Increasing culvert hydraulic capacity for improved climate resilience: a physical modelling analysis

Abstract

Culverts often fail to handle increased flood peaks due to urbanisation and climate change. Modifying culvert inlets to increase discharge capacity can negate the need for additional culvert barrels or to rebuild the entire structure. Although some previous studies investigated hydraulic culvert improvements, this study is the first to test different combinations of headwall and wingwall angles, and the effect of aeration vents, to improve capacity of inlet-controlled culverts. This physical modelling study evaluates various modified box and circular culvert inlets, quantifies their impact on capacity, develops a coefficient for use in standard equations, and verifies the alignment of results with established references and guidelines. A 15° headwall with a 30° wingwall added to a box culvert or a rounded inlet edge for a circular culvert improved the flow by up to 34% at a headwater depth of twice the culvert height (2D), or up to 18% at 1.2D for box culverts and 24% at 1.2D for circular culverts. An air vent after the inlet had an insignificant influence on the capacity. A novel flow improvement coefficient was developed to calculate improved capacity with existing design equations. Culvert inlet improvements will reduce flood risks and contribute to sustainable drainage infrastructure.