Regionalization of flow duration curves in flow regimes of intermittent streams

M. Rianna, Regionalization of flow duration curves in flow regimes of intermittent streams, PhD thesis, 130 pages, Università di Roma "La Sapienza", December 2010.



Low flow analysis is a very important and widely studied topic in hydrology and water resource design and management. The knowledge of low flows periods and of the amount of available water is in fact fundamental in a wide range of scenarios. Conventionally low flow analysis is used for the design and operation of public water supply schemes, but another frequent application is the evaluation of dilution of waste water that arrives from industrial or domestic source into a river. The number of summary information derivable from daily time series that describes low flow regimes of a river is quite large. The big amount of methods is based mainly on the types of available data and the required output. One of the largely used tools to evaluate low flow and the river regime is the flow duration curve (FDC). This is a cumulative frequency curve that shows the percentage of time that a given discharge is equal or exceeded during a fixed period. The choice of this tool was done because it is one of the most informative methods of displaying the flow characteristics of a stream throughout the range of discharge, without regard to the sequence of occurrence. These curves are derived in gauged river data, but are essential also in rivers where the systems for collecting and managing water information are inadequate. The aim of this work is then to assess the reliability of existing regionalisation models of flow duration curves, to create a new model to calculate flow duration curves in rivers characterized by an intermittent regime and to apply a procedure of regionalisation starting from definition of homogeneous regions in the target area till arriving to the transfer of the hydrological information in ungauged basins. In particular the work shows a new method for calculating flow duration curves and annual flow duration curves in intermittent basins. This method joins the stochastic index theory (Castellarin 2004) that model the relationship between flow duration curves and annual flow duration curves of daily discharges to the Bayes’s theorem that can be used to determine the probability of occurrence of a non-zero event, given that a zero event is already occurred.

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