Redistribution of sediments in three Swedish lakes

Sedimentation and redistribution of fine sediments in three Swedish lakes of different character have been investigated using settling sediment traps. The bottom shear stress from wind generated waves are calculated and the extension of erodable bottom area is related to wind conditions. Wave induced erosion and deposition during and after cessation of storms in different parts of a lake are discussed theoretically. It is shown that a single one year storm may redistribute more bottom material than the accumulated resuspension caused by frequent but smaller wind events. The settling sediment trap deposition and the concentration of suspended solids are related to the extension of erodable bottom area of particular storms. It is found that in lakes where there are relatively large areas of erosion bottoms, resuspended material from the part of the lake most susceptible to strong winds of large fetch constitutes a major part of the settled material on deep bottoms.     

Interpretation of sedimentation data measured in a former tidal channel Lake Volkerak

In Lake Volkerak, situated in the southwest of the Netherlands, downward settling fluxes are related to external inputs of suspended solids and wind action. The settling fluxes, measured using sediment traps, were 55 g (dw) m ^–2 d ^–1 on average. The ratio of metal concentration to scandium concentration was used to discriminate between external (polluted) suspended solids and internal (relatively clean) suspended solids. Generally, the contribution of the river suspended solids was small compared to that of resuspended material; the river-transported material was mainly deposited in the centre and to the east of the lake. The amount of material trapped increased substantially with increasing wind velocity.A simple model was used to interpretate the data. This model does not have a predictive capacity, but can be used to interpret and assess the significance of material retained in the sediment traps. Erosion was related to the wind velocity, using an empirical relationship between the orbital velocity of the wind-generated waves at the bottom and the wind velocity. The critical wind velocity for erosion to occur was estimated to be 5.5 m s^–1. The extremely high amounts retained in the sediment traps in shallow areas during storms emphasised the importance of these wind conditions for the transport of fine sediments.     

Siltation of stone-surface periphyton in rivers by clay-sized particles from low concentrations in suspention

The observation that deposits of fine sediment are found on stream beds only in areas of slower water velocity promotes a common misunderstanding of the depositional behaviour of fine suspensoids in flowing water and a disregard for the potential for siltation effects on the biota on the surface of stones in fast flowing water. A model for deposition from turbulent water, whereby particles are lost from suspension where water currents are slowed by boundary friction, provides an explanation for silt infiltration into epilithic periphyton. Theoretically calculated deposition rates of clay sized mineral particles at low suspended concentrations (2 to 5 g m^–3) were found to account for observed rates of silt accumulation in epilithic periphyton in a braided river in the South Island of New Zealand. At concentrations between 1 and 10 g m^–3 of suspended mineral silt during normal flow, silt accumulation in epilithic periphyton accounted for about 50% of its dry weight. This caused a reduction in the mean organic content of the periphyton to 22% of the dry weight compared to 52% in a reference stream where the concentration of suspended mineral particles was less than 1.0 g m^–3 during non-freshet flow. This reduction in proportional organic content is discussed in terms of diminished food value of the periphyton and potential interactions between periphyton and invertebrate consumers.     

土壤有机碳动态:风蚀效应

土壤风蚀是引起土壤退化最广泛的形式和原因之一。土壤风蚀对土壤碳动态的影响机制一方面是土壤风蚀引起土壤退化使土壤生产力下降,输入土壤的碳数量减少;另一方面是富含有机碳的细粒物质直接移出系统。风蚀土壤碳的去向包括:(1)就近沉积,(2)沉积于水渠和河流,输入水体;(3)以粉尘形式运移,在远离风蚀区的地域沉积;(4)氧化释放至大气。风蚀引起土壤碳的迁移和沉积不仅导致土壤有机碳在地域间的再分布,使土壤性状的空间异质性增加,也显著改变了土壤系统中碳矿化的生物学过程。土壤有机碳的保持可以促进团聚体的形成,使土壤物理稳定性增加,减缓风蚀。对易风蚀土地进行退耕还林还草、实行保护性耕作等措施可以有效增加土壤碳的固存。     

Role of climate and agricultural practice in determining matter discharge into large,shallow Lake Võrtsjärv,Estonia

Understanding the dynamics of fine sediment transport across the upper intertidal zone is critical in managing the erosion and accretion of intertidal areas, and in managed realignment/estuarine habitat recreation strategies. This paper examines the transfer of sediments between salt marsh and mudflat environments in two contrasting macrotidal estuaries: the Seine (France) and the Medway (UK), using data collected during two joint field seasons undertaken by the Anglo-French RIMEW project (Rives-Manche Estuary Watch). High-resolution ADCP, Altimeter, OBS and ASM measurements from mudflat and marsh surface environments have been combined with sediment trap data to examine short-term sediment transport processes under spring tide and storm flow conditions. In addition, the longer-term accumulation of sediment in each salt marsh system has been examined via radiometric dating of sediment cores. In the Seine, rapid sediment accumulation and expansion of salt marsh areas, and subsequent loss of open intertidal mudflats, is a major problem, and the data collected here indicate a distinct net landward flux of sediments into the marsh interior. Suspended sediment fluxes are much higher than in the Medway estuary (averaging 0.09 g/m³/s), and vertical accumulation rates at the salt marsh/mudflat boundary exceed 3 cm/y. Suspended sediment data collected during storm surge conditions indicate that significant in-wash of fine sediments into the marsh interior can occur during (and following) these high-magnitude events. In contrast to the Seine, the Medway is undergoing erosion and general loss of salt marsh areas. Suspended sediment fluxes are of the order of 0.03 g/m³/s, and the marsh system here has much lower rates of vertical accretion (sediment accumulation rates are ca. 4 mm/y). Current velocity data for the Medway site indicate higher velocities on the ebb tide than occur on the flood tide, which may be sufficient to remobilise sediments deposited on the previous tide and so force net removal of material from the marsh.     

Import of fine marine sediment in tidal areas

Summary In many estuaries the observed import of fine marine sediment can be explained by the presence of a gravitational circulation, which is driven by the longitudinal density gradient caused by fresh water inflow. Examples are the Thames, the Gironde, Columbia river and Savannah river. With this transport mechanism a turbidity maximum is present near the upstream boundary of the gravitational circulation. Even in vertically well mixed estuaries, where the contribution of gravitational circulation to the residual salt transport is of minor importance, the influence on the residual sediment transport may be considerable.In tidal basins with no river inflow, or with a relatively small river inflow as compared to the average tidal discharge (<Q>²/<Q²>0.01) no significant gravitational circulation is present. Yet a residual sediment transport and a landward increase of the suspended sediment concentration is experimentally observed in this type of tidal basins. However, the turbidity maximum characteristic for inhomogeneous estuaries is absent. In an estuary, sediment may accumulate on the bottom in regions where the shear stress from tidal currents and wind waves does not exceed some critical value. The rate of accumulation depends on the capacity of the current velocity field to transport sediment from the seaboundary to the sedimentation areas. The exchange of estuarine waters and seawater by horizontal circulations or shear diffusion is not responsible for this residual import of sediment. These exchange processes would lead to an export instead of an import of sediment as a consequence of the higher suspended sediment concentration of the estuarine waters.Some thirty years ago, Postma pointed out a class of sediment transport mechanisms which may explain the import of marine sediment in homogeneous tidal basins. These mechanisms are based on the existence of an ebb-flood asymmetry in the cycle of sedimentation, erosion and subsequent tidal displacement of sediment. An ebb-flood asymmetry must be understood here as follows: certain tidal characteristics designated here by f (for example the current velocity, or the bottom shear stress), evaluated in a frame moving with the cross-sectionally averaged tidal velocity, violate the equality f(t)+f(t+1/2 T)=0, where T is the length of the tidal period. The net displacement of sediment due to such an ebb-flood asymmetry is called tide-induced residual sediment transport. The geometrical configuration of a tidal basin determines to a large extent the ebb-flood asymmetry. For example, a strong decrease of the relative bottom depth, which occurs in the landward part of a tidal basin, causes an ebb-flood asymmetry due to which the import of fine sediment exceeds the export.The tide-induced residual import of marine sediment is not sufficient in itself to explain the experimentally observed increase of suspended sediment in the landward part of a tidal basin. An increase of the suspended sediment concentration would be expected there where the capacity of the residual landward transport decreases (cf. the turbidity maximum near the landward limit of gravitational circulation). Generally, however, the capacity of the tide-induced residual transport increases in landward direction, as a result of which the suspended sediment concentration can be expected to decrease. This apparent contradiction can be explained by the action of wind waves, which may, at irregular intervals, bring back into suspension large amounts of sediment which have settled under less severe wave conditions. Wind action may also change the tide-induced residual sediment import into export in the shallow landward part, causing a redistribution of sediment inside the tidal basin. The time that fine marine sediment remains in suspension inside the tidal basin is therefore strongly increased by the action of wind waves.The influence of gravitational circulation on the net import of fine sediment in estuaries is illustrated with field data collected in the Rotterdam Waterway and the western Waddensea. The tide-induced residual sediment transport is shown to be the major transport process in large parts of the eastern Waddensea and the Oosterschelde Basin. It provides a quantitative explanation of the experimentally observed import of fine sediment in the former and export in the latter tidal system.     

The effects of rain on the erosion threshold of intertidal cohesive sediments

Intertidal sedimentary environments are complex systems governed by interactions between physical, chemical and biological processes and parameters. Tidally induced flow and wave action are known to be an integral driving force behind the erosion, transport, deposition and consolidation cycle (ETDC) of intertidal sediments. Whilst considerable advances have been made in understanding both the physical and biological processes and their interactions in these systems, it is clear that there are gaps in our understanding. One factor that has been largely ignored to date is that of rain. Visual observations in the field and associated data indicated that rain showers during low tide are correlated with a reduction in the erosion threshold of intertidal cohesive sediments. This paper presents preliminary field and laboratory data showing the importance of rain in reducing the erosion threshold of cohesive intertidal sediments. The implications for our knowledge of, and modelling of the ETDC cycle of cohesive intertidal sediments are discussed.     

Characterising the fine sediment budget of a reach of the River Swale,Yorkshire, U.K. during the 1994 to 1995 winter season

Suspended sediment budget dynamics for a 55 km reach of the lowland River Swale, Yorkshire, U.K. are investigated for the period October 1994 to June 1995. Particular attention is paid to 11 storm events occurring between October 1994 and April 1995. Each of these storms produced significant suspended sediment transport. Variations in sediment dynamics, for example suspended sediment concentrations, hysteresis patterns and storm peak lag times through events and between the upstream and downstream ends of the reach are examined. Net sediment loss from the reach occurred during the extremely wet four month winter period from December 1994 to April 1995. Patterns of reach sediment storage are concluded to represent a combination of channel bed erosion and/or deposition, bank erosion and floodplain deposition. The implications of these patterns for sediment modelling are discussed.     

The turbidity maximum in the Tamar estuary

Many estuaries of medium to high tidal range exhibit an accumulation of fine cohesive material in their upper reaches in the region of the limit of saline intrusion. Much, or all, of this material is suspended each tidal cycle and the entire region undergoes a seasonal variation which appears to depend on fluvial input. Two factors which are throught to influence the formation and maintenance of turbidity maxima are the differing magnitudes of the bed shear stress (τ₀) on flood and ebb tides and the large vertical density gradient which developes on the ebb tide. Crucial to the importance of the first factor is that τ₀ exceeds a critical value, at which erosion occurs, for a greater period on the flood than on the ebb. The effect of the density gradient is that upward propagation of bed generated eddies is inhibited and the sediment is not transported into the upper part of the flow where it will be most effectively transported. It is not clear which, if either, of these mechanisms is dominant. Data consisting of vertical profiles of velocity, salinity and suspended solids were collected at four stations in the Tamar estuary during a high range tidal cycle. One station, at which the depth mean salinity (S _d ) varied from 0.0 to ∼ 12.0‰, was occupied permanently. The other stations were occupied such that data were collected asS _d varied in the range 0.0 to ∼ 4.0‰. In this way each station was occupied for a period of time on the ebb and flood tide. Observations show that during the early ebb, when the flow is relatively deep and slow, stratification persist untilS _d ∼ 0.0‰ and that no significant transport occurs while the flow is saline but that there is a rapid increase in suspended solids concentrations after this time. During the later ebb the shallower faster flow allowed the density gradient to be erode and significant transport was observed atS _d ∼ 5.0‰. On the flood tide the flow in the low salinity region is well-mixed troughout. Computation of the fluxes and total transport per unit breath of estuary show that on the ebb tide the quantity of solid material being transported by the low salinity (0–3‰) region remains nearly constant as this region of the flow is advebted seaward. On the flood tide, however, as the same region is advected landward the quantity of material being transported increases. It is concluded that in the Tamar estuary the early ebb tide stratification contributed to the formation and maintenance of a turbidity maximum which is strongly associated with the low salinity region of the flow. It is also speculated that the differences in the ebb and flood tide transport are caused by differences in the availability of mobile material on the bed at different stages of the tidal cycle.     

3D-numerical modelling of cohesive suspended sediment in the Western Scheldt estuary (The Netherlands)

A cohesive sediment transport model considering the effects of flocculation, deposition and erosion is used in an attempt to simulate the suspended sediment distribution in a mesotidal estuary. The numerical model solves the three-dimensional (3D) advection-diffusion equation using a two-time level scheme, and a semi-implicit finite difference approach. The transport model is coupled to a 3D-barotropic hydrodynamic model for the simulation of the major tidal components reproducing the non-linear effects. An application of these models in the Western Scheldt estuary is described. The results of the different tests show that the adopted approach provides a useful basis for a good understanding of the physical processes involved in sediment transport and for the study of practical problems. The sensitivity of the model to key parameters controlling the simulation of bed sediment/water exchanges, shows the importance of a good definition of bottom sediment characteristics and the importance of further development of a consolidation algorithm.     

Coupling satellite data with in situ measurements and numerical modeling to study fine suspended-sediment transport: a study for the lagoon of New Caledonia

This paper investigates the potential of remotely sensed data to map turbidity in a coral reef lagoon and to calibrate a numerical model of fine suspended-sediment transport. Simultaneous measurements of turbidity depth-profile and above-water spectral reflectance integrated according Landsat 7 ETM+ band 2 spectral sensitivity provide a linear regression relationship for the southwest lagoon of New Caledonia (r²=0.95, n=40). This relationship is applied to an empirically atmospherically corrected Landsat ETM+ image of the lagoon acquired on October 23, 2002. A comparison between Landsat estimates of turbidity and concurrent measurements at 14 stations indicates that the mean standard error in the satellite-estimated turbidity is 17.5%. The numerical model introduced in Douillet et al. (2001) is used to simulate the transport of fine suspended sediments in the lagoon in October 2002. A calibration of the erosion rate coefficient required by the model is proposed using in situ turbidity profiles and the remotely sensed turbidity field. In situ data are used to tune locally the erosion rate coefficient, while satellite data are used to determine its spatial zonation. We discuss necessary improvements in coupled studies of fine-sediment transport in coastal zones, namely relationships between turbidity and sediment concentration, integration of wave influence in the model, and correction of bottom reflection in satellite data processing.     

Modelling sediment transport in shallow lakes — interactions between sediment transport and sediment composition

In shallow, wind exposed lakes, the light conditions, the cycling of nutrients, heavy metals and organic micro-pollutants and changes in the local composition of the sediment top layer can be dominated by resuspension/erosion of bottom sediment and sedimentation of suspended solids. A 2 dimensional model for Sediment Transport, Resuspension and Sedimentation in Shallow lakes (STRESS-2d), based on an existing transport model, is discussed. In the model, mass balance equations for the water compartment and the bottom sediment are solved numerically. Up to 7 sediment fractions can be taken into account, each having a specific set of resuspension/erosion and sedimentation parameter values. Several options for modelling the changes in the bottom sediment composition are available.A simulation experiment for Lake Veluwe (The Netherlands), in which model options with and without the distinction of sediment fractions were used, showed that using sediment fractions to account for the variability in the sediment composition leads to an improvement of the model results, particularly the simulated phosphorus sediment-water exchange fluxes. For Lake Ketel (The Netherlands) two options for modelling changes in the bottom sediment composition are compared. It is shown that an option in which a thin water-sediment layer on top of the more consolidated bottom sediment is simulated provides an improvement in the simulation of the suspended solids concentration.     

Modelling sand/mud transport and morphodynamics in the Seine river mouth (France): an attempt using a process-based approach

The mouth of the Seine River estuary (France) has undergone marked morphological evolution over several decades mainly due to engineering works aimed at improving access to Rouen and Le Havre harbours. The intertidal areas are decreasing in size and the lower estuary is accumulating sediment and prograding. In order to understand and better describe the major morphological behaviours of the estuary, a morphodynamic numerical model was developed within the Seine-Aval program. At the end of the 1st part of the research program, a validated fine sediment transport model (3D) was available (Le Hir et al., 2001b). As the present morphological study addresses medium-term issues (a few decades), and because of the need to investigate impacts of local structures or events, we chose to use the so-called “process-based approach” starting from the existing model. First, the existing model was upgraded to account for (suspended) sand transport, and to achieve coupling between morphological changes and sediment transport. Erodability of the sediment accounts for the respective proportions of mud and sand. Simulations starting from an arbitrary surficial sediment cover show that the model is able to reproduce realistic sediment patterns. For example, it is able to change the sediment nature on the intertidal flat near Le Havre from sand to mud. Observed structures of suspended sediment are also reproduced: fine particles mainly follow the turbidity maximum whereas significant concentrations of sand grains in suspension are found where the hydrodynamic stresses are intense. Concerning morphodynamics, simulations with real forcing over one year are discussed. The effect of waves on the bathymetric evolution of the mouth is shown and the sensitivity of morphodynamics to the coupling procedure is tested.     

Pedoecological effects of a sand-fixing poplar (Populus simonii Carr.) forest in a desertified sandy land of Inner Mongolia, China

To assess the pedoecological effects of a 23-year old poplar ( Populus simonii Carr.) forest on soil amelioration and vegetation restoration via soil erosion reduction and atmospheric dust retention in a desertified sandy land ecosystem, daily dynamics of wind speed, sand transport and dust deposition rates were monitored over an erosive period from April through June in 2001, using fixed observation sites located at different positions within and around the forest. Soil and vegetation characteristics at these sites were also measured. The observation sites were placed at distances of 15H (as control), 6H and 3H (H is mean tree height) from the forest edge of the windward side (abbreviated CK, 6H-W and 3H-W respectively), forest center (FC), and at distances of 0H, 6H and 8H from the forest edge of the leeward side (FE-L, 6H-L and 8H-L respectively). Daily mean wind speed was significantly lower in different observation sites than CK, with FC having the greatest reduction of wind speed and 6H-W the least reduction. Daily transport rate of sand by wind was also significantly lower in different observation sites than CK, with FE-L having the greatest reduction of wind erosion and 6H-W the least reduction. The fact that the poplar forest will lose its functions against wind at a distance of about 12-fold tree height from the forest edge of the leeward side suggests that the effective wind-preventing range of the poplar forest is about 150 m. There was marked spatial and seasonal distribution of dust-fall rate. Over space, the rate of dust-fall was much greater within the forest than outside the forest. Over time, the daily dust deposition rate was greatest in April, followed in decreasing order by May, June, July, September and August, closely linked to the seasonal distribution pattern of dust storm. Significant positive changes in soil and vegetation parameters of the different observation sites during the 23 years that the poplar forest was established suggest the perceptible pedoecological effects of the poplar forest on soil development and restorative succession of plant community within its immediate vicinity through windbreak, soil erosion reduction and atmospheric dust retention. Understanding these pedoecological effects may aid in the design of protective forest systems in arid and semi-arid areas.     

Determination of urban pollution islands by using remote sensing technology in Moscow,Russia

Pollution of the atmosphere with harmful substances is currently the most dangerous form of degradation of the natural environment in Russia. The peculiarities of the environmental situation and the emerging environmental problems in some areas of the Russian Federation are caused by local natural conditions and the nature of the impacts from industries, transport, utilities, and agriculture (the specifics of enterprises, their capacity, location, technologies used). As a rule, the magnitude of air pollution depends on the degree of urbanization and anthropogenic transformation of the territory and climatic conditions that determine the potential for atmospheric pollution. During high-temperature technological processes, the smallest aerosol particles (0.5..0.10 μm) formed, poorly captured by gas purification plants, and can migrate in the atmosphere for considerable distances. Larger particles (2.5 μm and above) are formed due to the mechanical decomposition of solid particles and enter the atmosphere due to wind erosion, the dusting of dirt roads, the erasure of vehicle tires. The particles suspended with a diameter of not more than 2.5 μm (PMX) are the most destructive to health since they penetrate and get deposited deep into human lungs. These microns, present in a suspended state in the air, consist of a complex mixture of large and small, solid and liquid particles, of both inorganic and organic substances. The boundary between the two fractions is usually particles with a diameter of 2.5 μm (PM2.5). This study sought to build a model for determining fine dust PM2.5 in the Moscow air environment using Landsat 8 OLI satellite image channels and data on the concentrations of fine dust PM2.5 obtained by weather stations in the city. In addition, a correlation analysis was carried out to determine a regression model for studying the dispersion of fine dust in the city. The results obtained are presented on a map of the concentration of fine dust PM2.5 in Moscow, supporting management decisions and decision-making on environmental policy in urban planning.     

植被覆盖对风蚀地表保护作用研究的某些新进展

 植被覆盖在风蚀过程中可通过多种途径保护地表土壤,减少风蚀输沙,对此人们早已有所认识。然而,在植被覆盖防护效应的定量研究方面,却长期存在着严重不足。近年来,国外学术界在植被覆盖保护作用的机理和定量研究等多个方面取得了突破性进展,国内却仍处于起步阶段。在大量总结国内外最新文献基础上,从理论研究、观测实验和定量模型3个方面,就植被覆盖对风蚀地表保护作用研究的新进展进行了系统介绍和评述,并结合当前国内的研究状况和现实需要,提出了4个有待进一步深入研究的重点问题。     

Numerical modelling of suspended sediment transport in tidal estuaries: A comparison between the Tagus (Portugal) and the Scheldt (Belgium-the Netherlands)

A numerical model to simulate the transport of suspended sediment in tidal estuaries is presented. The model is applied to the two large European estuaries the Tagus (Portugal) and the Scheldt (Belgium-The Netherlands). Calculated suspended sediment concentrations compare favourably with observations in the Tagus (r=0.84) and in the Scheldt (r=0.73). The parametrization scheme indicates that the bottom content of fine sediment is correlated with depth in the Tagus; but a different relationship is used in the Scheldt. Because of tidal range differences, average suspended sediment concentrations are lower in the Tagus (80 mg l⁻¹) than in the Scheldt (130 mg l⁻¹), but a larger relative variation between spring and neap tide concentrations may occur in the Tagus.     

Aspects of modelling sediment transport and night conditions in Lake Marken

In lake Marken (Markermeer), a shallow lake in the Netherlands, sediment transport and suspended solids concentration are dominated by wind induced resuspension of sediment. The suspended solids concentration in the lake determines the attenuation of light. A 2-dimensional sediment transport model, STRESS-2d, was used to estimate the special distribution of the silt content for periods with different wind conditions. The model was calibrated using measured values of the fall velocity distributions of sediment, freshly deposited material and suspended solids. The specific light attenuation coefficient of the various sediment classes was also measured and used in the light attenuation model, CLEAR, together with simulation results from the STRESS-2d model, to simulate the light attenuation variations in time and space. By comparison of the simulation results for different scenarios, the influence of regional planning features on the sediment balance and the light attenuation can quantified. A provisional example of this method is presented.     

Hydrodynamic and sediment transport modeling with emphasis on shallow-water,vegetated areas (lakes,reservoirs, estuaries and lagoons)

Modeling capabilities for shallow, vegetated, systems are reviewed to assess hydrodynamic, wind and wave, submersed plant friction, and sediment transport aspects. Typically, ecosystems with submersed aquatic vegetation are relatively shallow, physically stable and of moderate hydrodynamic energy. Wind-waves are often important to sediment resuspension. These are open systems that receive flows of material and energy to various degrees around their boundaries. Bed shear-stress, erosion, light extinction and submersed aquatic vegetation influence each other. Therefore, it is difficult to uncouple these components in model systems. Spatial changes in temperature, salinity, dissolved and particulate material depend on hydrodynamics. Water motions range from wind-wave scales on the small end, which might be important to erosion, to sub-tidal or seasonal scales on the large end, which are generally important to flushing. Seagrass modifies waves and, therefore, affects the relationships among the non-dimensional scaling parameters commonly used in wave analysis. Seagrass shelters the bed, often causing aggradation and changes in grain size, while increasing total resistance to flow. Hydrodynamic friction can not be well characterized by a single-parameter equation in seagrass beds, and models need appropriate enhancement when applied to these systems.Presently, modeling is limited by computational power, which is, however, improving. Other limitations include information on seagrass effects expressed in frictional resistance to currents, bed-sheltering, and wave damping in very shallow water under conditions of both normal and high bed roughness. Moreover, quantitative information on atmospheric friction and shear stress in shallow water and seagrass areas are needed. So far, various empirical equations have been used with wind or wave forcing to describe resuspension in shallow water. Although these equations have been reasonably successful in predicting suspended sediment concentrations, they require site-specific data. More detailed laboratory and field measurements are needed to improve the resuspension equations and model formulation pertaining to seagrass beds.