Morphometric indices at different scales applied to the danger of flooding in small basins. Basin of the stream San Bernardo, Argentina

Abstract

Fluvial morphometry aid in the interpretation of morphodynamic and hydrological behavior in watersheds. The determination of the scale of work is important since a change in it generates a variation in the results and modifies the applicability of the indexes. But does this variation occur in all the indexes? The objective of this work is to study fluvial morphometry and compare morphometric indices at different spatial scales in the San Bernardo river basin. It is located in the center-south of the Sistema de Ventania, Buenos Aires (Argentina). It has an area of 82 km2, it does not have capacity and it generates torrential floods before the occurrence of intense precipitation events (100 mm / 24 h). The results obtained were compared at a scale of 1: 50.000 (official cartographic scale of greater detail in Argentina) and 1: 1.400 (scale closest to the reality of the basin obtained from Google Earth). The parameters of area (A), perimeter (P), channel length (lc), height (h), slope (D), slope and the indices were calculated: Ratio of elongation (Re), Reason of relief (Rr), Relief ratio (R), Bifurcation ratio (Rb), Length ratio (Rl), Torrentiality coefficient (Ct), Drainage density (Dd) and Drainage frequency (Fd) relevant to the study of floods. The results of the Rb and Re indixesassociated with the topology and shape respectively reveal a basin with high potential to generate torrential floods. The values obtained for the Dd and Ct indices reinforce what has been said previously. In both, scales the indexes maintain in the rank of classification, however, those of major scale approach the real situation. The use of more detail, as in this case, allows to improve the results in small basins and in indexes influenced by the properties of the drainage network.