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Title: Dynamics of sands and suspended particulate matter in the macrotidal Conwy Estuary, North Wales, U.K.
Author: Missias, Stefanos
ISNI:       0000 0001 3411 1540
Awarding Body: University of Wales (Bangor)
Current Institution: Bangor University
Date of Award: 2007
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Dynamics and properties of sands and suspended particulate matter (SPM) in the Gonwy Estuary were investigated. SPM properties were measured at specific locations over tidal cycles. Floc formation was restricted by increased turbulence at 3 h before low water (LW). At LW, decreased velocities allowed floc formation and partial sedimentation of SPM. At peak velocities c.3h after LW, the mean suspended sediment concentration (SSG) at the surface reached a maximum of 47mgr1 . Particle size increased and effective density decreased due to resuspension of low density, large particles. At high water slack (HW) when turbulence was a minimum, larger floes formed. At the 5 anchor stations, the total cumulative flood flux (11kgm-1) was twice the total cumulative ebb flux (5 kgm-1 ). SPM properties (of surface waters) were measured along the longitudinal axis of the estuary at HW. In the upper estuary (mean salinity 0), large floes (median size 119 IJm) of low density (82 kgm-3 ) were observed with average surface SSG of 22 mgr1 Â? In the estuarine turbidity maximum (ETM) region (mean salinitr 5), the median floc size was 98 IJm, while floc density increased to 135 kgm- , with average surface SSG of 43 mgr1 Â? In the lower estuary (mean salinity 27), the median floc size (114 IJm) was similar to that in the upper estuary, but with twice the floc density (159 kgm-3 ). At HW, the ETM occurred between 8 and 19 km from the mouth. It was found that the controlling factor of ETM location changed with the season and its SPM properties followed a seasonal cyclic pattern. ETM location varied with the flow ratio (river discharge / tidal range3); ETM location was predicted by: log(D)=0.997 -0.103*log(QIT3). Similarly, SSG in the ETM was predicted by: 10g(SSGETM)= 1.48+0.201 *(log~QIT3))2+0.21 *log(QIT\ where D (km) is the distance from the mouth, Q (m S-1) is river discharge, and T (m) is tidal range. The relationship placed the predicted ETM between 10 and 16 km from the mouth. The estimated depth average SSG in the ETM, agreed well with observed values. After modifying these relationships for summer conditions only, they were compared with ones produced for the Taf estuary (Jago et aI., 2006) using the Gonwy flow ratios. The Taf relationship underestimated the ETM location by c. 4 km. At very low flow ratios; the Taf SSG relationship overestimated the concentration by 200 - 400 mgr1 . The estuarine sands, of modal grain size (180 Ilm), were made-up of 70 90% quartz particles. Mineralogical analysis showed that the provenance of the estuarine sands is Gonwy Bay. Net transport paths of the estuarine sands were defined by analysis of the spatial variation of grain size characteristics; the overall sand transport was found to be in the up-estuary direction. Thresholds of motion and suspension for the estuarine sands were established for each of the 5 anchor stations, and sediment transport rates (bed and suspended loads) were calculated. The total flood transport was 0.46.0 kgm-1/survey, whilst total ebb transport was 0.1-2.2 kgm-1/survey.
Supervisor: Not available Sponsor: Not available
Qualification Name: University of Wales (Bangor), 2007 Qualification Level: Doctoral
EThOS ID:  DOI: Not available