Bulletin of the Geological Society of Denmark, Vol. 27/01-02, pp. 15-45

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20 Nielsen & Nielsen: Nearshore sediments in non-tidal environment Fig. 7. The mean grain sizes (MJ and sorting (6,) (Folk & Ward 1957), shown in relation to the most important morphological borders. no line , Q 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50 52 1.81 0.42 1.94 0.44 1.00 1.2! 1.88 0.95 2.20 0.4$ 2.00 0.5! 2.17 0.5! 2.35 0.50 2.44 0.42 2.61 0.38 2.52 0.46 2.40 0.41 2.41 0.30 2.36 0.42 2.39 0.38 2.34 0.41 2.31 0.39 2.43 0.37 2.44 0.29 2.51 0.32 2.64 0.34 2.54 0.5! backshore foreshore nearshore terrace nearshore bar J front 2.57 2.66 0.42 0.42 / \ 1 1.71 0.50 1.74 0.75 2.58 0.59 2.61 0.44 2.01 0.53 V 2.30 0.44 I I" 48 ' \^0.4S 2.68 0.38 2.30 0.39 2.44 0.3! 2.71 0.35 2.44 0.46 Mz Æ, ° i 10 11 12 13 2. .06 _ /o .34 ^ ^ \ ' 2 .22 ^ \ 0, .40 2, .26 0. .35 2, .26 0. .41 2, .45 0. .36 2. .50 0. .35 2. .32 0. , 4 , x 2. .47 2.68 0. .32 0.38 1.87 0. 38 1.83 0.43 0.89 1.62 0.79 1.34 2.15 0.4$ 2.17 0.55 2.38 0.4% 2.49 \ 0 . 4 2 2.13 0.49 2.32 0.43 2.42. 0.43 2.48 0.37 2.29 0.50 •2.28 0.44 2.38 0.44 2.38 0.43 2.40 0.38 2.42 0.38 2.60 0.28 2.62 0.3! 2.69 0.30 2.70 0.36 due the water column. Unfortunately, we did not have a recorder at our disposal, so wave heights had to be found by means of the waterlevel board, and wave period and -length had to be measured within the pole net. Compared with the quality of the measurements of form elements, we consider those of waves as a weak link in the present work. To illustrate the sediment conditions of the locality, samplings by a 5 cm high aluminium cylinder (diameter 4.5 cm) were made at each pole in lines 1 and 13, and at each second pole in line 7 and in crossline 52 (60 samples). Besides this sampling, which gave a general picture of the grain size distribution of the area, a detailed sampling (29 samples) was made in line 9 across a nearshore bar. Sediments in the study area Besides showing a slight difference between the most important morphological zones (backshore, foreshore, nearshore) the statistical parametres demonstrate a homogeneous sediment in the investigation area (fig. 7). A more detailed statistical analysis was therefore only made for the special sampling in line 9 in order to trace possible sorting processes in connection with the formation and migration of the nearshore bar. Because of the slight variations an F-test was made by pairwise comparison, to investigate whether the sorting of the samples was significantly different. This was only due for combinations of samples from the top of the bar and from the seaward trough; but neighbour samples might mutually originate from the same mother distribution. Where the F-test allowed, at-test was made on the mean grain size. By means of the t-tests' significance levels, it was now possible to separate 3 sediment types. For each group, a weighted average was calculated (fig. 8). The largest mean grain size was found on the upper part of the flat stoss side of the nearshore bar, the side most exposed to the dynamic forces.
Bulletin of the Geological Society of Denmark, vol. 27 1978 21 JERSIE STRAND, KØGE BUGT Type of sediments of the nearshore bar Profile 9 surface morphologi type of sediment ripples M- > 2.27 I 2.12 I 207 ' 230 ' smooth 2.27 207 ripples Oct. 6 th. 1971 asym symmetrical 2.46 181 smooth bottom I 2.27 207 20 metres Exaggeration- 112.5 x Fig. 8. Relationship between grain size parameters, morphology ments were taken at a quite smooth bottom influenced by surf and bedforms on the nearshore bar in line 9. waves, whereas the fine-grained sediments were found in places During the sampling, variations in the micro morphology of with ripples formed by the oscillating waves. the sea bottom were ascertained. The most coarse-grained sedi The grain size is decreasing both on the leeside and down towards the runnel in front of the next nearshore bar, a pattern which could also be discerned in the general sampling. Morphological development during the observation period The general morphological development in the study area appears from the selected contour maps (figs 9a-j). The nearshore bar migrates onshore at varying speeds, but stagnates before it reaches a complete fusion with the foreshore (16/10, fig. 9g), partly because new bars, formed seaward of the old one, absorb a great deal of the wave energy (fig. 11). A characteristic feature in the development of the nearshore bar is that it does not migrate at right angles onshore, but obliquely through the study area. During the last part of the investigation period (4/11 to 11/11, figs 9i-j), the nearshore bar is dissolving just as it leaves the study area. For more detailed analyses of the morphological development there was constructed besides the contour maps, a map showing the movements of the bar fronts and the swash bars (fig. 12) and a timedistance diagram of the profile lines 1,4, 7, 10 and 13. The T-D diagram makes it possible to correlate the about 20,000 level records from the 65 contour maps and follow the morphological development in connection with wind- and water level observations (figs lOa-c). There were made no statistical levellings of the recorded wind- and water-level data such as Fourier analyses, as suggested by Davis and Fox 1971 and 1972 because the alterations of form on the beach plane terrace take place during specific weather situations and within very short intervals.
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Bulletin of the Geological Society of Denmark, Vol. 27/01-02, pp. 15-45

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