Dynamics and properties of sands and suspended particulate matter (SPM) in the Conwy 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 (SSC) at the surface reached a maximum of
47mgl^-1. 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 flocs formed. At the 5 anchor stations, the total
cumulative flood flux (11 kgm-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 flocs (median
size 119 µm) of low density (82 kgm^-3 ) were observed with average surface SSC of 22 mgl^-1. In the estuarine turbidity maximum (ETM) region (mean salinity 5), the median floc size was 98 µm, while floc density increased to 135 kgm^-3, with
average surface SSC of 43 mgl^-1. In the lower estuary (mean salinity 27), the median floc size (114 µm) 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*1og(Q/T³). Similarly, SSC in the ETM was predicted by: log(SSC_ETM)=1.48+0.201 *(log(Q/T³))²+0.21 *log(Q/T³), where D (km) is the distance from the mouth, Q (m³s^-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 SSC 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 al., 2006) using the Conwy flow ratios. The Taf relationship underestimated the ETM location by c. 4 km. At very low flow ratios; the Taf SSC relationship overestimated the concentration by 200- 400 mgl^-1.
The estuarine sands, of modal grain size (180 µm), were made-up of 70 - 90% quartz particles. Mineralogical analysis showed that the provenance of the estuarine sands is Conwy 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 0.4-6.0 kgm^-1/survey, whilst total ebb transport was 0.1-2.2 kgm^-1/survey.