Automation of the Rational Formula using GIS infrastructure – Case study Siret River Basin - Romania

Abstract

One of the main concerns and challenges of applied hydrology is estimating the peak flood discharge for an ungauged river. The method currently used in case of rivers with small catchment areas (less than 5 km²) is the Rational Formula as it had been proposed by Diaconu (1994) using the updated values of runoff coefficients presented by Miță (2019). Taking full advantage of the tools offered by the GIS software for digitizing the spatial information of the parameters related to a river and its catchment, this paper, for the first time in literature, approaches the Rational method as it is presented by Diaconu and Miță (1997), by means of an automated method based on GIS infrastructure, which greatly increases the accuracy of the results while significantly reducing the time needed to determine the end result. Therefore, using ArcMap software, one can create the necessary raster images based on DTM (30 m resolution), CLC 2018 shapefile and soil shapefile, an automated geoprocessing workflow with the help of Model Builder for extracting the necessary parameters for the Rational Formula, which will then be integrated in a custom Excel workbook that will generate the magnitude and frequency of peak discharge at the point of interest using a log-Pearson Type III probability distribution. This method has been applied on the Romanian catchment area of Siret river, but it can be used on almost all small river basins in Romania, because the given parameters and coefficients have been determined for the entire territory.

Keywords

• rational formula
• maximum discharge
• automation
• runoff coefficient