Abstract

Stream net ratios for a sample of third- and fourth-order West Malaysian drainage basins are determined by stereoscopic methods. Bifurcation ratio is shown to take values similar to those published for a wide range of natural environments. Departures from the laws of drainage composition as defined by Horton and Schumm are studied by means of the within-basin ratio values. The standard deviation of the within-basin ratio values is taken as an index of the magnitude of departure, while the relationship of the within-basin ratios to order gives an indication of the type of departure.

Two physical causes, stream rejuvenation and approach to cyclic old age, are advanced to explain some of the observed ratio variability. Stream rejuvenation causes systematic changes in bifurcation ratio as related to order. Within-basin standard deviations for cumulative length, area, and cumulative slope ratios increase significantly when basin relief is reduced below about 200 feet. The increasing influence of base level as basin relief approaches zero thus causes departures from the laws of stream length, slope, and basin area.

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