Flow resistance of large-scale roughness in mountain rivers of the Western Cape

[摘要] ENGLISH ABSTRACT: This investigation arose out of the pressing need for alternatives to ineffective existingmethodologies for low flow measurement in boulder bed rivers, with particular focuson the mountain streams in the Western Cape.Both empirical and mathematical verification were regarded as important if progresswas to be made towards identifying a suitable approach. Historically the inability todetermine the frictional effect of the streambed on the flow rate has been a majorobstacle limiting the accuracy of flow calculations. From literature, the most likelyrelationship appears to be a power function, utilising hydraulic variables derived fromphysical parameters characteristic of a section of stream.Local Western Cape data was thus collected from various typical mountain streams,so that relevant analysis could be done. Testing of existing equations from literaturesources on this set of data revealed limited applicability.Subsequent empirical experimentation has shown that particle size is a dominantvariable in determining boulder bed flow resistance under low flow conditions.A mathematical approach was sought to provide a more suitable base for a locallyapplicable formula. Sediment transport theory, based on simple power conservationlaws, was successfully implemented, partially bridging the gap between theapplications for sand bed and boulder bed flow conditions respectively.After a certain degree of empirical adjustment, an equation form was finalised that isbelieved to be the most suitable for Western Cape mountain streams, with definitepotential for wider application, provided further research is done.

[发布机构] Stellenbosch University