<p>The study of channel behaviour is significant in the design of an underwater acoustic (UWA) communication system. In a time-varying underwater environment, transmitted acoustic signal characteristics might be altered due to the impact of scatterers. To examine the impact, this work presents geometry-based modelling of UWA channels for a mobile receiver under different scattering conditions. The model considers scattering from the sea-surface, seabed, and both sea-boundaries, incorporating uniform and random distributions of scatterers to represent underwater propagation conditions. A total of 21 scenarios were analysed to evaluate the combined influence of transmitter–receiver geometry, scatterer distribution, and receiver mobility on UWA channel characteristics. The analysis was carried out using channel impulse response, temporal correlation, received power, and RMS delay spread metrics. The simulation results show that the configuration with the transmitter located below the receiver generally provides more favourable propagation characteristics, with comparatively higher received power and lower multipath dispersion, followed by the configurations with the transmitter located inline and above the receiver. Seabed scattering environments exhibit stronger attenuation and larger delay spread, while surface scattering has the least impact. The findings demonstrate that transmitter–receiver geometry and scatterer boundary conditions significantly influence channel stability and multipath behaviour in UWA communication environments.</p>