SIMULATING THE 3-DIMENSIONAL DISTRIBUTION OF SEDIMENT UNITS IN BRAIDED-STREAM DEPOSITS

Full hydrogeological characterization of a sediment body must include a detailed description of its three-dimensional internal geometry. Whe re either direct methods or remote sensing are inadequate, computer si mulations can be used to approximate the internal structure . A comput er code, BCS-3D, was developed that simulates the three-dimensional in ternal geometry of sediment units for braided-stream deposits. Code de velopment was based on the assumption that (1) a certain part of the s urface (geomorphological) system is captured and preserved in the sedi mentological record, and (2) characteristics of sediment units are a f unction of the localized flow energy as expressed by the Froude number . BCS-3D uses a random-walk approach to describe the formation of brai ded-channel networks. The concept of hydraulic geometry is incorporate d to translate a two-dimensional topological network to a three-dimens ional topographic surface. A series of these surfaces is stacked verti cally with some offset to produce a three-dimensional description of t he 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 com pared with and adequately matched a composite set of measurements from two studies in systems with similar physical characteristics, the Oha u River in New Zealand and the Squamish River in British Columbia, Can ada.