EVALUATION OF OPTIMAL CHANNEL NETWORK AND RIVER BASIN HETEROGENEITY CONCEPTS USING MEASURED FLOW AND CHANNEL PROPERTIES

The optimal channel network (OCN) concept provides a physical argument for the form of river networks based on testable hypotheses relating to the exponents of the downstream hydraulic geometry relationships an d the variation of longitudinal slope along the channel. Measurements made over 5-day periods of steady flow in two catchments of areas 121 and 158 km(2) are described. At each site in each basin measurements o f the flow, channel cross-section and elevation have been made. A tota l of 340 measurements were made in one basin and 308 in the other and provide one measurement for about every 0.5 km of channel. The data ar e used to test the OCN concept. Less extensive data from two larger ca tchments are also used to help with the evaluation. The results do not support the depth, velocity and slope exponent values derived in the OCN concept. Analysis of the cumulative distributions of the spatially distributed flows shows agreement at flows above 6 l s(-1) with resul ts derived for aggregation systems with constant injection of mass of which the OCN concept is a specific example. Reasons for the differenc es from the OCN-derived exponents are discussed in terms of the hetero geneity of basin properties. (C) 1997 Elsevier Science B.V.