The Threshold Concept Framework is used to initiate a dialogue on an empirically supported pedagogy that focuses on students' conceptual understanding required for solving application-based problems. The present paper uses a triangulation approach to identify the threshold concept in a third-year undergraduate civil engineering course on open channel hydraulics. Evidence from teachers, students, and assessment data point to "critical flow" as the threshold concept--a concept that is transformative, integrative, and troublesome. Identifying the threshold concept by engaging various course stakeholders in a dialogue about conceptual understanding and capabilities makes learning visible for all participants in the process. Implementing this approach can result in an empirically driven rationale for adjusting pedagogies and assessments to foster enhanced student learning outcomes.