Suspended sediment fluxes in the tidal Ouse, UK

A strong turbidity maximum (TM) of suspended particulate matter (SPM) was o bserved in the upper Humber and lower Ouse during both spring and neap tide s of May 1994. Near-bed concentrations within the TM sometimes exceeded flu id mud levels following slack water periods. SPM within the TM comprised ve ry fine-grained material. Its low organic content demonstrated that the SPM was essentially mineral, elastic sediment. Generally, tidal advection of S PM was the dominant flux mechanism and the pronounced flood-ebb asymmetry i n the tidal currents was reflected in these fluxes. However, the presence o f fluid mud near the down-estuary margins of the TM on the early ebb result ed in a strong, up-estuary shear flux that opposed the ebb-directed advecti on. This mechanism therefore acted to maintain fine Sediment in the TM regi on. SPM concentrations in the inflowing fresh water at Naburn Weir were muc h less than those observed within the TM region (<300 mg l(-1) compared wit h >70 000 mg l(-1)). The estimated mean SPM transport into the tidal Ouse a cross Naburn Weir was about 4 kg s(-1) (>2 and <11 kg s(-1)) during 1994. I n the TM area, the SPM transported during the course of a single spring tid e flood was roughly equivalent to 30 months of Naburn SPM inflows at averag e 1994 levels. The tidally averaged SPM transport in the TM region was dire cted into the estuary and, per tide, was roughly equivalent to three months of Naburn inputs. Copyright (C) 1999 John Wiley & Sons, Ltd.