Inlet modifications for increased box culvert capacity: a numerical modelling approach

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.