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2 2015

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Influence of time of concentration on variation of runoff from a small urbanized watershed

Amatya D. M., Cupak A., Wałęga A.

Geomatics, Landmanagement and Landscape

2015

no. 2

7--19

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, małopolskie 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.

Usefulness of the Modified NRCS-CN Method for the Assessment of Direct Runoff in a Mountain Catchment

Wałęga A., Rutkowska A.

Acta Geophysica

2015

Vol. 63, no. 5

1423--1446

The aim of this study was to evaluate the usefulness of modified methods, developed on the basis of NRCS-CN method, in determining the size of an effective rainfall (direct runoff). The analyses were performed for the mountain catchment of the Kamienica river, right-hand tributary of the Dunajec. The amount of direct runoff was calculated using the following methods: (1) Original NRCS-CN model, (2) Mishra- Singh model (MS model), (3) Sahu-Mishra-Eldho model (SME model), (4) Sahu 1-p model, (5) Sahu 3-p model, and (6) Q_base model. The study results indicated that the amount of direct runoff, determined on the basis of the original NRCS-CN method, may differ significantly from the actually observed values. The best results were achieved when the direct runoff was determined using the SME and Sahu 3-p model.