Suspended sediment modelling in a shelf sea (North Sea (original) (raw)
Continental Shelf Research, 1999
We simulate the distribution of suspended particulate matter in the southern North Sea using a three-dimensional baroclinic shelf-sea model. Process studies with individual coastal sources show the transport of material across the southern North Sea and out into the Norwegian trench is sensitive to specific wind conditions and settling velocities, so that material which settles during the summer can be transported faster than a passive tracer if its flux is unidirectional. Results from model runs with a number of coastal sources and size classes are compared with CTD data from the North Sea Project, using multiple linear regression to estimate the source strengths. The agreement is best during the winter, with correlation coefficients greater than 0.7; this falls below 0.4 in the summer. We estimate the input from Holderness and the Wash to be 5.6 M tonnes/year, and from the East Anglian coast to be 2.1 M tonnes/year. Due to the limited resolution of the model and the observations, we find we are unable to estimate the input from the English Channel or the Rhine with any degree of certainty.
Continental Shelf Research, 1999
We simulate the distribution of suspended particulate matter in the southern North Sea using a three-dimensional baroclinic shelf-sea model. Process studies with individual coastal sources show the transport of material across the southern North Sea and out into the Norwegian trench is sensitive to speci"c wind conditions and settling velocities, so that material which settles during the summer can be transported faster than a passive tracer if its #ux is unidirectional. Results from model runs with a number of coastal sources and size classes are compared with CTD data from the North Sea Project, using multiple linear regression to estimate the source strengths. The agreement is best during the winter, with correlation coe$cients greater than 0.7; this falls below 0.4 in the summer. We estimate the input from Holderness and the Wash to be 5.6 M tonnes/year, and from the East Anglian coast to be 2.1 M tonnes/year. Due to the limited resolution of the model and the observations, we "nd we are unable to estimate the input from the English Channel or the Rhine with any degree of certainty.
A revised dynamic model for suspended particulate matter (SPM) in coastal areas
Aquatic Geochemistry, 2006
This paper presents a general, process-based model for suspended particulate matter (SPM) in defined coastal areas (the ecosystem scale). The model is based on ordinary differential equations and the calculation time (dt) is 1 month to reflect seasonal variations. The model has been tested using data from 17 Baltic coastal areas of different character and shown to predict mean monthly SPM-concentrations in water and Secchi depth (a measure of water clarity) very well (generally within the uncertainty bands given by the empirical data). The model is based on processes regulating inflow, outflow and internal fluxes. The separation between the surface-water layer and the deep-water layer is not done in the traditional manner from water temperature data but from sedimentological criteria (from the wave base which regulates where wind/wave-induced resuspension occurs). The model calculates the primary production of SPM (within the coastal areas), resuspension, sedimentation, mixing, mineralization and retention of SPM. The SPMmodel is simple to apply in practice since all driving variables may be readily accessed from maps or regular monitoring programs. The model has also been extensively tested by means of sensitivity and uncertainty tests and the most important factor regulating model predictions of SPM-concentrations in coastal water is generally the value used for the SPM-concentration in the sea outside the given coastal area. The obligatory driving variables include four morphometric parameters (coastal area, section area, mean and maximum depth), latitude (to predict surface water and deep water temperatures, stratification and mixing), salinity, chlorophyll and the Secchi depth or SPM-concentration in the sea outside the given coastal area. Many of the structures in the model are general and could potentially be used for coastal areas other than those included in this study, e.g., for open coasts, estuaries or areas influenced by tidal variations.
Ocean Science Journal, 2011
The integration of remote sensing data of suspended particulate matter (SPM) into numerical models is useful to improve the understanding of the temporal and spatial behaviour of SPM in dynamic shelf seas. In this paper a generic method based on the Ensemble Kalman Filtering (EnKF) for assimilating remote sensing SPM data into a transport model is presented. The EnKF technique is used to assimilate SPM data of the North Sea retrieved from the MERIS sensor, into the computational water quality and sediment transport model, Delft3D-WAQ. The satellite data were processed with the HYDROPT algorithm that provides SPM concentrations and error information per pixel, which enables their use in data assimilation. The uncertainty of the transport model, expressed in the system noise covariance matrix, was quantified by means of a Monte Carlo approach. From a case study covering the first half of 2003, it is demonstrated that the MERIS observations and transport model application are sufficiently robust for a successful generic assimilation. The assimilation results provide a consistent description of the spatial-temporal variability of SPM in the southern North Sea and show a clear decrease of the model bias with respect to independent in-situ observations. This study also identifies some shortcomings in the assimilated results, such as over prediction of surface SPM concentrations in regions experiencing periods of rapid stratification/de-stratification. Overall this feasibility study leads to a range of suggestions for improving and enhancing the model, the observations and the assimilation scheme.
Estuarine, Coastal and Shelf Science, 2008
An algorithm is presented for estimating near-surface SPM concentrations in the turbid Case 2 waters of the southern North Sea. The single band algorithm, named POWERS, was derived by parameterising Gordon's approximation of the radiative transfer model with measurements of Belgian and Dutch inherent optical properties. The algorithm was used to calculate near-surface SPM concentration from 491 SeaWiFS datasets for 2001. It was shown to be a robust algorithm for estimating SPM in the southern North Sea. Regression of annual geometric mean SPM concentration derived from remote sensing (SPM rs ), against in situ (SPM is ) data from 19 Dutch monitoring stations was highly significant with an r 2 of 0.87. Further comparison and statistical testing against independent datasets for 2000 confirmed the consistency of this relationship. Moreover, time series of SPM rs concentrations derived from the POWERS algorithm, were shown to follow the same temporal trends as individual SPM is data recorded during 2001. Composites of annual, winter and summer SPM rs for 2001 highlight the three dominant water masses in the southern North Sea, as well as their winter-fall and spring-summer variability. The results indicate that wind induced wave action and mixing cause high surface SPM signals in winter in regions where the water column becomes well mixed, whereas in summer stratification leads to a lower SPM surface signal. The presented algorithm gives accurate near-surface SPM concentrations and could easily be adapted for other water masses and seas.
Journal of Geophysical Research, 2009
1] Accurate representation of light attenuation by inorganic suspended particulate matter (SPM) is one of the major factors limiting realism in coupled physical-biogeochemical models used to simulate primary production in shelf seas. The main problem is the accurate calculation of SPM concentrations. A multiple-grain size advection-diffusion method is presented, and results are compared to observations. The method has been incorporated in the 1-D hydrodynamics model General Ocean Turbulence Model. Particular attention has been given to the representation of sediment pickup, which is based on upward diffusion of sediment from a reference concentration near the seabed. Also, a bulk approach is used where the dominant fraction governs the pickup of the other fractions. A seabed model using the active layer approach is included. Moreover, to better represent seasonal cycles in background SPM concentration, a temperature-dependent kinematic viscosity is used, which modifies settling velocities and sediment pickup. Model results were tested against multiyear time series of surface observations of SPM using an Optical Backscatter sensor on ''SmartBuoy'' at two sites on the UK shelf and against suspended load observations obtained from Niskin bottle samples. It was found that at least four size fractions are required for reasonable predictions of the SPM concentration at the two sites: a coarse fraction representing the median grain size of the seabed sediments, two silt fractions responsible for most of the variability near the sea surface, and a clay fraction that provides a background concentration with slow variations in time. The method can easily be extended to 3-D models.
Continental Shelf Research, 2015
The objective of the study described in this paper is to localize the transport path of suspended particulate matter (SPM) in the Dutch coastal zone in the southern North Sea. It is known that a large mass of SPM is transported northward from the Strait of Dover, which is however mostly hidden from satellite and other surface measurements. The study area is located at 80 km north of the Rhine-Meuse estuary mouth in the far-field plume of the region of freshwater influence (ROFI). We investigate the occurrence and persistence of a turbidity maximum zone (TMZ) in an area closer to the coast than studied in previous observational programs. Shipboard measurements of vertical profiles of SPM concentrations, density and current velocities with a high cross-shore spatial resolution are presented. A turbidity maximum zone is found at a distance between 0.5 and 3 km from the coast along 30 km of the coastline. Observed concentrations are shown to vary strongly within a tidal cycle, and also between contrasting meteorological conditions in terms of the spring-neap tidal cycle, the significant wave height and the wind force. Temporary stratification is observed during spring tides, and occurs on the ebb phase of the tidal cycle. Cross-shore transports at a transect perpendicular to the coast show an accumulation of SPM in the TMZ within one tidal cycle. Possible mechanisms for this accumulation close to the coast are discussed.
Modelling SPM on the NW European shelf seas
Geological Society, London, Special Publications, 2007
The Proudman Oceanographic Laboratory Coastal Ocean Modelling System (POLCOMS) has been developed to tackle multidisciplinary studies in coastal/shelf environments. The central core is a sophisticated three-dimensional hydrodynamic model that provides realistic flow fields to interact with, and transport environmental parameters. The model uses realistic forcing with ocean currents and hydrography at the boundary, atmospheric forcing and tides.