Suspended sediment fluxes in the tidal Ouse, UK

Abstract

A strong turbidity maximum (TM) of suspended particulate matter (SPM) was observed in the upper Humber and lower Ouse during both spring and neap tides of May 1994. Near-bed concentrations within the TM sometimes exceeded fluid mud levels following slack water periods. SPM within the TM comprised very fine-grained material. Its low organic content demonstrated that the SPM was essentially mineral, clastic sediment. Generally, tidal advection of SPM was the dominant flux mechanism and the pronounced flood-ebb asymmetry in the tidal currents was reflected in these fluxes. However, the presence of fluid mud near the down-estuary margins of the TM on the early ebb resulted in a strong, up-estuary shear flux that opposed the ebb-directed advection. This mechanism therefore acted to maintain fine sediment in the TM region. SPM concentrations in the inflowing fresh water at Naburn Weir were much less than those observed within the TM region ( 70 000 mg l -1 ). The estimated mean SPM transport into the tidal Ouse across Naburn Weir was about 4 kg s -1 (>2 and <11 kg s -1 ) during 1994. In the TM area, the SPM transported during the course of a single spring tide flood was roughly equivalent to 30 months of Naburn SPM inflows at average 1994 levels. The tidally averaged SPM transport in the TM region was directed into the estuary and, per tide, was roughly equivalent to three months of Naburn inputs.