Abstract: Stable hydraulic jump is a typical flow regime in discontinuous density current, which switches the flow from supercritical to subcritical. It usually features energy consumption and entrainment, but previous research lacks a good explanation of the corresponding relationship between the both processes. In this study, the hydraulic jumps of sediment density current are observed in a flume experiment, and their energy consumption and local entrainment are examined by deriving a head loss formula. We find that an increase in sediment concentration or initial water depth at the inlet or a decrease in inlet velocity will lead to the weakening of the jump and a decrease in conjugate depth ratio. And the increase in density current layer thickness will be more limited. Such inlet flow changes will also lead to less head loss, a reduced volume of clear water entrained from the upper layer, and a reduced density of the turbid layer. An analysis of the energy consumption process of the jump reveals that the decrease in energy consumption indicates the weakened turbulence intensity near the interface of the two flow layers, thereby effectively reducing the entrainment from the upper layer. Using regression analysis, we find that either conjugate depth ratio versus head loss ratio ?hf/hf1 or ?hf/hf1 versus entrainment coefficient KQ shows a positive linear relationship. The energy index derived in this paper is a feasible method to analyze the hydraulic jumps of density current and reveal their local entrainment mechanism.

Key words: sediment density current, stable hydraulic jump, conjugate depth, head loss, local entrainment