Circulation and mixing in estuary outflows |
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| Authors: | RE Lewis |
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| Institution: | 1. ICI plc., Brixham Laboratory, Brixham, Devon |
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| Abstract: | The outflow of brackish waters from the Tees estuary on an ebb tide forms a plume which is initially spread by the action of gravity. Under quiescent conditions, the rate of vertical mixing of the brackish field is relatively slow and an area of low salinity may form in the surface waters as a result of the superimposition of the outflow plumes from successive tides. A field area of some 70 km2 has been observed to be enclosed by the 34.2 × 10?3 contour.Averaged over a tidal period, the estuary outflow from the Tees forms a broad plume of low-salinity water which extends to seaward of the 20-m contour. The movement of the field thereafter depends on the residual coastal drift which runs either to the northwest or to the southeast with a typical speed of 0.015 m s?1. The tidally averaged vertical mixing coefficient in this offshore field was estimated to be about 10?4 m?2 s?1, which is similar to that off the Wear estuary and an order of magnitude smaller than that calculated for the waters off the Humber. |
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