An experimental study of flow into orifices and grating inlets on streets

Findings are described from a laboratory-scale model of flow through orifices on manhole covers and through three types of grating inlets used by the City of Edmonton. The results demonstrated that the flow through these orifices can be calculated using an orifice equation with a coefficient of discharge equal to 0.616 in a ponding situation but decreasing with an increase in the Froude number of the flow. The roughness of the manhole cover was found to slow down this reduction. For the three gratings, the inflow can be calculated with an orifice type of equation when the gratings are submerged. The discharge coefficient in this equation is approximately constant for two of the gratings and decreases somewhat with an increase in the Froude number of the flow for the third grating if the specific energy of the approaching flow is used as the length scale. © 2006 NRC Canada.