A suspended sediment transport model was set up for Ōhiwa Harbour, which was validated against in situ observations collected between 19/4/21 and 17/5/21. Four sediment grain size fractions were modelled; two cohesive (silt) sediment grain size fractions, and two non-cohesive (sand) sediment grain size fractions. Characteristics of these grain size fractions were selected based on a sensitivity analysis and the match of modelled suspended sediment to the magnitude and temporal patterns recorded at the observation stations. Suspended non-cohesive grain size fractions reflect local current strengths at the sites measured, whereas cohesive grain size fractions are advected longer distances by the ebbing or flooding currents. Sediment loading was input at the freshwater discharge points using loading scenarios provided by the Bay of Plenty Regional Council. Sediment loading was converted to a concentration and discharge, and input into the model as a cohesive sediment grain size fraction. Model scenarios were run for 1 year in blocks of 3 months, using the environmental conditions (discharge, wind, tides) from 2014 as a base-case scenario. Loading scenarios consisted of contemporary, natural, RCP45 and RCP85 conditions. A 7-day model “warm up” period prior to each of the 3-month blocks was discarded.