Designing Verifiable Educational Simulations: Technical Verification of OpenHydroLab for Undergraduate Hydraulics and Hydrology

Interactive simulations can help students explore relationships that static figures cannot show easily. Their educational value, however, depends on a basic condition: the simulation must compute and display what it claims. This study presents OpenHydroLab, an open-source suite of ten browser-based laboratories for undergraduate fluid mechanics, hydraulics, and hydrology. It also develops a reproducible protocol for verifying the implementation. The protocol combines independently derived reference solutions with explicit tolerances and parameter sweeps. It also tests rendered geometry, browser behaviour, offline delivery, and selected accessibility requirements. In total, 197 numerical cases were evaluated in three browser engines, producing 591 comparison records. A further 108 software and accessibility checks were executed 324 times. No failures remained in the final verification run. The protocol identified six defects in code that had already been used in teaching. A seventh defect passed the numerical checks but drew a correct force magnitude on the wrong side of a curved surface. This showed why visual claims must also be tested. OpenHydroLab therefore provides a worked example of how educational simulations can be made inspectable, reproducible, and technically trustworthy. More broadly, effective technology integration in STEM education requires more than access to interactive tools. It also requires transparent evidence that their computational and visual representations can be trusted. The study establishes implementation fidelity and delivery reliability; it does not evaluate learning effectiveness.