Hydraulic Characteristics of a Drop Square Manhole with a Downstream Control Gate

Manhole drops in drainage systems are often designed for providing energy dissipation, for controlling high velocities and for minimizing sewers structural damage. The flow is characterized by excessive air-entrainment and high turbulence. The manhole geometry, the upstream and downstream flow characteristics and possible transitions between the manhole and the sewers control the flow inside the manhole. This experimental research aims to investigate the effects of a free jet in a square drop manhole with a downstream control gate by analyzing the flow conditions, discharge coefficients, turbulence downstream, and energy dissipation for three different flow regimes, R1, R2, and R3. This research propose to (1) adjust the limits of the existing regimes classification by including a new impact number based on downstream gate opening, and (2) obtain empirical equations for predicting the discharge coefficients with the flow regime. Non dimensional discharges were better predicted for R1 by using critical velocity. The energy dissipation and turbulence was found to respectively decrease and increase by raising the water discharge from the inlet and by opening the gate. DOI: 10.1061/(ASCE)IR.1943-4774.0000437. (C) 2012 American Society of Civil Engineers.