Influence of time of concentration on variation of runoff from a small urbanized watershed
The main objective of the paper is to estimate the influence of time of concentration (TC) on maximum flow in an urbanized watershed. The calculations of maximum flow have been carried out using the Rational method, Technical Release 55 (TR55) procedure based on NRCS (National Resources Conservation Services) guidelines, and NRCS-UH rainfall-runoff model. Similarly, three methods were used to calculate the overland flow component of the TC: the Kerby method, the Morgali and Linsley method and the NRCS travel time method. The TC was calculated in a watershed located in Krakow city in Poland, malopolskie voivodeship. Total area of the watershed has about 180 ha. It’s a highly urbanized watershed with a significant land cover (29.6% of total area) influencing the runoff, in the form of an impervious industrial area. The highest value of time of concentration was achieved for Morgali and Lindley method in case of the subwatershed with dominant pervious areas, as opposed to the NRCS method for the subwatershed with dominant impervious areas. The highest value of TC was obtained for NRCS method. With reference to the whole watershed, the highest values of the time of concentration were obtained for the MorgaliandLindley method and the lowest for the Kerby formula. Based on this study, authors recomended the Kerby method for estimating TC for overland surface dominated areas because this method requires only a small number of input parameters, that are straightforward to estimate.