Abstract

Geomorphic indices are extremely useful for the study of drainage basins. Nonetheless, it is not always possible to carry out a complete and integrated analysis of all the available indices because of their different way of representation. A case study of the Conca river basin in central Italy it is describes here, where the need to understand the relationships between the intensity of erosive processes and basin asymmetry made it necessary to analyse and to compare two geomorphic indices: the asymmetry factor (AF) and the energy of relief (Er). This basin has the characteristic of displaying strong left asymmetries in the upper and lower part that, for some authors, are caused by the different intensity of erosional processes on the opposite sides of the basin due to the their orientation. To study in great detail the asymmetry factor (AF) and the relief energy (Er) and their relationship along the entire basin a new method of calculating and representing these two geomorphic indices was created. Using this method these parameters were comparable and provided useful information to explain whether a correlation between asymmetry and erosion due to the orientation exists, that would otherwise be difficult to obtain with traditional methods. The data obtained highlight that in the upper and lower part of the Conca basin there is not any direct relationship between the asymmetries and the intensity of erosive processes on the sides of the basin. The results of this analysis, supported by other investigations such as satellite imagery observations and field evidences, show that the asymmetries seem to be due to different causes instead to orientation which may have had a marginal role only. This study also showed that, by applying methods of calculation and representation of the complementary geomorphic indices AF and Er, it is possible to increase the quantity and the quality of data. This can widen the scope and applications of geomorphologic and geomorphometric studies, and particularly applies to AF. The use of the AF index has previously been limited in drainage basins where the asymmetry alters; however, if the methods described in the present study are used, the parameter AF can successfully be applied to all types of drainage basins.

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