(3) EXPERIMENTAL STUDY OF CONNECTIVITY IN MEANDERING RIVERS: IMPLICATIONS FOR STRATIGRAPHIC STRUCTURE OF BURIED CHANNELS
Matthew Czapiga, Gary Parker
University of Illinois Urbana-Champaign Urbana, Illinois 61801 USA
Meandering rivers define pathways for water flow, sediment movement, nutrient transport, fish passage and navigation. Buried subaerial and submarine meandering channels often define ribbons of sand which create connected reservoirs for hydrocarbons. Yet the degree to which meandering channels are connected is a relatively understudied problem. In general, we can pose the connectivity problem as follows. What is the probability that a continuous path of length L and width B exists such that some attribute A falls within specified bounds throughout the path? One example of this is navigation: what is the probability that a ship requiring a minimum depth Hmin can navigate a continuous path without going aground? In the case of stratigraphy, the question can be posed in terms of a continuous pathway of length L over which hydraulic conductivity never falls below a specified limit. The longer the connected path, the more efficiently hydrocarbons could be extracted from a single well. Here we report on experiments in a highly sinuous channel with an erodible bed. We study connectivity in terms of the probability P(L, B, Hmin) that starting from a given point, a downstream path with length L and width B is connected in the sense that H never falls below Hmin. We develop dimensionless functional relations for P in terms of bankfull geometric parameters, and also study how changing river stage affects connectivity. Our work underlines the profound effect that dynamic changes in river bed planform can play on connectivity.