Multiblock numerical model for natural rivers

A three-dimensional numerical model for simulating turbulent flow through natural river reaches with islands is developed. Unlike most available numerical models - which typically employ depth-averaged approaches - the present method is capable of simulating the complex patterns of secondary flow which are responsible for three-dimensional transport and mixing. The model employs the three-dimensional, Reynolds-averaged Navier-Stokes equations along with the k-ε model for turbulence closure. The governing equations are formulated in generalized, non-orthogonal, curvilinear coordinates in order to facilitate the modeling of river reaches with complex topographic features. The presence of islands and/or rock outcrops is accounted for by employing a multi-block grid generation approach which facilitates the discretization of complex multi-connected domains. The capabilities of the proposed method are demonstrated by applying it to calculate turbulent flow through a simplified river geometry - a 90 degree rectangular bend with a model `island' near its inner wall. Preliminary calculations for a natural river channel - a two-mile reach of the Colombia River, downstream of Wanapum dam - are also presented and discussed.