The risk of flooding associated with blockage of culverts by natural and anthropogenic debris is often reduced by fitting a trash screen at the structure's inlet. However, screens can actually exacerbate flood risk if not properly designed and maintained. In this paper, findings from a project that has been tasked with developing decision support tools to help the asset manager prioritise screen clearance strategies are explored. The scientific knowledge base surrounding this complex issue has been extended using an empirical approach by correlating the probability of delivery of significant debris loads to trash screens, as determined using data from 140 screen sites in Belfast, Northern Ireland, with pertinent driving variables including channel properties, flows, land use types and the degree of social deprivation. This analysis has enabled fundamental relationships to be developed that, once validated, will help planners to establish the potential loads of debris that may be delivered to screens and will therefore offer a robust means to rank culverts in terms of blockage potential and therefore flood risk.