Improving Hydraulic Capacity with Inlet Modifications to Box Culverts using Numerical Modelling

Abstract

Culverts can become inadequate over time due to increasing flood peaks caused by higher-intensity rainfall events and urban development. Modifying the culvert inlet to increase discharge capacity can negate the need to rebuild the entire structure. Using Cradle CFD scFLOW Hexagon software for numerical modelling, this study found that box culverts with a 15° headwall and 15° wingwall increased the flow capacity by up to 34% at a headwater depth of twice the culvert opening (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%. A new flow improvement coefficient, CTG, is proposed to quantify the improvement for each type of inlet, which can be used with existing design equations to calculate the improved discharge capacity for specific inlet modifications. Implementing inlet improvements for new and existing culverts will reduce flood risks and contribute to the climate resilience of road infrastructure.