A GEOMORPHOLOGICAL APPROACH TO THE IDENTIFICATION AND CLASSIFICATION OF INSTREAM FLOW ENVIRONMENTS

Abstract

Summary This paper highlights the considerable confusion that exists within the ecological literature concerning the classification of the lotic (flowing water) environments. A large number of ill defined terms has been introduced by various authors; these often relate to better defined geomorphological features, but are used more loosely by ecologists. This paper highlights the lack of consistency that exists and a number of recommendations are made in an attempt to alleviate the general confusion. Before attempting to provide an objective technique for a more rigorous classification, the relationships between the abiotic environment in which a community of species exists (biotope) and the channel form features recognised by fluvial geomorphologists (morphological unit) are examined. A link between the two is made through the description of the hydraulics of river flow. The Froude and Reynolds numbers are two dimensionless values frequently referred to by hydraulic engineers, and are used in this paper to characterise flow within a single reach of the Great Fish River (Eastern Cape). Exploratory data analysis shows that the Reynolds Number of mean flow does not appear to be very useful for the objective definition of biotopes, whereas the converse is true for the Froude Number. The results indicate that the use of the Froude Number, and variations of the Reynolds Number (roughness Reynolds Number), need to be tested for a wider data set.