Horizontal transport induced by upwelling in a canyon-shaped reservoir

Abstract

Several processes associated with spatial variations in buoyancy flux and mixing set up local and lake-wide horizontal temperature gradients, that in turn drive slow gravitational currents. These motions can dominate the horizontal transport and re-distribution of biological and chemical material. Here intrusions, indicative of horizontal transport, are identified in field data from a small drinking water reservoir, and the origin and character of the flows investigated using a 3-dimensional (3D) hydrodynamic model. It is shown that a horizontal temperature gradient is set up along the surface layer, due to upwelling shifting the metalimnion closer to the surface towards the upwind region, leading to a spatial variation in entrainment. The flows driven by these gradients form significant mass flux paths, enhancing exchange with the boundaries and controlling the fate of upwelled fluid. Further, the interaction of these currents with other hydrodynamic conditions is explored; namely the interaction with surface wind-driven currents, and the influence of different internal seiches generated by alternative lake bathymetries.

The baroclinic response to wind in a multiarm multibasin reservoir

“…This advection of metalimnetic water masses caused a so-called metalimnetic intrusion (Appt et al 2004); a relatively rapid divergence of metalimnetic isotherms progressing along the thalweg as registered at mooring NA. Similar observations of adjustment of metalimnetic thickness after removal of wind forcing were made in laboratory flumes (Monismith 1986), the subbasin of Upper Lake Constance (Appt et al 2004), and the single-basin Mundaring Weir Reservoir (Okely and Imberger 2007). The metalimnetic intrusion in Knewstubb and Natalkuz Lakes was more similar to the intrusion in single-basin lakes and not associated with the reflection of an internal surge as observed by Appt et al (2004) in the subbasin of Upper Lake Constance.…”

Approximation of the hydrostatic Navier–Stokes system for density stratified flows by a multilayer model: Kinetic interpretation and numerical solution

“…Thermo-hydrodynamical phenomena in lakes subject to the action of wind have been studied since a long time, by means of observations and measurements in situ [35,36], laboratory experiments [36][37][38][39], theoretical analysis [40][41][42], and, more recently, numerical simulations [43,44,3,45].…”

Stochastic characterization of the onset of and recovery from hypoxia in Tokyo Bay, Japan: Derived distribution analysis based on “strong wind” events

“…Thus, in an enclosed bay, DO concentrations decrease with increasing stratification, with the result that hypoxia develops in the lower layer adjacent to the seafloor, leading to harmful impacts on both aquatic plants and animals. Under these circumstances, upwelling induced by wind stress can sometimes bring this hypoxic water to the surface, where it is then transported outward and onward due to horizontal circulations within the bay, causing the spread of hypoxic water at the surface over large areas, which is a major public health concern [ Stevens and Imberger , 1996; Okely and Imberger , 2007; Maruya et al , 2010]. Therefore, it is highly important that the mechanisms leading to the occurrence and transportation of hypoxic waters are clarified, the role of external forces such as wind stress and riverine freshwater discharges quantified, and the episodic occurrence of and recovery from hypoxic conditions predicted.…”