Thermally Induced Density Currents in Nonrectangular Sidearms

Steady‐state experiments in a dead‐end laboratory channel having an overbank cross section are used to investigate the effects of cross‐sectional shape on thermally induced gravitational circulation in cooling pond sidearms with large length‐to‐depth ratios. When the water depth is large over the overbank section, the flow is predominantly two‐dimensional, longitudinal, and located across the entire channel width above the level of the overbank section. As the water depth is decreased, both transverse shear and density driven cross‐channel circulation are observed. For very shallow water depths over the overbank section, the longitudinal circulation returns to two‐dimensional circulation, although it is located only in the deep part of the cross section. Comparisons to two‐dimensional theory quantitatively confirm the two‐dimensional behavior at the deepest water depth and show that even at very shallow water depths the overbank section remains quite effective for heat loss. An equivalent rectangular cross section can be defined for a nonrectangular cross section which allows two‐dimensional theory to be used to predict bulk sidearm properties such as total heat loss rate and return flow temperature.