Influência de parâmetros fisiográficos no tempo de concentração de bacias hidrográficas do estado do Rio de Janeiro (RJ) e do município de Fortaleza (CE)

Abstract

Time of concentration (tc) is a relevant variable for estimating peak flows in hydrological and hydraulic projects. This parameter makes it possible to understand the behavior of the basin in relation to surface runoff, in addition to its importance for the management of water resources. From this perspective, the present study aims to estimate the concentration time (tc) in watersheds in the state of Rio de Janeiro and the municipality of Fortaleza, and to evaluate the sensitivity of tc in relation to the physiographic parameters of the study basins. For this, geospatial data and geoprocessing tools associated with Geographic Information Systems (GIS) were used to obtain physiographic parameters. The QGIS software was used to obtain this information for both study sites. Subsequently, the times of concentration were calculated by means of 10 empirical formulas based on morphometric characteristics of different watersheds. Subsequently, the influence of pelvic area, talweg length and slope on the tc result was evaluated. The results found for the basins of the state of Rio de Janeiro and the municipality of Fortaleza revealed high variability in the concentration times for the same basin. The tc had a minimum of 0.306 h and a maximum of 52 h for the Fortaleza basins. For Rio de Janeiro, minimum and maximum values of 1.306 h and 443.69 h were obtained, respectively. The Passini equation resulted in overestimated values of time of concentration for the three physiographic parameters analyzed and in both sites investigated. On the other hand, the Dooge equation, in relation to the other equations, presented shorter times in relation to the other methods evaluated. When examining the slope of the talweg in the basins of Fortaleza, there was greater variability of the tc for larger slopes, while for those of the State of Rio de Janeiro, there was a small variation for the methods of Dooge and Ventura, in smaller slopes. By analyzing the physiographic parameters individually, it was found that the other variables considered by the experimental equations also interfere in the calculation of the time of concentration, as well as its sensitivity in relation to the slope, with the influence of the area and/or length of the thalweg in some equations. It should be noted that the sensitivity of empirical equations is related to their previous conditions of elaboration, such as the place where they were designed, a fact that affects the results achieved. Finally, studies on the time of concentration allow a better understanding of the behavior of water in watersheds, being, therefore, an important reference variable for the prevention of extreme events associated with human intervention and climate change, such as floods and floods, in addition to its application in the design of hydraulic works.