Geographia Technica, Vol 9, Issue no. 1/2014, pp. 31-38

USING GIS TECHNIQUES FOR ASSESSING LAG TIME AND CONCENTRATION TIME IN SMALL RIVER BASINS. CASE STUDY: PECINEAGA RIVER BASIN, ROMANIA

Romulus COSTACHE

ABSTRACT: Pecineaga River, which is a tributary to Buz─âu River, forms a small river basin. Its low surface and its almost circular shape, but also high slopes exceeding 20% cause a high potential for flash-floods on slopes. Given the fact that Pecineaga river basin is not being hydrometrically recorded, various rain-flow models which use water lag time and concentration time as calibration parameters for modelling flash-flood hydrographs. In this study, lag time was firstly computed by the formula proposed by Soil Conservatin Service from USA. This formula contains, besides certain constants, values of parameters such as: L-hydraulic length catchment; CNaw - weighted average value of the Curve Number; and Y- average slope of the river basin. These values were obtained through a work flow in ArcGIS 10.1. Having obtained these values, time lag was calculated for the closure section of the river basin. The result of time lag was used in order to determine the concentration time (Tc). The low values of the two parameters demonstrate that Pecineaga river basin is exposed to flash-flood on slopes.


Keywords: lag time, concentration time, Pecineaga, Curve Number.

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