Jorg Imberger - Environmental Fluid Dynamics: Flow Processes, Scaling, Equations of Motion, and Solutions to Environmental Flows

Nature uses the properties of water and air to deliver nutrients and dispose of all its waste products. Natures strategy is based on three underlying principles. First, water and air move, so waste is removed from the immediate vicinity of the disposal site and so is out of sight, out of mind. Second, as the fluid moves the waste, turbulence disperses the concentrated waste quickly and effectively and dilutes the waste, to a small fraction of the original concentration, rendering it accessible for biological recycling. Third, once diluted the waste is transformed to food for other organisms by microbes, billions of workers transforming waste from one organism to food for another. This is the basis of all evolution, organisms filling niches where others have created a habitat with appropriate temperature, chemical composition, food and protection from predators.

Human traditional engineering designs adopted this strategy most effectively, but never closed the loop. Designs were and still are, based on the misconception that the aquatic and atmospheric domains are infinite and that caretaker microbes would always be available to take render harmless the waste being emitted into the domains. As we now know this is no longer the case, our chimneys, our sewage outfalls, our chemical disposal sites, both solid and liquid and most recently the increasing number of large-scale accidental spills are no longer being dispersed to low enough concentrations to be transformed to food in small contained domains; the initial concentrations are increasingly effecting very large areas and are, as a consequence, killing a huge number of living plants and animals, depleting our biodiversity at an alarming rate. Even more importantly, this depletion is breaking the very engine that sustains the transformation from waste to food and so the whole strategy is beginning to show signs of leading to a major ecological break down.

The transport and mixing that a fluid habitat services the biogeochemical world with are thus more important than ever. Historically, effluent removal by fluid transport was the key, assuming that somehow nature would do the rest. Then in the 1960s, it was observed that our wastes were too toxic and had to be diluted in the near field. Thus, an emphasis was placed on diffuser designs, engineering structures that would quickly and effectively dilute the waste with local ambient fluid. In the last 10 years, engineers have started to think in terms of assimilative capacity were the biota can effectively carry out the transformation from waste to food, before being impacted on by a neighboring effluent. However, at present this is only a vague concept, with the pressures of development usually outweighing the domain constraints of assimilative capacity.

This book is an attempt to provide some of the tools for waste cycling, rather than disposal, where all three factors are given equal importance. First, removal of the waste to a domain size where sufficient dilution may take place to allow for the biological transforms, second ensure appropriate dispersal to levels conducive for the microbial world and third, to provide a far field fluid environment that has mixing properties, from large domain scales to microbial rates of strain scales that foster biota that perform the transformations of waste to food.

Clearly, this is an enormous task, so I have focused on providing the basic overview, sufficient for the general environmental engineer and scientist, to a level that will allow the specialist to then turn to advanced texts in the particular special area of interest.

On and off I have taught this material over the last 40 years, at Berkeley, Caltech, Karlsruhe, Padova and Western Australia. are designed to provide the foundation for a serious student in Physical Limnology, Estuarine Dynamics or Coastal Oceanography. A student having completed a one-semester course using these two chapters should be able to move onto specialist text in Limnology, Oceanography and even Meteorology.