Temporal and spatial scales of lake processes. Part 1: physical and ecological scales, non-dimensional parameters and flow regimes

Scaling concepts, related to basic physical transport and mixing processes and other ecological
aspects in lakes, are reviewed in an ecohydrodynamic perspective; the length and time scales as
well as the non-dimensional parameters governing the various flow regimes and relevant to these
processes are also presented, emphasizing the influence they have on lake ecosystems. The
hierarchy of length scales is very important in determining both the turbulence structure, and in
affecting the ecological processes occurring in lakes. Most of these scales are defined in terms of
several basic parameters which, when combined properly, yield important dimensionless numbers,
as: Rf, Ri, Pr, T, Ret, Frt, Grt, and Prt, the flux and gradient Richardson numbers, the Prandtl
number, a dimensionless time, and the turbulent Reynolds, Froude, Grasshof and Prandtl numbers,
respectively. A few more dimensionless numbers (as the Lake and Wedderburn numbers, LΝ, W,
etc.) are also useful in characterizing the general dynamic behavior of lakes. Ratios of length or time
scales may also provide similar useful parameters.