Full hydrogeological characterization of a sediment body must include a detailed description of its three-dimensional internal geometry. Where either direct methods or remote sensing are inadequate, computer simulations can be used to approximate the internal structure. A computer code, BCS-3D, was developed that simulates the three-dimensional internal geometry of sediment units for braided-stream deposits. Code development was based on the assumption that (1) a certain part of the surface (geomorphological) system is captured and preserved in the sedimentological record, and (2) characteristics of sediment units are a function of the localized flow energy as expressed by the Froude number. BCS-3D uses a random-walk approach to describe the formation of braided-channel networks. The concept of hydraulic geometry is incorporated to translate a two-dimensional topological network to a three-dimensional topographic surface. A series of these surfaces is stacked vertically with some offset, to produce a three-dimensional description of the internal architecture. Individual elements in the architecture are associated with specific sediment units based on a description of flow energy in the form of the Froude number. No comprehensive data set is available to validate this approach fully. However, the model was compared with and adequately matched a composite set of measurements from two studies in systems with similar physical characteristics, the Ohau River in New Zealand and the Squamish River in British Columbia, Canada.