Giliomee, Thea Maria DorotheaLoots, IoneVan Dijk, Marco2026-03-022026-03-022026-02-15Giliomee, T.M.D., Loots, I. & Van Dijk, M. 2026,' Inlet modifications for increased box culvert capacity : a numerical modelling approach', Water Science and Technology, vol. 93, no. 4, pp. 469–482, doi : 10.2166/wst.2026.218.0273-1223 (print)1996-9732 (online)10.2166/wst.2026.218http://hdl.handle.net/2263/108700DATA AVAILABILITY STATEMENT : All relevant data are included in the paper..Inlet modifications applied to culverts can increase the culvert discharge capacity, which will help stormwater drainage systems adapt to larger flood events. Wingwalls and headwalls are already widely used as retaining structures. It is therefore feasible to optimise these inlet structures to increase culvert capacity. Building upon previous physical modelling research, this study evaluated a wider range of headwall and wingwall angle combinations to refine the findings. Headwalls and wingwalls were compared with rounded-edge box culvert inlets with the aim of improving capacity under inlet control. Numerical modelling was used to optimise wingwalls and headwalls and rounded-edge inlets, quantify their improvement, and verify the alignment of results with established references and guidelines. A 15° headwall with a 15° wingwall added to a box culvert improved the flow by up to 34% at a headwater depth of twice the culvert height (2D), or up to 26% at 1.2D. This solution provides the best balance between hydraulic performance and practical implementation. The largest improvement obtained by rounding the edges of a square box culvert is 30% at 2D. Inlet modifications provide a sustainable solution to increase culvert drainage capacity, which can mitigate flood risks. HIGHLIGHTS • Modified inlets can be used to adapt culverts to increased peak floods. • Numerical modelling presents an opportunity to test multiple combinations. • The smallest wingwall and headwall angles provide the greatest flow improvement. • Wingwalls and headwalls are more effective than rounded-edge inlets for box culverts. • Discharge capacity improvements were quantified for each inlet configuration.en© 2026 The Authors. This is an Open Access article distributed under the terms of the Creative Commons Attribution Licence (CC BY 4.0).Computational fluid dynamics (CFD)Stormwater drainageHydraulic structuresHydraulic capacityFlood controlArticle