Linear Erosional Furrows in Southampton Water

Abstract

THE floor of the lower part of the estuary of Southampton Water (Fig. 1) has been examined with a Kelvin Hughes MS 43 transit sonar and an MS 36 echo sounder¹. Upstream of Fawley the almost central deep channel is maintained by dredging to a least depth at low tide of about 11 m. On the western side the slope is a steady 1°–2°, but on the eastern side there is a wide shelf at about 2 m below port datum. To the seaward of Fawley there is a natural depth of 14 m below port datum. The sea bed consists of a soft mud made up of flocculated clay and fine silt particles. The flocculants have an equivalent mean grain size of about 5.5 Φ (22 µm). The mud is comparable with other marine muds having a moisture content of 120–220 per cent dry weight and a surface cohesion between 4–2 g cm⁻². Occasional shell banks and gravel patches exist, especially near Calshot and on the eastern side.