Discharge ratings for control gates at Mississippi River Lock and Dam 11, Dubuque, Iowa

The water level of the navigation pools on the Mississippi River are maintained by the operation of tainter and roller gates at locks and dams. Discharge ratings for the gates on Lock and Dam 11, Dubuque, Iowa, were developed from current-meter discharge measurements made in the forebays. Methodology is given to accurately compute the vertical gate openings of the tainter gates. Discharge coeffients, in equations that express discharge as a function of tailwater depth, headwater depth, and vertical height of gate opening, were determined for conditions of submerged-orifice and free-weir flow. A comparison of the rating discharges to the theoretical rating discharges is given for submerged orifice flow for the tainter and roller gates.