Three-dimensional numerical model for flow through natural rivers

This paper presents a three-dimensional numerical model for simulating flow through natural river reaches. The model solves the Reynolds-averaged Navier-Stokes (RANS) equations closed with the standard k-ε turbulence model. Large-scale roughness and multiple islands are directly resolved by employing boundary-fitted curvilinear coordinates in conjunction with a multiblock approach. Small-scale bed roughness is accounted for using a two-point wall-functions approach. Calculations are carried out for flow through a 4-km stretch of the Columbia River, downstream of the Wanapum Dam, for which detailed field and laboratory measurements were collected for a range of power plant operating conditions. Measurements at one operating discharge are employed to calibrate the small-scale roughness distribution in the numerical model. Subsequently, the calibrated model is validated by comparing the computed results with laboratory and field measurements for other discharge combinations. These comparisons demonstrate the ability of the model to capture most experimental trends with remarkable accuracy.