## Empirical Equations for Combined Wind and Bottom ShearInduced Turbulence

In inland water bodies the combined effects of bottom-shear- and wind-shear-induced turbulence are often important. This occurs, for example, in the transition flow from streams or rivers into lakes, reservoirs, or the sea. As the stream velocity decreases, the wind effects can become increasingly more important, if not dominant. Especially interesting in that context are estuarine flows in which the channel flow regime is also time variable due to tidal effects.

In order to determine which regime dominates in such transitions, the transfer velocities for bottom, KLb (e.g., given by any of the eqns [10]-[14]), or for wind shear, KLW (given by eqns [17] or [18]), can be used as indicators. If KLW ^ KLb then the gas transfer is controlled by wind-shear turbulence, whereas when KLb ^ KLw bottom-shear turbulence dominates. The transition is given by KLb~KLw. Using, for example, eqns [14] and [18], the transition equation is fu3\ 1/8

The interaction process under combined bottom-shear and wind-shear effects is clearly a nonlinear one and a simple additive model should not suffice. Nevertheless, Chu and Jirka found that a linear additive model,

well approximates existing data sets for these combined turbulence effects.

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