Estimation method of water surface profile in the stepped geobag spillway chute considering the aerated flow

Check dams are a cornerstone soil and water conservation measure on the Loess Plateau, providing siltation, erosion control, and ecological benefits. However, recent extreme rainfall events and structural deterioration have increased the risk of dam failures. The stepped flexible spillway technology developed by Chen's team offers a robust solution to mitigate these risks. Yet, the complex hydrodynamics of such spillways, particularly the significant effects of air entrainment, are not adequately addressed in current design codes. In response, this study establishes a relationship between Darcy's friction factor and surface roughness based on published laboratory test data. It further proposes a water surface profile calculation method that accounts for aerated flow under varying weir head conditions. This methodology provides a valuable reference for designing stepped flexible spillways and supports the broader application of this technology in dam rehabilitation and safety enhancement projects.