El perímetro de una cuenca hídrica: su tratamiento objetivo en la definición de índices geomorfológicos

Abstract

Dimensionless shape indexes are usually used to relate the form of a watershed with their hydrological response. These indexes relate the area A and the “smoothed” perimeter of a watershed, like Gravelius compactness coefficient. The perimeter depends on the spatial resolution on which is determined. In order to turn objective the shape index, we propose to replace the watershed border by a polygonal of “basic segments” Sb equals and consecutive, so the perimeter is delimited once the segment have been chosen. Furthermore, we propose to relate Sb to , making these indexes invariant with respect to A and turning possible to make objective comparisons. The length of Sb was varied from a quarter to twentieth of , in three different basins. At these levels of length, the polygonal remove certain details but preserve the shape of the watershed. It has been proof a good fit in a lineal log-log relationship between the basic segment and the quantity of segments in the perimeter, proving that the watershed border behave like a fractal object. Furthermore, the variation of the Gravelius coefficient in function of the length of the basic segment was analyzed. We propose to use Sb=1/5 for shape indexes, and Sb=1/20 for indexes relating river lengths.