An analytical and experimental study regarding critical submergence for a 90° horizontal intake in an open channel flow, is presented in this paper. Based on the potential flow and critical spherical sink surface theories, an analytical equation for the critical submergence for this type of intake is derived using two different locations of intake from the channel bed – one with clearance from the bottom equal to zero and the other having half the intake diameter. Experiments were performed in a concrete flume 10m in length, 0.37m wide, and 0.6m deep, using intake pipes with diameters equal to 4.25mm, 6.25mm and 10.16mm for collecting data for critical submergence under a wide range of flow conditions. Analysis of this data reveals that the critical submergence depends on the Froude number, ratio of intake velocity and channel velocity, Reynolds number, and Weber number. However, the effect of the Froude number and the ratio of intake velocity and channel velocity is more pronounced in comparison to the other parameters. Based on the statistical analysis, predictors for critical submergence for bottom clearance equal to zero, and half of the diameter, are proposed and validated with the unused data. The proposed predictors produce satisfactory results. However, the analytical equation does not produce satisfactory results due to large boundary effects. It also does not take into account the effect of viscosity, surface tension, and circulation, in its derivation. The predictors available in the literature when examined using these data were found to overestimate the value of critical submergence.An analytical and experimental study regarding critical submergence for a 90° horizontal intake in an open channel flow, is presented in this paper. Based on the potential flow and critical spherical sink surface theories, an analytical equation for the critical submergence for this type of intake is derived using two different locations of intake from the channel bed – one with clearance from the bottom equal to zero and the other having half the intake diameter. Experiments were performed in a concrete flume 10m in length, 0.37m wide, and 0.6m deep, using intake pipes with diameters equal to 4.25mm, 6.25mm and 10.16mm for collecting data for critical submergence under a wide range of flow conditions. Analysis of this data reveals that the critical submergence depends on the Froude number, ratio of intake velocity and channel velocity, Reynolds number, and Weber number. However, the effect of the Froude number and the ratio of intake velocity and channel velocity is more pronounced in comparison to the other parameters. Based on the statistical analysis, predictors for critical submergence for bottom clearance equal to zero, and half of the diameter, are proposed and validated with the unused data. The proposed predictors produce satisfactory results. However, the analytical equation does not produce satisfactory results due to large boundary effects. It also does not take into account the effect of viscosity, surface tension, and circulation, in its derivation. The predictors available in the literature when examined using these data were found to overestimate the value of critical submergence.
