A pipe-based, first approach to modeling closed conduit flow in caves

Abstract

A closed conduit model is constructed for a discrete cave segment using the energy equation and the assumption that energy losses in the segment are generated by large-scale flow separation associated with expansions and bends. As employed, the model uses paleostage indicators and passage geometry to estimate total head loss across the study reach. Channel roughness is estimated using pipe-based equations and a skin friction factor estimated from secondary means. Discharge is varied in the model until calculated head loss matches observed head loss. The model is employed to estimate discharge for a flood recorded in Buckeye Creek Cave, West Virginia as high water marks consisting of silt lines. Under varying assumptions, the model yields paleodischarges in the range of 22–29 m 3 s −1. Shear stress values calculated using model output are in general agreement with the size distribution of gravel on the stream bed and shear stress values are relatively insensitive to changes in discharge. The apparent friction factor for the study reach is estimated to be in the range of 0.4–0.7, which is in general agreement with previous studies of large conduits. The model is applicable to similar cave reaches, but requires further testing and validation because so little is known about conduit flow in karst.