Disrupted sediment pathways and coastal erosion governance: Integrating riverine dynamics and livelihood-dependent community perception along Sri Lanka’s southwestern coast

Abstract

Coastal erosion along river-influenced shorelines results from complex interactions between altered sediment dynamics and human interventions, yet management strategies often rely on fragmented physical or social assessments. This study investigates coastal erosion along the Bentota-Colombo Port City coastline in Southwest Sri Lanka by integrating empirical sediment transport analysis of the Kalu River system with an assessment of coastal stakeholder perceptions. Sediment transport patterns were analysed to quantify changes in river-coast connectivity, particularly following the 2017 estuarine modification, while community perceptions were evaluated using structured surveys and stakeholder engagement across multiple coastal user groups. Results indicate that riverine and estuarine modifications have altered sediment flux pathways, contributing to sediment deficits along adjacent beaches and exacerbating shoreline instability. Conversely, stakeholder perceptions of erosion drivers are primarily shaped by visible coastal interventions, such as hard engineering structures and large-scale developments, while upstream sediment processes remain underrecognized. This mismatch between measured sediment dynamics and public understanding influences management preferences, often favouring reactive, site-specific engineering solutions over holistic strategies. By linking physical sediment evidence with community perceptions, the study demonstrates how gaps between scientific knowledge and social interpretation can undermine the effectiveness and legitimacy of coastal management interventions. The findings emphasize the need for integrated, source-to-sink governance approaches that align sediment management strategies with stakeholder awareness and participation. This framework provides actionable insights for erosion management in monsoon-dominated, data-limited coastal systems undergoing rapid development.