A Reduced Rank Model of Drainage Basin Morphology

Abstract

The existence of groups of highly intercorrelated variables among the large number of parameters widely used for quantifying drainage basin morphology suggests the possibility of reducing them to fewer dimensions. Through principal axis factor analysis of 37 morphometric properties of 52 third-order basins in the Udi-Awgu cuesta of south-eastern Nigeria, six factors identified as measures of intensity of dissection, stream network size, relief, shape, link length ratio and bifurcation ratio, are found to account for 92 per cent of the variance in the data. The factor-defining variables are total drainage density, total stream length, relief ratio, lemniscate ratio, link length ratio and bifurcation ratio respectively.

These findings are essentially similar to those obtained for the third-order basins of southern Uganda, western U.S.A., southern Indiana, Barbados and Tobago. These studies suggest that, irrespective of differences in climate, lithology and vegetation cover, the morphology of drainage basins may be adequately quantified by measurement and analysis of these six variables which thus constitute the parameters of the reduced rank model of the morphology of drainage basins. Explanations are offered for the orthogonality of these dimensions, and their geomorphic and hydrologic importance are briefly reviewed.

The identification of these underlying dimensions will not only simplify future morphometric work but also provide criteria for an objective multi-dimensional morphological classification of drainage basins.