that should 

be recorded for each dredging cycle (Appendix B5).
ERDC/CHL TR-20-8 43 

Kerssemakers, K. A. 2004. Overflow Sampling of Trailing 

Suction Hopper Dredgers: A Case Study on the TSHD 

Cornelia. M.S. Thesis, Delft University of Technology. 

A primary goal stated in this thesis was to determine if the solids 

concentration from the overflow weirs of hopper dredges could be 

accurately measured. Other pertinent focus questions were related to 

sampling techniques, prediction of sediment concentrations using TDS 

systems, and sampling frequency. Useful descriptions of sampling 

methods used in the field were discussed in detail, which included two 

different geometries of flow-through samplers and a bottle-type sampler. 

Variances in sediment compositions pulled from the overflow were 

compared by sampler type for consistency. 
ERDC/CHL TR-20-8 44

Unit Conversion Factors

Multiply By To Obtain 

cubic feet 0.02831685 cubic meters

cubic inches 1.6387064 E-05 cubic meters

cubic yards 0.7645549 cubic meters

feet 0.3048 meters

gallons (US liquid) 3.785412 E-03 cubic meters

microns 1.0 E-06 meters

miles (nautical) 1,852.0 meters

miles (US statute) 1,609.347 meters

miles per hour 0.44704 meters per second

ounces (mass) 0.02834952 kilograms

ounces (US fluid) 2.957353 E-05 cubic meters

pounds (mass) 0.45359237 kilograms

quarts (US liquid) 9.463529 E-04 cubic meters

square feet 0.09290304 square meters

square miles 2.589998 E+06 square meters

square yards 0.8361274 square meters

tons (2,000 pounds, mass) 907.1847 kilograms

tons (2,000 pounds, mass) per square foot 9,764.856 kilograms per square meter

yards 0.9144 meters
ERDC/CHL TR-20-8 45 

Acronyms and Abbreviations

1D one-dimensional

3D three-dimensional

CTS constant tonnage system

CVS constant volume system

EFDC Environmental Fluid Dynamics Code 

LISST Laser In-Situ Scattering and Transmissometry 

PDFATE Pipeline Discharge FATE 

PICS Particle Imaging Camera System 

PLUMES Plume Measurement System 

PSD particle size distribution

PTM Particle Tracking Model 

SEDZLJ Ziegler, Lick, and Jones model

STFATE Short-term Fate

TASS Turbidity Assessment Software 

TDS tons dry solid

TSHD trailing suction hopper dredgers 

USACE US Army Corps of Engineers 
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1. REPORT DATE

May 2020

2. REPORT TYPE

Final Report

3. DATES COVERED (From - To)

4. TITLE AND SUBTITLE

Sediment Sorting by Hopper Dredging and Pump-Out Operations:

Conceptual Model and Literature Review

5a. CONTRACT NUMBER

5b. GRANT NUMBER

5c. PROGRAM ELEMENT NUMBER

6. AUTHOR(S)

Anthony M. Priestas, S. Jarrell Smith, and Katherine E. Brutsché

5d. PROJECT NUMBER

5e. TASK NUMBER

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7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)

Coastal and Hydraulics Laboratory

US Army Engineer Research and Development Center

3909 Halls Ferry Road

Vicksburg, MS 39180-6199

8. PERFORMING

ORGANIZATION REPORT

NUMBER

ERDC/CHL TR-20-8

9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES)

Regional Sediment Management Program 

3909 Halls Ferry Road 

Vicksburg, MS 39180-6199

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RSM

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Approved for public release; distribution is unlimited.

13. SUPPLEMENTARY NOTES

Funding Account Code D86F00; AMSCO Code 008303

14. ABSTRACT

Dredged sediment placed on beaches or nearshore environments is customarily evaluated for compatibility with the native beach

sediment to avoid unintended impacts to economic, environmental, or recreational resources. Consequently, some state regulatory 

authorities establish limits upon the fine-grained content for sediment designated for placement on certain beaches and nearshore 

environments. Hopper dredging operations for beach and nearshore placement typically include periods of overflow, which is recognized 

to produce some degree of separation between the size fractions of the dredged sediment. The degree of separation and the controlling 

factors of separation are presently poorly known and are the subject of this research. This report provides a conceptual model of the 

hopper dredging and placement processes, including the relevant processes associated with hopper dredge-associated sediment dynamics, 

generation and transport of the overflow sediment plume, and sediment winnowing at the beach outflow. Prior research is described, and 

knowledge gaps are identified. Finally, a research plan to validate prior research and to address knowledge gaps is presented. An 

annotated bibliography of relevant literature is given in an appendix. Documentation of the planned research presented herein will appear 

in future publications associated with this study.

15. SUBJECT TERMS

Beach erosion, Dredges, Dredging, Particle size determination, Sedimentation and deposition, Sediment transport, Shorelines

16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF

ABSTRACT

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