We discuss the coarsening of domains in bicontinuous structure of aqueous polymer mixtures, driven by hydrodynamic flow. Taking into account the bending energy as a contribution to the interfacial energy, we derive a general expression for the coarsening rate in these mixtures. Examining the limiting behavior of small and large length scales, we find two regimes. For small length scales, the size of the domains (Lambda) scales with time (t) as Lambda similar to T-1/3, while at large length scales, the domain size scales with time as Lambda similar to r. The crossover between the two regimes occurs at a particular length scale, the critical radius R-e, which is dependent on the bending rigidity k, and the interfacial tension of a flat interface gamma(0) (R-e =root 2-k/gamma(0)). In the case of aqueous biopolymer mixtures, we predict this particular length scale to be in the micron range. This new general expression for the coarsening of domains in aqueous polymer mixtures can explain experimental results [Loren et al. Macromolecules 2001, 34, 8117], which show the two regimes of coarsening with a crossover at 4 mu m.