Model studies of transport of sedimentary material in the western Baltic

www.elsevier.com/locate/jmarsys

Journal of Marine Systems 52 (2004) 167–190

Model studies of transport of sedimentary material

in the western Baltic

Christiane Kuhrts, Wolfgang Fennel*, Torsten Seifert

Institut fur Ostseeforschung Warnemunde an der Universitat Rostock, D-18119 Warnemunde, Germany

Received 25 March 2003; accepted 18 March 2004

Available online 17 July 2004

Abstract

The theoretical description of sedimentation, resuspension and transport of sedimentary material is an important prerequisite

for the modeling of the benthic–pelagic interaction, the impact of dumping on the coastal environment and the fluxes of

material from coastal areas into the deep basins. The present study aims at model studies of the transport of sedimentary

material in parts of the Baltic Sea and is based on a model system which links a general ocean circulation model (Modular

Ocean Model, MOM 3) adapted to the Baltic, a wave model, a bottom boundary and a sediment transport model. Several model

simulations are carried out in order to analyze the spatial distribution of the bottom shear stress in response to varying forcing

conditions. Regions of high and low bottom shear stresses as well as potential areas for erosion are identified. Further transport

and deposition patterns of different materials under varying forcing conditions are studied. We find significant seasonal

variations of the calculated transport rates. Potential accumulation areas of fine material, which corresponds to fluffy layers or

dormant stages (cysts), are investigated. The simulation shows that the material accumulates at the slopes of the basins within a

few weeks under winter conditions.

D 2004 Elsevier B.V. All rights reserved.

Keywords: Numerical model; Sediment transport; Resuspension; Accumulation; Baltic Sea

1. Introduction The complex physical processes related to sedimen-

An important issue in modeling marine ecosystems

is a quantitative description of the transport and

deposition of sedimentary material. To approach this

goal, elaborated theoretical representations of the

physical and biogeochemical processes at the seabed

and in the uppermost part of the sediments are needed.

This paper focuses on the relevant physical processes

governing the transport of the sedimentary material.

0924-7963/$ - see front matter D 2004 Elsevier B.V. All rights reserved.

doi:10.1016/j.jmarsys.2004.03.005

* Corresponding author.

E-mail address: [email protected]

(W. Fennel).

tary transports involve advection and mixing within

the water column as well as the dynamics of the bottom

boundary layer (BBL hereafter). The general features

of the hydrodynamical processes near the seabed are

well known (see, e.g. Fredsoe and Deigaard, 1992;

Nielsen, 1992a; Soulsby, 1997) and can be summa-

rized as follows. Near bottom flows and, in shallower

areas, waves generate bottom shear stresses in the

BBL. If the bottom shear stress exceeds the critical

values for bed load transport or resuspension, the

sediment is mobilized from the seabed and enters the

BBL. The sedimentary material can be either trans-

ported in suspension or as bed load. When the bottom

C. Kuhrts et al. / Journal of Marine Systems 52 (2004) 167–190168

shear stress falls below a critical value, the amount of

suspended sediment diminishes while deposition of the

material commences. The critical values for bed load

transport, resuspension and deposition are material

properties of the sediment, which depend on specific

factors such as grain size and compaction. These

properties must be determined from observations in

laboratory experiments or in situ near the seabed.

To include these processes into a circulation model,

an adequate description of the BBL is required. The

dynamics of the BBL is governed by near-bed inter-

actions of waves and currents. The near bed flows as

well as the bedform can be affected by moving

sediment and depend further on the properties of the

benthic communities.

In recent years, several numerical sediment trans-

port models have been presented (e.g. Holt and James,

1999; Ribbe and Holloway, 2001; Jankowski et al.,

1996; Black and Vincent, 2001; Puls et al., 1994;

Gerritsen et al., 2001; Lou and Ridd, 1997; Lou et

al., 2000) using either the quasi-Lagrangian or Eulerian

treatment. In the quasi-Lagrangian approach, the sed-

imentary material is represented by a large number of

test particles, whose trajectories are computed in an

Eulerian velocity field provided by a circulation model

(e.g. Black and Vincent, 2001; Puls et al., 1994). In this

case, the spreading of the test particles, which represent

the sedimentary material, is virtually independent of

the grid spacing of the underlying hydrodynamical

model. Only the spatial resolution of the driving

currents is restricted by the model grid. However, this

approach can fail at low numbers of test particles,

which may move in completely different ways causing

unrealistic fluctuations.

In the Eulerian approach (e.g. Holt and James,

1999; Ribbe and Holloway, 2001; Jankowski et al.,

1996), a transport equation is solved for the sediment

concentration. This allows proper simulations also at

low concentrations, but the resolution of the concen-

tration gradients is affected by the grid spacing. The

present study is based on an Eulerian approach where

the moving sedimentary material is treated as a tracer

variable in the circulation model.

Two broad classes of problems may be distin-

guished. One class aims at the evolution of the seabed

and distribution of sediments over long time scales—

e.g. computing the present seafloor as a result of

processes acting for several hundred years on an

initial distribution. The other, less ambitious aim is

to compute scenarios how sedimentary material is

transported in response to wind forcing or tides over

smaller time scales, say weeks to months. An ade-

quate understanding and modeling of these transport

processes is important for many applications, such as

estimations of the impact of dumping and dredging to

a marine system.

In this paper, we consider the second type of

problem. We study the transport of sedimentary ma-

terial in the western Baltic Sea with the help of a

model system, which links a general ocean circulation

model, a wave model, a BBL model and a sediment

transport model. Important information needed for the

model simulations is a consistent data set of the

natural sediment distribution prescribed by observed

data and appropriately gridded to match the model

resolution. At time scales of a few weeks to a few

months, changes of the sediment properties of the

seafloor are small and are ignored in our approach.

The paper is mainly a model study of the physical

processes but with relevance for biogeochemical

applications. The main goals are:

� to establish the spatial distribution patterns of

bottom shear stresses in response to different wind

forcing,� to identify the transport paths and deposition areas

of different materials under varying hydrographic

conditions.

The paper is organized as follows. Section 2 gives a

brief outline of the model system. In Section 3, the

bottom shear stress distribution in the western and

central Baltic and the transport of sedimentary material

is studied in a series of model experiments. Since in the

shallow areas of the Baltic the role of waves and, in

particular, the wave-induced bottom shear stress is

important, we commence our study with idealized

constant wind forcing in Section 3.1. The bottom shear

stress distribution is discussed for different wind direc-

tions which imply substantial changes of the fetch. In

Section 3.2 the model simulations are driven by a

realistic wind forcing for the year 1993, which was

selected because of the occurrences of extremely strong

wind events. Transport patterns of fine material and

potential erosion areas are discussed for several time

periods with different forcing conditions. Moreover,

C. Kuhrts et al. / Journal of Marine Systems 52 (2004) 167–190 169

response experiments with horizontal homogeneous

initial distributions of fine material, which may corre-

spond to fluffy layers or dormant stages of plankton

cells, are carried out to identify accumulation areas and

the associated time scales. Finally, a summary, con-

clusions and an outlook are given in Section 4.

2. The model system

The study is based on a numerical model system

which consists of four coupled components: a three-

dimensional circulation model, a wave model, a

bottom boundary layer model and a sediment trans-

port model. The model components are briefly out-

lined in the following.

2.1. The circulation model

The evolution of currents, temperature and salinity

in response to atmospheric forcing and river dis-

charges is calculated with a circulation model based

on the Modular Ocean Model, MOM-3.1 (Pacanowski

and Griffies, 2000). We use an implementation with

an explicit free surface scheme, which involves tracer

conservation properties as described in Griffies et al.

Fig. 1. Topographic map of the Baltic Sea. For later reference, specific are

(Mecklenburg Bight), K (Kadet Channel), D (Darss Sill), R (Rønne Bank

(2001). The model covers the whole Baltic Sea and

has an open boundary to the North Sea. The model

topography is based on a digitized map of the Baltic

Sea compiled by Seifert et al. (2001) which is shown

in Fig. 1 for the western and central Baltic together

with the geographical names used for later reference.

The horizontal model resolution in the western and

central Baltic is 3 nautical miles. The vertical resolu-

tion is 3 m in the upper water column down to 90 m

and is then stretched to 6-m intervals. To improve the

representation of the topography, the bottommost cells

are adjusted to the topography and can have partial

heights with a minimum cell thickness of 1 m. The

horizontal velocity components and sea level eleva-

tion are prognostic variables, while the vertical veloc-

ity is diagnosed from the divergence of the horizontal

flow. The pressure is calculated from the density

distribution. The UNESCO equation of state is used

to calculate the densities from temperature and salin-

ity. The time steps are 150 s for baroclinic currents

and tracers and 15 s for the barotropic mode.

Horizontal subgrid processes are parameterized by

the Smagorinsky scheme (Smagorinsky, 1993), where

the horizontal eddy viscosity is related to the defor-

mation rate of the flow field. For the vertical subgrid

mixing, the kpp-mixing scheme is used (Large et al.,

as are indicated by letters: F (Fehmarn Belt), L (Lubeck Bight), M

), O (Oder Bank) and P (Pomeranian Bight).

Table 1

Choice of parameters for the Smagorinsky and Pacanowski–

Philander subgrid parameterization

Background horizontal viscosity A0m 106 cm2 s� 1

Background horizontal diffusivity A0t 105 cm2 s� 1

Background vertical viscosity j0m 1.0 cm2 s� 1

Background vertical diffusivity j0t 0.1 cm2 s� 1

Prandl number 10

Scale factor 3

Maximum diffusivity jmaxt 10 cm2 s� 1

Vertical viscosity scale jmaxu 10 cm2 s� 1

Wind mixing (uppermost layers) ju jmaxu


1994). In the two uppermost layers, a constant vis-

cosity is prescribed to simulate wind-induced mixing.

The parameters were chosen as small as possible, but

large enough to maintain numerical stability of the

model. The numerical values of the chosen parameters

are listed in Table 1.

2.2. The wave model

For the simulation of the wave field, we have

adopted the model of Donelan and Schwab which is

described in Schwab et al. (1984) and Liu et al.

(2001). This model is based on the wave momen-

tum balance equation and employs the so-called

JONSWAP form (Hasselmann et al., 1973) of the

frequency spectrum. The prognostic variable of the

model is the wave momentum. The wave parame-

ters, peak frequency and significant wave height are

calculated from the wave momentum in response to

the wind.

Fig. 2. Schematic diagram of the boundary layer mod

To take finite depth effects into account, we use the

Texel–Marsen–Arsloe (TMA) spectrum (Bouws et

al., 1985), which provides an extension of the deep-

water JONSWAP spectrum to waves in shallow water.

For the transformation of the JONSWAP spectrum into

the corresponding TMA spectrum, the Kitaigorodskii

scaling law is applied (Kitaigorodskii et al., 1975).

The computed peak frequencies (or equivalently,

wave numbers) and significant wave heights provide

input data for a wave-current bottom component of

the BBL model.

2.3. The bottom boundary layer model

A key quantity governing the transport of sedimen-

tary material is the shear stress on the seabed, which is

generated by currents and waves within the BBL. The

bottom-near boundary layer is expected to be thin (less

than 30 cm) and not resolved in the circulation model.

Even the treatment of partial cells implies that in the

hydrodynamical model, the distance between the low-

est velocity point and the bottom is on the order of

0.5–1.5 m. Therefore, a specific boundary layer model

component has been introduced, which involves the

interaction of currents, waves and seabed properties.

We use an analytical model to calculate the current-

induced bottom shear stress from the lowermost ve-

locity point in the circulation model. A schematic

diagram of our boundary layer model is given in Fig. 2.

Waves enhance the near-bed turbulence and in-

crease the effective bottom roughness acting on the

current. To consider this effect, we apply the concept

el, with piecewise logarithmic velocity profiles.


of Grant and Madsen (1979). This approach assumes

the existence of a wave boundary layer of thickness

dW= 2ju*cw/x, with j = 0.4 being the Karman con-

stant, x is the wave frequency and u*cw ¼ffiffiffiffiffiffiffiffiffiffiffiffiscw=q

p¼ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi

u2*c

þ u2*w

qis the total bottom shear velocity caused

by currents and waves. Assuming a vertically constant

shear stress, a piecewise logarithmic velocity profile

can be constructed:

z < dW : ucðzÞ ¼u*cj

u*cu*cw

� �ln30z

kb;

z > dW : ucðzÞ ¼u*cj

ln30z

kbc; ð1Þ

where z is the height above the seabed, kb denotes the

geometrical bottom roughness and kbc is the apparent

bottom roughness caused by the turbulence in the

wave boundary layer. Both profiles are matched at

the height z= dW, implying the relationship

kbc ¼ kb24u*cwxkb

� �b

; b ¼ 1�u*cu*cw

: ð2Þ

For calculation of the wave shear velocity u*w,

which is assumed to be not affected by the current, we

use the parameterizations of Nielsen (1992a):

u2*w ¼ 1

2fwU

2M;

fw ¼ minfexp½5:5 kb

A

� �0:2

�6:3; 0:3g: ð3Þ

Here UM=(pH/T)[sinh(kh)]� 1 is the maximal horizon-

tal velocity for a wave of height H at the water depth

h and A=(H/2)[sinh(kh)]� 1 is the amplitude of the

wave oscillation on the bottom (k denotes here the

wave number).

To compute the current bottom shear velocity u*cfrom the lowest velocity point of the model grid uc(z),

we start with an initial guess for the apparent bottom

roughness kbc according to Eq. (1) and solve then the

Eqs. (1) and (2) iteratively.

The total bed shear stress consists of two compo-

nents: skin friction shear stress, corresponding to the

force acting on the individual grains, and form drag,

which is generated by larger structures of the seabed.

The skin friction shear stress controlling resuspension,

bed load transport and deposition is the relevant

component for the sediment transport. To extract this

quantity from the total current shear stress, the bound-

ary layer model needs further refinement.

Following the work of Smith and McLean (1977),

we introduce an additional friction sublayer of height

zm, where the velocity profile is related to the local skin

friction velocity (see Fig. 2). The roughness parameter

in this sublayer is the grain roughness kbd, and the

following logarithmic velocity profile is adopted

z < zm : ucðzÞ ¼u*scj

ln30z

kbd: ð4Þ

For a bed structure dominated by ripples or

dunes, the thickness of the sublayer is set to zm=

0.003kbd(30E/kbd)0.8 (Smith and McLean, 1977),

where k is the wavelength of ripples or dunes.

Matching the velocity profile at the top of the skin

friction sublayer, given in Eq. (4), with the velocity

profile at the lower border of the wave boundary

layer, given by Eq. (1), at z = zm leads to the follow-

ing expression for the current skin friction velocity

u*sc ¼u2*c

u*cw

ln30zm

kb

ln30zm

kbd

: ð5Þ

The total skin friction velocity u*s consists of the

contribution of currents and waves,

u*s ¼ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiu2*sc

þ u2*sw

q: ð6Þ

To estimate the wave skin friction shear velocity,

u*sw, we apply a relation corresponding to Eq. (3)

u2*sw ¼ 1

2fswU

2M;

fsw ¼ minfexp½5:5 kbd

A

� �0:2

�6:3; 0:3g; ð7Þ

where the grain roughness kbd is used.

Next, we have to quantify the bed roughness pa-

rameter kb, which is required to determine the bed shear

velocities u*c and u*w. Generally, the bed roughness can

be divided into three parts (Xu and Wright, 1995): the

grain roughness kbd, the form drag roughness kbr, and

the roughness generated by near-bed sediment trans-

port. Neglecting the latter contribution yields

kbckbd þ kbr: ð8Þ

Table 2

Sediment types and parameters which were used to describe the

mean properties of the seabed

Sediment type d50 (Am) kbd (cm) kbr (cm)

Silt 20 0.005 0.18

Fine sand 130 0.033 1.17

Medium sand 250 0.063 2.25

Hard-rock – 0.125 4.50


For the grain roughness, the common approxima-

tion kbd = 2.5d50 is chosen, which relates the rough-

ness parameter to the mean grain size d50. The

quantity kbr depends on the actual bed geometry,

i.e. ripples or biological benthic structures. Under

the assumption that ripples dominate the structure of

the seabed, the bed roughness kbr can be character-

ized by ripple spacing and ripple height, k and g.Using a relation proposed by Nielsen (1983), we

have kbr = 8g(g/k). The bed geometry is subject to

changes due to waves and currents as well as

biological activity. In the present study, we ignore

such variations and characterize the mean state of

the seabed by fixed values of k and g. For the ripple

spacing, we adopt a parameterization suggested by

Yalin (1977), kg1000d50, and for the ripple steep-

ness, we assume g/k = 0.1.The data of the bottom topography of the Baltic

Sea have to be complemented by information of the

sedimentary characteristics of the seabed. We assign

to each bottom model box a representative sediment

type, which corresponds to the mean sediment prop-

erties of the seabed in that area. This amounts to a

Fig. 3. The distribution of the sedim

smoothed representation of the seabed because spatial

variations cannot be fully resolved by grid models.

We have chosen four representative sediment types

distinguished by mean grain size, d50, and bed rough-

ness, kbr, to describe the seabed of the Baltic Sea

model. The resulting sediment distribution is shown in

Fig. 3, (Bobertz, personal communication), and the

numerical values of the sediment parameters are listed

in Table 2.

2.4. The sediment transport model

In the previous subsections, a method was provid-

ed to compute the skin friction velocity u*s within our

ent types used in the model.

Table 3

Material parameters of the considered sedimentary material

Sediment wsink

(cm/s)

u*r(cm/s)

u*d(cm/s)

u*b(cm/s)

M

(s/cm)

SPM 4 10� 4 2.0 1.0 – 2.0 10� 5

Fine sand 4 10� 1 1.4 1.4 1.1 1.0 10� 5

Fluffy layer 1 10� 1 0.5 0.5 – 2.0 10� 5

Cysts 1 10� 2 0.5 0.5 – 2.0 10� 5


model system, which is needed to control the resus-

pension, transport and settling of the sedimentary

material. First we look at the transport of sedimentary

material in suspension, which is governed by a so-

called tracer equation

Bc

Btþ!jðc � !u Þ þ B

Bzðc � wsinkÞ ¼

!jðm!jcÞ; ð9Þ

where c is the concentration of the suspended sedi-

mentary material,!u the full 3D current velocity, wsink

the settling velocity (negative downward) of the

considered sediment type and m is the eddy diffusivity.

Deposition or resuspension processes are taken into

account by the bottom boundary condition

c � wsink � mzBc

Bz

� �bottom

¼ Q; ð10Þ

where Q is a source term describing the quantity of

sediment per unit area which is resuspended or

deposited at the bottom. The source term Q depends

on the total skin friction velocity u*s and specific

material constants

Q ¼

ðwsink � cÞbottom; u*sVu*d

0; u*d < u*sVu*r:

qr; u*s > u*r

8>>>><>>>>:

ð11Þ

Here, u*r is the critical shear velocity for resuspension

and u*d is the critical shear velocity for deposition. If

the skin friction velocity falls below the critical value

for deposition, material sinks to the bottom with its

characteristic settling velocity. If the skin friction

velocity exceeds the critical value of resuspension,

the material is brought into suspension at a rate qr.

Following Puls and Sundermann (1990), we parame-

terize the erosion rate qr as

qr ¼ Mqðu2*s � u2*rÞ; u*s > u*r; ð12Þ

where q is the density of water and M is a constant,

which depends on the considered material (see

Table 3.

The material deposited at the seabed per unit

bottom area is described by the concentration CA,

which changes dynamically due to bed load transport,

deposition and resuspension

BCA

Btþ!

j!qb ¼ �Q: ð13Þ

The coupling between sediment in suspension and

deposited material at the bottom is given by the source

term Q appearing already in Eq. (10). The direction of

the bottom transport flux!qb coincides with that of the

bottom-near velocity. To quantify the bed load trans-

ports of sand, we apply the parameterization proposed

by Meyer-Peter and Muller (1948),

qb ¼ qs

ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiðs� 1Þgd350

q 4u2*s

ðs� 1Þgd50� 0:188

!3=2

;

u*s > u*b; ð14Þwhere u*b is the critical velocity for bed load transport,

s is the relative density of the sediment, qs is the

sediment density and g is the gravitational acceleration.

We solve the differential equations (9) and (13) for the

transport processes with an upstream finite differences

scheme. This scheme is fast, but it is also known to be

diffusive. We have conducted several comparisons

with a flux-corrected scheme, and it turned out that

the general transport patterns are similar.

In the model simulations described in the following

section, we study the transport of three different types

of sediment: suspended particulate matter (SPM), fine

sand and fine biogenic material, which may refer to

fluffy layers or dormant stages (cysts). Processes such

as aggregation and consolidation, changing the mate-

rial parameters of the sediments, are not taken into

account in the present paper.

3. Model simulations

After the detailed description of the model system

in the previous section, we will now apply the model.


One of the key quantities in modeling sediment

transport is the bottom shear stress induced by waves

and currents. With our model system, we can estimate

the bottom shear stress distribution in the western and

central Baltic under different forcing conditions. This

allows the identification of regions of high and low

bottom shear stress that are potential sites for resus-

pension and deposition, respectively. Furthermore, we

wish to explore the natural transport pathways of

different sedimentary materials in parts of the Baltic

under varying hydrographic conditions.

In a tideless sea like the Baltic, the bottom currents

are relatively weak and, therefore, waves play an

important role for the transport process by stirring

up deposited material from the seabed. The circulation

in the Baltic is highly variable due to changing

weather patterns in temperate latitudes. In particular,

in the western Baltic, which is part of the transition

area between Baltic and North Sea, currents with

strong vertical and horizontal gradients develop in

response to far field forcing (pressure gradient due to

sea level differences between the Baltic and the

Kattegat) and local forcing due to the local winds

(see Fennel and Sturm, 1992; Schmidt et al., 1998).

In this section, the following types of model

experiments are considered. First, we study the influ-

ence of the wind fetch on the bottom shear stress

distribution in the western Baltic. For the model year

1993 with several strong wind episodes in the Baltic,

maximum shear velocities are calculated. Further, we

discuss the transport patterns of different types of

sedimentary material in the western Baltic. A last set

of experiments is devoted to the transport of fluffy

layer material.

3.1. Simulations with idealized winds

The Baltic is characterized by neglectable tides and

extended shallow areas where the bottom shear stress

is dominated by waves. Because of the nearby coasts,

the wind fetch strongly depends on the wind direction.

In order to visualize the important role of the fetch, we

start our series of simulations with constant winds of

15 m/s from different directions. We consider in

particular the cases of southwest, west, north and

northeast winds. Events of strong winds from these

directions are frequently observed, except northern

winds, which occur only episodically.

All experiments start with the same initial con-

ditions of sea level and stratification. The model is

initialized with monitoring data of the Baltic Sea

Research Institute (IOW) for the western and central

part of the Baltic for January completed by climato-

logical data of Janssen et al. (1999) for the remaining

areas. The initial sea level gradients have been

adjusted to the horizontal salinity gradients. The

model topography is shown in Fig. 1. After a spin-

up phase of several model days, the currents and

waves are adjusted to the forcing. The flow patterns

can roughly be characterized by Ekman transports in

the surface layer, Ekman recirculation below the

surface and topographically guided flows trapped at

the slopes (not shown). The quasi-steady states are

used to study the effects of waves on the near-bottom

shear stress.

We confine the discussion on the simulated skin

friction velocities, which are calculated according to

Eq. (6) and the related formulas described in Section

2.3. The results are shown in Figs. 4 and 5 for the

different wind directions. The contributions of the

currents to the skin friction velocities are relative

small and do not exceed a maximum value of 0.2

cm/s. Therefore, the shear velocities display the role

of the waves. The magnitude of wave-generated shear

velocity decreases significantly with increasing depth

and, consequently, high shear velocities are found in

shallower areas. Although maps of the wave fields are

not shown, the fetch effect is clearly visible in Figs. 4

and 5 through the shear velocity distribution in

response to different wind cases. In particular, for

north and northeastern winds, we find maximum

values of the shear velocities of about 3.5 cm/s

distributed over a wide range. The strongest wave

effect is found for northeastern wind where the fetch

is at its maximum. For southwestern wind, we find

high friction velocities in the shallow areas of the

central Baltic, but relatively small signals in the

western Baltic and near the southern coast. West wind

generates friction velocities which are generally

smaller than in the other cases.

Since the wave field adapts with a time scale of a

few hours to a change in the wind direction and wind

speeds of 15 m/s are typical for strong wind events in

the Baltic area, the constant wind experiments provide

reasonable, fetch-dependent shear velocities in re-

sponse to strong wind events.

d forcing from north (upper panel) and northeast (lower panel).


3.2. Simulations of the model year 1993

Owing to the dominant role of the waves, the

idealized wind studies give already some clues on

potential areas of erosion and deposition. However,

to simulate transport routes and distribution pat-

Fig. 4. Skin friction velocities resulting from constant win

terns of sedimentary material in response to wind

and waves requires realistic forcing scenarios. Be-

cause of the occurrence of strong wind events in

January and February 1993, we have chosen this

year for our calculation. A time series of the wind

at the position (12j42VE, 54j42VN) is shown in

Fig. 5. Skin friction velocities resulting from constant wind forcing from west (upper panel) and southwest (lower panel).


Fig. 11. We have conducted annual runs including

time-slice experiments, where the transports of

sedimentary material are studied over a certain

period of time.

3.2.1. Potential areas of erosion and deposition

To identify potential areas of erosion and deposi-

tion, we analyze the calculated shear velocities for the

model year 1993. For every grid point, the local


maximum of the daily mean shear velocity, shown in

Fig. 6 (upper panel), was estimated. Most of these

maximum values are reached during the strong wind

periods in January and February 1993. For an apprais-

al how strong the maximum shear velocities are

Fig. 6. Maximum of the daily means of the skin friction shear velocity for e

the hourly means of the skin friction shear velocities in the period of Jan

reduced due to the averaging over 1 day, we computed

also the absolute maxima of hourly values (see Fig. 6,

lower panel). The comparison of hourly and daily

mean values shows similar patterns but slightly re-

duced magnitudes for the daily means. This indicates

very grid cell in the model year 1993 (upper panel), and maximum of

uary and February 1993 (lower panel).

Table 4

Critical shear velocities for erosion of the sediment types considered

in the model

Sediment type Crit. erosion

shear vel. (cm/s)

Silt 4.0

Fine sand 1.2

Medium sand 1.5

Hard-rock –


that the strong events have a duration of less than 24

h. This can directly be seen from the time series of

the wind in Fig. 11. Moreover, the maximum wind

speeds exceeded the value of 15 m/s applied in the

idealized experiments. For this reason, the maximum

shear velocities displayed in Fig. 6 reach higher

values as those shown in Fig. 5, although the strong

winds in the wintertime of 1993 come from westerly

directions.

The maximum shear velocities calculated for the

year 1993 can be used to identify potential areas for

erosion and resuspension. To this end, we define the

‘erosion risk’ by max(0, (u*s2� u*crit

2)), which is pro-

portional to the difference of the shear stresses gen-

erated by currents and waves and the critical shear

Fig. 7. Potential erosion areas where the maximum skin friction u*smax2

sediment type (see Fig. 3).

stress for erosion that is a property of the seabed. The

critical shear velocities, u*crit, for the model sediment

types characterizing the seabed are given in Table 4.

The critical erosion shear velocities for the sandy

sediments of the Mecklenburg Bight were measured

by Bohling (2002, 2003). For the silt, we adopt a

minimal value of 4.0 cm/s as suggested in the standard

literature (e.g. Tolhurst et al., 2000; Austen et al.,

1999; Amos et al., 1997). By comparison of the

maximum shear velocities, shown in Fig. 6 (upper

panel), with the critical values for erosion, a map of

the erosion risk can be generated as shown in Fig. 7.

Our findings indicate a high erosion risk in several

areas: south off the Danish islands, on the Rønne

Bank, on the Oder Bank as well as southeast off the

Darss Sill.

These results are in agreement with observed

morphodynamic processes. In the coastal areas south-

west and southeast off the Darss Sill, erosion and

transport of sand are detected regularly resulting in

changes of the shoreline (see, e.g. Tiepolt and Schu-

macher, 1999). The Oder Bank is considered to be an

important source for coarse-grained sediment supply

in the Pomeranian Bight (Schwarzer et al., 2003).

Future model calculations with substantially increased

exceeds the critical shear u*crit2 for resuspension of the underlying


horizontal resolution could help to study the transport

paths and transport rates in more detail.

An important component of the material fluxes from

shallower to deeper areas in the Baltic are thin layers of

easily erodible material which are found at calm con-

ditions almost everywhere on the seabed. The material

within these so-called fluffy layers has a high organic

content and can consolidate to mud. The critical shear

velocity for the resuspension of fluffy layers is only

about 0.5 cm/s (Christiansen et al., 2002). As shown in

Fig. 8, the areas where the calculated skin friction

velocities in 1993 do not exceed a value of 0.5 cm/s

are the western edges of the Lubeck Bight and the

Arkona Basin, the Bornholm Basin, the Stolpe Chan-

nel, the Gdansk Bight and the Gotland Depression.

These regions are potential areas for the accumulation

of nutrients and pollutants transported within fluffy

layers. Our result is in accordance with the observed

distribution of mud and silt as shown, for example, in

the sediment map of Nielsen (1992b), which is based

on a large amount of geological surveys.

3.2.2. Spreading of material from point sources

The model can also be used to investigate the

development of plumes of sedimentary material added

Fig. 8. Potential deposition areas for fluffy material where the skin frictio

resuspension.

to the system. Such kind of model experiments have a

great importance for environmental assessments with

regard to dumping of material on the seabed or to

quantify fluxes of material stirred up by dredging

activities.

In this subsection, we will show how different

types of material are distributed in the western Baltic

and how the transport rates vary between different

seasons. We study the transport patterns of two types

of material: suspended particulate matter (SPM) and

fine sand. The settling velocity of SPM depends in

general on the aggregation size, which is a function of

the suspended sediment concentration, the turbulent

shear stress and other quantities. In our model experi-

ments, we want to investigate the maximum range of

turbidity plumes. We use a constant value of 4 10� 4

cm/s for the settling velocity representing a lower

bound for this parameter (van Wijngaarden and Rob-

erti, 2002). Data of critical shear velocities for fine-

grained material vary over wide ranges (see, e.g.

Winterwerp, 1989). We have chosen a critical shear

velocity for resuspension of 2.0 cm/s and for deposi-

tion of 1.0 cm/s. For the erosion constant M, a value

of 2.0 10� 5 s/cm is used according to measure-

ments of Bohling (2003). Assuming a mean grain

n velocity u*smax does not exceed the critical value of 0.5 cm/s for


diameter of 100 Am for the fine sand, a sinking

velocity of 4 10� 1 cm/s, a critical shear velocity

for resuspension and deposition of 1.4 cm/s and a

critical shear velocity for bed load transport of 1.1 cm/

s are calculated using parameterizations proposed by

Zanke (1982). To characterize the erosion constant for

transport in suspension, we use a value M = 1 10� 5

s/cm. The parameters are summarized in Table 3. We

Fig. 9. The vertically integrated concentration of fine sand in g/cm2 at the

base 10. At the two sources, indicated by asterisks, a sediment concentrat

beginning of each period.

consider two artificial sediment sources, one located

in the southern Mecklenburg Bight and the other one

in the Pomeranian Bight. The source locations are

indicated by asterisks in Figs. 9 and 10. At both

sources, 3 104 tons of suspended sedimentary ma-

terial are inserted into the bottommost model box at

the beginning of each time-slice experiment. The

simulations, which can be assumed to mimic idealized

end of the biweekly model periods, plotted on logarithmic scale to

ion of 0.1 g/cm2 was initialized in the bottommost model box at the


dumping or dredging events, describe spreading of

sedimentary material over biweekly periods under

different forcing conditions of the year 1993.

Simulated distribution patterns of the vertically

integrated concentrations are shown in Figs. 9 and

10 for four winter and two summer situations in 1993.

In these figures, a logarithmic scale is used to display

a wide range of the concentrations.

Fig. 10. The vertically integrated concentration of SPM in g/cm2 at the end

two sources, indicated by asterisks, a sediment concentration of 0.1 g/cm2 w

period.

A significant transport of fine sand is found only

for the two stormy periods, (14.01.–28.01.) and

(29.01.–12.02.), in wintertime. The sand from the

source in the Mecklenburg Bight is transported in

both cases to the northeast and partly deposited in the

Kadet Channel. In the Pomeranian Bay, most of the

material was deposited near the source; only during

the period (14.01.–28.01.) a substantial amount of

of the biweekly model periods, plotted on logarithmic scale. At the

as initialized in the bottommost model box at the beginning of each

C. Kuhrts et al. / Journal of Marin182

sand was moved eastward. Our calculations show that

most of the sand is transported near the seabottom,

and therefore the transport paths are prescribed by the

bottom currents.

Contrary to the sand, the model SPM spreads over

significantly larger areas. Due to the small settling

velocity, the SPM stays longer in suspension and can

be mixed over the whole water column. Due to the

strong horizontal and vertical current gradients in the

western Baltic, the spreading of SPM is supported by

different current directions at different parts of the

water column. Nevertheless, in all cases, substantial

amounts of the SPM are also deposited near the

sources. In the Pomeranian Bight, where the vertical

gradients of the flow are much weaker, the transport

of SPM is mainly guided by the topography to the

northwest and northeast along the Oder Bank. Con-

sidering the source in the Mecklenburg Bight, we find

strong seasonal differences in the transport directions

and rates. During the two periods (14.01.–28.01.) and

(29.01.–12.02.), the transport is directed to the north-

east and southwest, while in the periods (29.01.–

12.02.) and (13.02.–27.02.), the material was trans-

ported towards northwest into the Fehmarn Belt. In

the summer periods (13.06.–27.06.) and (28.06.–

12.07.), the transport is mainly westward and guided

by the topography. The transport rates during the

summer periods are significantly smaller. The differ-

ent ranges of the spreading areas in summer and

winter can be explained by the differences in the wind

forcing (see Fig. 11). During summer, the winds are

relatively weak, implying smaller current speeds and

low wave action. The thermal stratification in summer

(see, e.g. Fennel and Sturm, 1992) prevents a mixing

through the thermocline. Hence, the typical vertical

current shear between the surface layer and the water

below does not contribute to the effective diffusivity.

In wintertime, the wind forcing is stronger and the

spreading is enhanced by the vertical current shear

which, combined with the strong vertical mixing,

increases the effective diffusivity.

Summarizing, we find that in the western Baltic,

transport of sedimentary material over longer distan-

ces occurs only under extreme wind events. The

transport paths of SPM and fine sand differ strongly

as a result of the different settling velocities. During

summer conditions, the transport rates are generally

smaller.

3.2.3. Deposition of homogeneously distributed

material

In the last set of experiments, we consider a

different type of experiments which can help to

understand the transport of fine material in relation

to two important applications: (i) the accumulation of

easily erodible fluffy layers and (ii) the spreading of

dormant stages (cysts), which may be formed in the

upper layer and sink down to the bottom in a couple

of days. Here we will not go into the details of

formation and biogeochemical properties of fluffy

layers and also not discuss the formation of dormant

stages in the life cycle of phytoplankton. The question

we are interested in is how this kind of material is

redistributed under the influence of waves and cur-

rents. Nutrients and pollutants delivered by river

discharges are expected to be bound to organic flocks,

which are forming fluffy layers near the bottom.

Hence, the deposition areas of these constituents are

the regions where the fluff eventually accumulates at

the seabed. Accumulation areas of cysts are of interest

because they may be seed regions where blooms may

commence. In particular, this can be of importance for

the prediction of harmful algal blooms.

The deep basins are known to be the potential areas

for deposition and consolidation of fine material

(Emeis et al., 2000). The remaining question is at

which paths the material is transported from the

shallower areas into the deep basins for different

forcing situations. To encounter this question, we

perform response studies starting with a homogeneous

initial distribution of very fine material evenly spread

in a near-bottom fluffy layer or in the surface layer as

cysts. We have chosen the four time slices (A)–(D) of

the model year 1993, listed in Table 5. In Fig. 11, a

time series of the wind is shown at the position

(12j42VE, 54j42VN) for the considered time slices.

The distribution of fine material is reinitialized at the

beginning of each experiment. Critical shear velocities

for deposition and resuspension of fluffy layers (e.g.

cysts) are characterized by a value of 0.5 cm/s that was

measured from sediment probes of the western Baltic

(Ziervogel and Bohling, 2003). For the erosion con-

stant, M, introduced in Eq. (12), the value of

2.0 10� 5 s/cm is used according to measurements

of Bohling (2003). For the cysts, we assume a settling

velocity of 0.1 cm/s. The settling velocity of the fluffy

layer material depends strongly on the size of the

e Systems 52 (2004) 167–190

Table 5

Time slices (A)– (D) over which the distribution patterns of

fluffy layer were calculated

Case Period

A 1 January–13 February 1993

B 15 March–28 April 1993

C 13 June–27 July 1993

D 27 August–10 October 1993

Fig. 11. Wind speeds (solid lines) and directions (dotted lines) at position (12j42VE, 54j42VN) for the four periods (A)– (D), which were selectedfor the time-slice experiments.


aggregates. The amount of fine material bound in

aggregates with a flock size larger than 50 Am shows

a strong seasonal variability (see Christiansen et al.,

2002). Therefore, we can expect a seasonal variation of

the settling velocities leading to much lower sinking

rates for suspended matter in autumn and winter than in

spring and summer. For our model calculations, we

have chosen different values of the settling velocity

(0.001–0.1 cm/s) of fluffy layers. In order to highlight

the influence of the different forcing conditions, we

compare time-slice experiments with the same settling

velocity neglecting the seasonal variation of this pa-

rameter. Additionally, we show the effect of different

settling velocities on the distribution patterns consid-

ering as example the winter period.

Fig. 12. Vertically integrated concentration of fluffy layer material at the end of the time-slice experiments for period (A) (upper panel) and

period (B) (lower panel). The model was initialized with a homogeneous concentration of 0.1 g/cm2 at the seabed.



The simulations showed that the spreadings of the

fluff and the model cysts differ only slightly as a result

of the different settling velocities. Thus, the differ-

Fig. 13. Vertically integrated concentration of fluffy layer material at the

period (D) (lower panel). The model was initialized with a homogeneous

ences due to the different initial distribution, cysts in

the surface layer and fluff in the bottom layer are

negligible. This can be understood by the fact that

end of the time-slice experiments for period (C) (upper panel) and

concentration of 0.1 g/cm2 at the seabed.

Fig. 14. Vertically integrated concentration of fluffy layer material at the end of the time-slice experiment (A) with settling velocities of 10� 2

cm/s (upper panel) and 10� 3 cm/s (lower panel) used in the calculation.



even for low settling speeds of 0.01 cm/s, the material

reaches the bottom after a few days. Since the areas of

accumulation are virtually the same for both cases, we

will give only the results for the fluff.

The resulting distributions at the end of the time

slices are shown in Figs. 12 and 13 for the western and

central Baltic. During the first time-slice experiment

(A), several storms have passed the Baltic. Owing to

the strong wind events, the material in the shallower

areas is brought into suspension and advected by the

currents. Because of the long period of strong winds,

the material can settle only in the deeper parts of the

Baltic (see Fig. 12, upper panel). The highest concen-

trations of accumulated material occur in the slope

regions of the deep areas. As a result of decreasing

near-bottom turbulence, suspended material from the

shallower areas settles and the influence of waves is

too weak to resuspend the deposited material. Signif-

icant accumulations develop at the southwestern

slopes of the Arkona Sea, the Bornholm Sea, the

Gdansk Bight and in the Nemunas Channel.

For the period (B), a considerable transport of

material occurred only during the first days with wind

speeds up to 18 m/s in the western Baltic. In the

remaining period, there was virtually no resuspension.

The resulting distribution of material is shown in Fig.

12 (lower panel). Material accumulated at the south-

western slope of the Bornholm Sea and also in parts of

the Pomeranian Bight and the Kadet Channel. Appar-

ently, more material was retained in the shallower areas

compared with period (A). We consider period (B) as a

typical winter situation with considerable transport in

several shallow parts of the Baltic, while period (A)

represents a phase of extremely strong transports in all

regions, where the fine material has been removed from

the areas with a water depth up to 30 m.

For the test experiments (C) and (D), we have

chosen periods in summer and early autumn where

strong wind events with maximum wind speeds of 15

m/s occurred. The duration of these events was

limited to 1 or 2 days. We find a substantial amount

of material remaining on the Middle Banks and the

Hoburgs Bank (see Fig. 13), while nearly all material

was removed during the winter periods (A) and (B).

Only the Oder Bank and the Rønne Bank are affected

where a large amount of material was removed.

Obviously, the transport of fine material is weak

during the summer and early autumn. As a rule of

thumb, it follows that transport of fine material starts

in the shallow regions when the wind speed exceeds a

value of 10 m/s.

Although the strong currents, such as coastal jets,

are guided by the topography, there are also cross

slope flows, in particular Ekman transports in the

upper layer and recirculation below, which provide

fluxes into the central basins. Resuspended material in

the shallow areas can be moved back and forth until it

reaches deeper part and sinks to depths where it

cannot again be resuspended by waves.

In the first set of simulations discussed above, the

settling velocity was 0.1 cm/s implying a high degree

of aggregation of the fluffy layer material. In spring

and summer, most of the material aggregates to larger

flocks, whereas in autumn and winter, only 10% of

suspended material is aggregated (Christiansen et al.,

2002). Therefore, we repeated the calculations for

period (A) with smaller settling velocities of 0.01

and 0.001 cm/s. The results, shown in Fig. 14,

indicate that with decreasing settling velocity, more

material is transported into the centers of the deep

basins. However, even for the smallest settling veloc-

ity of 0.001 cm/s, relative high accumulation of

material is found in the slope regions of the Arkona

Basin, the Bornholm Basin and in the Nemunas

Channel.

4. Summary, conclusions and outlook

With the aid of the model system presented in

Section 2, we have studied basic characteristics of the

transport of sedimentary material in the western Baltic

Sea. The results of the series of model experiments

described and discussed in Section 3 can be summa-

rized as follows:

� The bottom shear stress in the tideless Baltic is

dominated by the wave contribution in the

shallower areas. Maximum skin friction velocities

of about 3.5 cm/s occur in regions with large wind

fetch as, for example, the Oder Bank.� The spreading of SPM and fine sand from two

point sources shows seasonal and regional

differences:

– Suspended particulate matter can be transported

over the whole water column. Owing to the


vertical gradients of the currents, SPM spreads

over wide areas in the Mecklenburg Bight, while

in the Pomeranian Bight, the plumes are more

confined and governed by topographically

guided currents.

– A remarkable transport of fine sand occurs only

for wind speed above 15 m/s. The transport path

is mainly prescribed by the bottom-near current

directions.

– The amount of transported material is much

lower during summer because of weaker winds.� Fine material, which may refer to fluff or cysts, is

rapidly eroded from shallow regions if the wind

speed exceeds 10 m/s. The material tends to

accumulate at the slopes of the adjacent basins

below approximately 30-m water depth and the

spatial extend of the accumulation patterns

depends strongly on the settling velocity used in

the model.

We expect that the results of this study offer useful

clues to potential seed regions of algae. From our

time-slice experiments, we conclude that cysts, which

are produced in late summer in the shallow regions,

are transported during autumn and winter into the

deeper parts of the Baltic. In the model calculation,

the material accumulates in the slope regions of the

deep basins which therefore could be expected as

potential seed regions.

Furthermore, we have estimated potential erosion

and deposition areas. The potential erosion areas are

displayed in Fig. 7. Model calculations with im-

proved horizontal resolution are planned to investi-

gate the transport paths of material eroded in these

areas. Since the stability of sediments against ero-

sion can be changed substantially by benthic organ-

isms, detailed data on the distribution of benthic

communities and their influence on the sediment

properties are needed to yield better model predic-

tions. Assuming a resuspension threshold of 0.5 cm/

s, fine material will be finally deposited in the

deeper parts of the Baltic (see Fig. 8). These results

are in accordance with the observed distribution of

mud and silt (see, e.g. the sediment map of Nielsen,

1992b).

Further investigations will be focused on a more

direct comparison to and interaction with measure-

ments. The presented model experiments gave some

indications how the model system as well as the input

data should be improved. The calculated accumula-

tion patterns of fluffy layers strongly depend on the

chosen value of the settling velocity. Therefore, reli-

able parameterizations of this quantity are essential for

realistic simulations. Observations (see, e.g. Jahmlich

et al., 2002) show strong seasonal variations of the

aggregate size and settling velocities of fluffy material

in the Baltic, which must be taken into account in

future model versions.

Since the central parts of the basins are known as

the final deposition areas, the following question

arises: how the fine material is transported from the

slopes into the centers of the basins? We cannot

exclude that the near-bottom currents are underesti-

mated by the model. However, bioresuspension due to

benthic organisms can provide fluxes of sedimentary

material into the bottom boundary layer which can be

of some importance in the slope regions of the deep

basins. Therefore, the integration of these processes

into the bottom boundary layer model is planned in

further studies.

Acknowledgements

We thank Christian Christiansen for helpful and

constructive recommendations. B. Bobertz has kindly

provided the sediment map needed for the model

simulations and M. Schmidt provided assistance with

the MOM 3.1. The work was supported by the Federal

Ministry of Education and Research (BMBF) in the

frame of the DYNAS Project (No. 03F0280A).

References

Amos, C.L., Feeney, T., Sutherland, T.F., Luternauer, J.L., 1997.

The stability of fine-grained sediments from the Fraser River

Delta. Estuarine, Coastal and Shelf Science 45, 507–524.

Austen, I., Andersen, T.J., Edelvang, K., 1999. The influence of

Benthic Diatoms and Invertebrates on the erodibility of an in-

tertidal mudat, the Danish Wadden Sea. Estuarine, Coastal and

Shelf Science 49, 99–111.

Black, K.P., Vincent, C.E., 2001. High-resolution field measure-

ments and numerical modelling of intra-wave sediment suspen-

sion on plane beds under shoaling waves. Coastal Engineering

42 (2), 173–197.

Bohling, B., 2002. Sedimentological parameters as a basis for

investigations on sediment dynamics in the Mecklenburg Bay.


In: Emelyanov, E.M. (Ed.). The Seventh Marine Geological

Conference ‘‘Baltic-7’’, Abstracts, Kaliningrad (Russia).

Bohling, B., 2003. Studies on the mobility of natural and anthro-

pogenic sediments in the Meddenburgian Bay, PhD thesis Fac-

ulty of Mathematics and Sciences, University of Greifswald.

Bouws, E., Guenther, H., Rosenthal, W., Vincent, C.L., 1985. Sim-

ilarity of the wind wave spectrum in finite depth water: 1. Spec-

tral form. Journal of Geophysical Research 90 (C1), 975–986.

Christiansen, C., Edelvang, K., Emeis, K., Graf, G., Jahmlich, S.,

Kozuch, J., Laima, M., Leipe, T., Loffer, A., Lund-Hansen,

L.C., Miltner, A., Pazdro, K., Pempkowiak, J., Shimmield, G.,

Shimmield, T., Smith, J., Voss, M., Witt, G., 2002. Material

transport from the nearshore to the basinal environment in the

southern Baltic Sea I. Processes and mass estimates. Journal of

Marine Systems 35, 133–150.

Emeis, K.-C., Struck, U., Leipe, T., Pollehne, F., Kunzendorf, H.,

Christiansen, C., 2000. Changes in the C, N, P burial rates in

some Baltic Sea sediments over the last 150 years—relevance to

P regeneration rates and the phosphorus cycle. Marine Geology

167, 43–59.

Fennel, W., Sturm, M., 1992. Dynamics of the western Baltic.

Journal of Marine Systems 3, 183–205.

Fredsoe, J., Deigaard, R., 1992. Mechanics of Coastal Sediment

Transport. World Scientific, Singapore.

Gerritsen, H., Boon, J.G., van der Kaaij, T., Vos, R.J., 2001. Inte-

grated modelling of suspended matter in the North Sea. Estua-

rine, Coastal and Shelf Science 53, 581–594.

Grant, W.D., Madsen, O.S., 1979. Combined wave and current

interaction with a rough bottom. Journal of Geophysical Re-

search 84 (C4), 1797–1808.

Griffies, S.M., Pacanowski, R.C., Schmidt, M., Balaji, V., 2001.

Tracer conservation with an explicit free surface method for z-

coordinate ocean models. Monthly Weather Review 129,

1081–1098.

Hasselmann, K., Barnett, T.P., Bouws, E., Carlson, H., Cartwright,

D.E., Enke, K., Ewing, J.A., Gienapp, H., Hasselmann, D.E.,

Kruseman, P., Meerburg, A., Muller, P., Olbers, D.J., Richter,

K., Sell, W., Walden, H., 1973. Measurements of wind-wave

growth and swell decay during the Joint North Sea Wave Project

(JONSWAP). Deutsche Hydrographische Zeitschrift A12, 1–95.

Holt, J.T., James, I.D., 1999. A simulation of the southern North

Sea in comparison with measurements from the North Sea Proj-

ect Part 2 suspended particulate matter. Continental Shelf Re-

search 19, 1617–1642.

Jahmlich, S., Lund-Hansen, L.C., Leipe, T., 2002. Enhanced set-

tling velocities and vertical transport of particulate matter by

aggregation in the benthic boundary layer. Geografisk Tidskrift,

Danish Journal of Geography 102, 37–49.

Jankowski, J.A., Malcherek, A., Zielke, W., 1996. Numerical mod-

elling of suspended sediment due to deep sea mining. Journal of

Geophysical Research 101 (C2), 3545–3560.

Janssen, F., Schrumm, C., Backhaus, J.O., 1999. A climatological

dataset of temperature and salinity for the North Sea and the

Baltic Sea. Deutsche Hydrographische Zeitschrift. Supplement

9, 245.

Kitaigorodskii, S.A., Krasitskii, V.P., Zaslavskii, M.M., 1975. On

Phillips’ theory of equilibrium range in the spectra of wind-

generated gravity waves. Journal of Physical Oceanography 5,

410–420.

Large, W.G., McWilliams, J.C., Doney, S.C., 1994. Oceanic vertical

mixing: a review and a model with a nonlocal boundary layer

parameterization. Review of Geophysics 32, 363–403.

Liu, P.C., Schwab, D.J., Jensen, R.E., 2001. Has wind wave mod-

eling reached its limit? Ocean Engineering 29, 81–98.

Lou, J., Ridd, P.V., 1997. Modelling of suspended sediment trans-

port in coastal areas under waves and currents. Estuarine, Coast-

al and Shelf Science 45, 1–16.

Lou, J., Schwab, D.J., Beletsky, D., Hawley, N., 2000. A model of

sediment resuspension and transport dynamics in the southern

Lake Michigan. Journal of Geophysical Research 105 (C3),

6591–6610.

Meyer-Peter, E., Muller, R., 1948. Formulas for bed-load transport.

Rep. 2nd Meet. Int. Assoc. Hydr. Struct. Res. Stockholm 1948,

pp. 39–64.

Nielsen, P., 1983. Analytical determination of nearshore wave

height variation due to refraction shoaling and friction. Coastal

Engineering 7, 233–251.

Nielsen, P., 1992a. Coastal bottom boundary layer and sediment

transport. Advanced Series on Ocean Engineering, Edition 4,

World Scientific.

Nielsen, P.E., 1992b. Bottom sediments around Denmark and west-

ern Sweden. Geological Survey of Denmark (DGU), Map Series

no. 38. Scale 1:500000.

Pacanowski, R.C., Griffies, S., 2000. MOM 3.0 Manual. Technical

report Geophysical Fluid Dynamics Laboratory, Princeton

(USA).

Puls, W., Sundermann, J., 1990. Simulation of suspended sediment

dispersion in the North Sea. Residual Currents and Long Term

Transport. Springer Verlag, New York, pp. 356–372.

Puls, W., Doerffer, R., Sundermann, J., 1994. Numerical simulation

and satellite observations of suspended matter in the North Sea.

Journal of Oceanographic Engineering 19 (1), 3–9.

Ribbe, J., Holloway, P.E., 2001. A model of suspended sediment

transport by internal tides. Continental Shelf Research 21,

395–422.

Schmidt, M., Seifert, T., Lass, H.U., Fennel, W., 1998. Patterns of

salt propagation in the southwestern Baltic Sea. Deutsche

Hydrographische Zeitschrift 50 (4), 345–364.

Schwab, D.J., Bennett, J.R., Liu, P.C., Donelan, M.A., 1984.

Application of a simple numerical wave prediction model

to Lake Erie. Journal of Geophysical Research 89 (C3),

3586–3592.

Schwarzer, K., Diesing, M., Larson, M., Niedermeyer, R.-O.,

Schumacher, W., Furmanczyk, K., 2003. Coastline evolu-

tion at different time scales—examples from the Pomera-

nian Bight, southern Baltic Sea. Marine Geology 194, 79–

101.

Seifert, T., Tauber, F., Kayser, B., 2001. A high resolution spherical

grid topography of the Baltic Sea—revised edition. http://

www.iowarnemuende.de/admin/de_index.html.

Smagorinsky, J., 1993. Some historical remarks on the use of non-

linear viscosities. In: Galperin, O. (Ed.), Large Eddy Simulation

of Complex Engineering and Geophysical Flows Cambridge

Univ. Press, Cambridge, pp. 3–36. Chap. 1.

http://www.iowarnemuende.de/admin/de_index.html


Smith, J.D., McLean, S.R., 1977. Spatially averaged flow over a

wavy surface. Journal of Geophysical Research 82 (12),

1735–1746.

Soulsby, R.L., 1997. Dynamics of Marine Sands, A Manual for

Practical Applications. Thomas Telford, London.

Tiepolt, L., Schumacher, W., 1999. Historische bis rezente Kusten-

veranderungen im Raum Fischland-Darss-Zingst-Hiddensee

anhand von Karten, Luft-und Satellitenbildern. Die Kuste 61,

21–46.

Tolhurst, T.J., Riethmuller, R., Patterson, D.M., 2000. In situ versus

laboratory analysis of sediment stability from intertidal mud-

flats. Continental Shelf Research 20, 1317–1334.

van Wijngaarden, M., Roberti, J.R., 2002. In situ measurements of

settling velocity and particle size distribution with the LISST-

ST. In: Winterwerp, J.C., Kranenburg, C. (Eds.), Fine Sedi-

ment Dynamics in the Marine Environment. Elsevier Science,

Amsterdam, pp. 295–311.

Winterwerp, J., 1989. Flow induced erosion of cohesive beds.

Rijkswaterstaat-Delft Hydraulics. Report 25.

Xu, J.P., Wright, L.D., 1995. Tests of bed roughness models using

field data from the middle Atlantic Bight. Continental Shelf

Research 15 (11/12), 1409–1434.

Yalin, M.S., 1977. Mechanics of Sediment Transport. Pergamon

Press, New York. 298 pp.

Zanke, U., 1982. Grundlagen der Sedimentbewegung Springer-

Verlag, Berlin.

Ziervogel, K., Bohling, B., 2003. Sedimentological parameters

and erosion behaviour of submarine coastal sediments in the

south-western Baltic Sea. Geo-Marine Letters Online First.

10.1007s00367-003-0123-4.

Documents

Model studies of transport of sedimentary material in the western Baltic