Script > Ch 5
5: Boundary mixing: Air-water and sediment-water
In the previous chapter we introduced
transformation and described both homogeneous and heterogeneous
reactions. Now, we would like to look in more detail at heterogeneous reactions and discuss the
chemical and physical processes at interfaces that lead to boundary
fluxes of chemical species. The two major boundary types in environmental
fluid mechanics are the air-water and sediment-water interfaces.
Because the processes at both boundaries are very similar, we treat them
together in this chapter under the heading of boundary exchange.
This chapter is divided into three main sections. First, the
boundary layer in the vicinity of the interface is described, and two common models for treating the
boundary dynamics are introduced without specifying what type of boundary is involved.
Second, the air-water interface is introduced, and methods are described for treating gas
exchange across the interface. As an example, the Streeter-Phelps equation for predicting oxygen concentrations
downstream of an organic waste stream is introduced. Third, the
sediment-water interface is described, including the complex physical and transformation processes that bring sediment and
water into contact, and a short description of the chemistry that occurs at the sediment-water interface is
See Lecture 9 and