Small mountainous rivers deliver considerable sediment loading to the coastal ocean and play a disproportionate role in marine sediment deposition globally. Discharge in these rivers is often driven by short episodic events and they typically deliver sediment to energetic coastal environments where in-situ observations of cross-shelf sediment transport are spatially limited and are difficult to maintain over representative periods of time. How these river plumes respond to environmental conditions, and where sediment is initially deposited from the river plumes are essential to understanding long-term sediment transport and deposition patterns in the coastal ocean. This thesis explores this problem using three approaches applied to Hawke Bay (Aotearoa New Zealand) and its river plumes: remote sensing (paper 1), large-scale numerical modelling (paper 2) and high resolution in situ observations at one of the river mouths (the Tukituki River) (paper 3).