Development of an Aqueduct Flow and Ice Simulation Model

The Fargo-Moorhead Metropolitan Area Flood Risk Management Project, located at Fargo, ND, and Morehead, MN, is to include an aqueduct to carry the flow of the Maple River over a proposed diversion channel. The aqueduct is 250 ft long with an internal width of 50 ft. A V-shaped low-flow channel is built into the floor slab at the center of the channel and is 12 ft wide. The aqueduct will operate throughout the winter when frigid conditions will cause ice to form. This study quantified the amount of ice that forms in the aqueduct under different winter operating scenarios. To achieve this, the study developed an aqueduct flow and ice simulation model composed of five modules. These modules determine the water surface profile through the aqueduct, the water temperature resulting from the interaction of proposed bed heaters and the surface ice conditions, the formation of bed ice by heat conduction through the aqueduct to the outside air, the formation of surface ice through heat transfer from the water surface to the atmosphere, and the interaction of the bed and surface ice.In addition, a HEC-RAS and a finite-element thermal conduction model of the aqueduct were used. The HEC-RAS model was used to determine the aqueduct’s downstream water surface elevation boundary condition. We also used the HEC-RAS model to verify the open water flow estimation of the aqueduct model. We used the finite-element thermal conduction model to develop a 2-D simulation of the thermal conduction through the aqueduct cross section. The thermal conduction model allowed us to analyze the heat flow through the aqueduct structure under different flow conditions, heating elements applications, and thermal insulation applications. The model simulated flow through the aqueduct based on the conditions for each day for the winters of 1995 to 2013 for a variety of operating scenarios.