Project Focus
Gravity currents formed by submerged outfall discharges in inland and coastal waters

Background and Motivation
Various municipal, agricultural, industrial, and domestic liquid discharges (e.g., waste water, heated water from power plants, brine slurry from desalination plants, dredged mud slurry) are routinely released, both intentionally and accidentally, into lakes, estuaries, reservoirs, and rivers. In many of these operations, the discharges occur through a submerged round outfall into the receiving waters. Understanding the interactions of the discharges into receiving or ‘ambient waters’ is of paramount importance for assessing and minimizing the adverse impacts associated with these discharges. The interaction of these discharged and the ambient fluids, occurring first as buoyant jets and then as gravity currents, begins immediately after the outfall release. The term ‘buoyant jet’ refers to the flow of a fluid driven by its momentum and buoyancy into another fluid, while ‘gravity current’ is the predominantly horizontal propagation of a fluid driven solely by its buoyancy into another fluid. This ongoing project focuses on the dynamics of gravity currents occurring in both inland and coastal waters formed by buoyant jet discharges caused by outfall discharges.

Fig. 1. gravity currents generated from the impingement of the buoyant jets on a boundary. (a). the vertically downward discharge of the denser (than ambient water) fluids, (b) the vertically upward discharge of lighter fluids, and (c) the angled upward discharge of denser fluids

Fig. 3. The anatomy of a two-dimensional gravity current  Notation: S-particle erosion from the bottom, D- particle deposition from the gravity current, α- angle of the bottom slope, Uf - velocity of the front, w e -entrainment velocity into the current, ρc- density of the current, and ρw -density of the ambient water.

Key Contributions
In the first part of the project, a comprehensive review of the dynamics of the different forms of gravity currents  formed by buoyant jet discharges from submerged single-port round outfalls in  inland and coastal waters has been completed. The review, appeared in Environmental Fluid Mechanics journal, provided the current state of the science of the dynamics of gravity currents generated by positively and negatively buoyant jet discharges from sub-merged round outfalls, especially on the followings:

• manmade discharge operations that generate bottom and free-surface gravity currents (Fig. 1).
• near-field dispersion regimes of the discharges before they change to gravity currents.
• analysis of the flow regimes characteristics of bottom and free-surface gravity currents in relatively calm ambient waters (Fig. 2) 
• analysis of the influence of the hydrodynamic forces (e.g., currents, turbulence, waves) on the dynamics of gravity currents
• quantitative models commonly used in modeling different forms of gravity currents generated from buoyant jet discharges. 
• current knowledge gaps and research needs.
  

Future research will investigate the advective effects of ambient current and waves, and the mixing caused by the ambient water turbulence on different forms of gravity currents.