Internal hydraulics of surface buoyant jets with high aspect ratio

Surface buoyant jets are commonly found in natural and engineered environments. Typical examples are rivers entering into the ocean, and wastewater discharges into water courses. The surface buoyant jet structure depends on the source properties, geometry and mixing processes. Predicting the mixing and spreading is the key challenge. Recent studies based on layered models have investigated the entrainment rate and spreading rate. However, frictional effects are also important in determining the thickness of the buoyant jet and its lateral spreading.  We will address the effects of entrainment, spreading and friction.

We investigate the surface buoyant jet over a sloping bottom through internal hydraulic theory and field measurements of a river flow into the ocean. In the nearshore zone, the river flow is attached on sea bottom due to the Coanda effect. With a decrease of momentum and thickening, the buoyant jet starts to lift off. At the detachment point, the buoyant jet is critical and the isopycnals are perpendicular to the bottom. We focus on large aspect ratios (river width to the depth) and predict layer thickness, entrainment, lateral spreading and interfacial friction. Comparisons are made with field measurements in Koombana Bay, Western Australia.