Avaliação de métodos de tempo de concentração e sua influência no cálculo da vazão em microbacias urbanas

Abstract

Concentration time is an essential parameter in the estimation of peak flows in hydrological projects, widely used to obtain certain values in rainfall and hydrograph calculations. It represents the time required for the water to travel the entire length of the hydrographic basin, from the farthest point to the outlet. This parameter is influenced by factors such as slope, channel roughness, length of the thalweg, land use and occupation and percentage of impermeable area. Understanding the behavior of the basin in relation to concentration time is essential to prevent and mitigate the effects of natural disasters. Despite its impact, it is a challenge to determine its value and find the correct formula to apply, and there is a difficulty in obtaining reliable information about such methods. There are several formulas to calculate concentration time, each with its own particularities. The objective of this monograph is to compare different methods of calculating the concentration time in urban watersheds and to evaluate how these variations interfere with the calculated flows in a specific watershed. This work analyzed 10 formulas recommended by the Manual of Basic Hydrology for Drainage Structures of DNIT, by the Manual of Urban Drainage of Teresina and Master Plan of Urban Drainage of Teresina. These formulas were applied in an urban watershed of Teresina, PD14, taking into account its geographical and hydrological specificities. The method used to calculate the flow was used in order to estimate project flows by means of the HEC-HMS software, taking into account physiographic data of the basin, partially executed with data from INPE and IBGE and the aid of QGIS version 3.28.8. Observed a high rate of dispersion among the methods of calculating concentration time, which can lead to oversizing, undersizing or optimal sizing.