Effective management of sediment sources in coastal catchments requires a spatially explicit understanding of erosion processes and cost-effective management prioritisation. This study develops a catchment-scale decision support framework for the Richmond River catchment in northern New South Wales, Australia, to guide investment in riparian rehabilitation aimed at reducing sediment delivery to the estuary. High-resolution datasets were compiled for the entire 3rd-order-and-above channel network (1,442 km) and divided into 2,884 management reaches of 500 m. Multi-temporal LiDAR differencing (2010–2023) quantified channel erosion volumes, while 2023 LiDAR foliage projected cover mapping and Landsat-derived 35 year vegetation trends characterised riparian condition. These datasets were integrated with cost estimates for revegetation, weed control, fencing and assisted regeneration to construct a geo-economic prioritisation model. Marxan optimisation was applied to identify the least-cost combinations of reaches required to meet defined erosion reduction targets. Results indicate channel erosion is a dominant sediment source to the Richmond estuary, with total detected erosion of 3.28 million m³ and an estimated annual sediment yield of ~734,000 t. Full rehabilitation of the mapped network would cost approximately $336M, averaging $102 per m³ of erosion. Optimisation demonstrates strong economic leverage: treating 10% of total erosion requires rehabilitation of only 6.1% of reaches at 1.9% of total cost ($19.5/m³). Priority reaches are concentrated in upper catchment areas and largely outside the coastal zone, highlighting the importance of upstream management for estuary health outcomes. The framework provides transparency for catchment investment and riparian rehabilitation planning, but could be further improved with sediment tracing.