Development of a model to reproduce observed suspended sediment distributions in the southern North Sea using Principal Component Analysis and Multiple Linear Regression

Abstract

As part of the NERC North Sea Project (1987–1992), concentrations of fine suspended particulate matter were determined at over 100 locations on 15 monthly survey cruises. Each of these monthly data sets were interpolated to provide continuous “synoptic” representations over the southern North Sea (south of 56°N). Here, statistical techniques are used in conjunction with numerical model simulations to interpret these data. Principal Component Analysis is performed on these monthly series of observations to locate statistically significant sources and sinks of suspended particulate matter. This analysis reveals the month-to-month variability of a primary source, accounting for around 80% of the total variation in the observations, and located in the vicinity of The Wash estuary and adjacent coast. A numerical dispersion model is then developed to simulate the erosion, settling and transport of fine suspended sediment from this source. The formulations and associated coefficients used to describe re-erosion and settling rates are then fine-tuned by comparison with observations. In the second part of this study, the sediment model developed is used to simulate dispersion from discrete sources. Thence a Multiple Linear Regression technique, as described by McManus and Prandle (1994) (in Marine Pollution Bulletin 28, 451–455), is used to fit these modelled dispersion patterns to the original observations to determine rates of sediment supply from these discrete sources. This technique reveals that (i) riverine sources are not statistically significant and (ii) the East Anglian sources are small in magnitude compared with the Dover Strait and northern North Sea sources. Further analysis explains this apparent contradiction with the first part of the study by illustrating how the longer effective flushing times of the two coastal sources amplifies their net contribution to the suspended particulate matter distribution in the southern North Sea. Estimates of mean annual supply from the statistically significant sources (in 10 6 t) are Dover Strait, 44.4, northern North Sea, 41.7, The Wash, 3.2, and Suffolk Coast, 0.7. Comparable estimates published in the 1993 North Sea Quality Status Report (North Sea Task Force, Olsen and Olsen, Denmark) are generally in reasonable agreement. Likewise, both the location and rates of supply from the sources determined in this study are in broad agreement with the earlier estimates of McCave (1987) (in Journal of the Geological Society 144, 149–152). Thus, the success achieved provides encouragement towards the goal of developing robust suspended sediment models of shelf seas.