Steady Flow through Gated Circular Culverts: Hydraulic Operation and Experiments

Abstract

Culverts are ubiquitous hydraulic structures used in cross-drainage and agricultural water systems, especially at farm outlets in irrigation systems. Gate control adds hydraulic complexity to culvert water flow, yet it has hardly been studied. This study has two objectives: (1) to classify the operational conditions of gated culverts, and (2) to establish an experimental data set for analyzing discharge relationships based on that classification. A theoretical inlet–outlet control–based classification resulted in 22 inlet control and 19 outlet control cases, organized in 4 inlet and 5 outlet control groups. A total of 230 laboratory tests were conducted. The laboratory setup reproduced the conditions of inlet submerged with outlet in free surface (one of four inlet control groups) and all conditions except inlet in free surface with outlet submerged (four of five outlet control groups) of the inlet and outlet control groups, respectively. Comparison with existing classification schemes for gated culverts confirmed the suitability of the proposed scheme and provided further insight into flow classification. The discharge grouped by narrow ranges of gate openings was found to follow a power-law relationship of head with an exponent between 0 and 1. Flow transition regions between groups of conditions were examined, suggesting parabolic transition curves. The gate opening was found to be the dominant variable, resulting in a direct proportional effect on discharge, i.e., data corresponding to greater gate openings enveloped those with smaller openings. The slope’s influence could not be discerned within the slope range tested. Discharge estimation based on a dimensionless, empirical model produced reasonable results, although its case-dependent nature requires further research to develop operational hydraulic models for determining discharge through gated culverts. Application of the proposed classification scheme could help develop these hydraulic tools with sufficient accuracy.