Calculation of bed changes in mountain streams

Simulation of flow and sediment transport in mountain streams is complicate d by the presence of high gradients, abrupt changes in geometry, variations in regime of flow, and large roughness elements. Most of the numerical mod els to predict aggradation and degradation in alluvial channels have been d eveloped for low-gradient rivers. This paper is devoted to the development of a numerical model to calculate bed elevation and grain size distribution changes in mountain streams where the maximum bed material size is in the range of boulders. An attempt is made to validate the model by using observ ed field data collected upstream from a small retention dam in a Venezuelan stream. After calibration of the sediment transport equation, reasonable a greement is obtained for the variations in the grain size distribution of t he bed-surface material. An additional application is presented in the Coco rotico River, a small mountain stream located in the northwest region of Ve nezuela, which illustrates the adaptability of the model to handle a case o f coarsest-bed-material removal from the active channel and to simulate the armoring process.