Flow Hydraulics In An Ephemeral Gully System Under Different Slope Gradients, Rainfall Intensities And Inflow Conditions

Overland flow in an ephemeral gully (EG) system includes the EG channel, rill and interrill sheet flows, which comprise an interconnected drainage network. There are abundant researches on the hydraulics of rill flow and interrill sheet flow, as well as their relationships with soil detachment rates and sediment loads. Few studies have quantified the flow hydraulics of EG system which is highly related to the EG erosion and the development of better EG management strategies. Thus, two erosive rainfall intensities (50 and 100 mm h(-1)) and two slope gradients (15 degrees and 20 degrees) under different upslope and lateral inflow boundary conditions were employed to study the flow hydraulics of an EG system using simulated rainfall and inflow experiments. The results showed that flow velocity, shear stress, stream power and cross-sectional energy in the EG channel generally increased from the top to bottom of the slope with different trends and fluctuations under various inflow conditions. The flow hydraulic parameters of EG channel, rill, and interrill sheet flows all increased as rainfall intensity and slope increased. Flow regimes in the EG system were divided based upon the Reynolds number and Froude number. EG channel flow was classified as transitional to turbulent flow, rill flow was transitional, while sheet flows on interrill areas was laminar. From sheet flow to rill flow and EG channel flow, the flow regime gradually shifted from laminar and subcritical flow to turbulent and supercritical flow. The flow force, power and energy correspondingly increase as flow regime changed toward turbulent and supercritical. Good relationships between sediment load and flow hydraulic parameters were observed and flow shear stress was found to be best correlated with soil erosion of the EG system (R-2 = 0.92). This study quantitively mapped the flow hydraulics in the EG system and correlated these with erosion features, contributing to the development of process-based EG prediction models and better EG management strategies.