Author(s): Elena Carcano; Paolo Bartolini
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Keywords: Peak-maximum daily streamflows; R ratio
Abstract: Torrential catchments are characterized by great discharges between streamflow peaks and their corresponding mean daily values. Conversely, the same cannot be said in case of ordinary flows or, even, draughts. In such cases, in fact, the difference between the instantaneous flow and its corresponding daily datum (generally observed at 9 a. m. according to an Italian custom) becomes irrelevant especially for those watercourses of torrential and intermittent regime. For such basins, in fact, low runoffs easily tend to almost zero value and the difference between the two flows of reference is totally inappreciable. Daily flows, available for small number of catchments in a region and mostly limited at specific sites, have been published in a systematic way till the end of 1970s by Servizio Idrografico dello Stato (see Annali Idrologici) and are, recently (2000s) in charge by Arpa Institutions. On the contrary, information on flow peaks (which represent the basis to assessing streamflow design values at assigned return periods useful for land planning and management) are difficult to be found. In this work two torrential catchments belonging to an hydrologically homogenous region, in Italy, are investigated. The adopted procedure introduces several flow thresholds and counts the number of floods which overtake the value of reference; the return period T is later on evaluated. A comparison between streamflow peaks and corresponding daily data is carried out, thus evaluating the corresponding ratio R. R enables to assess peak values for those flood events during which information lacks because of level sensor malfunctioning or, in the most practical circumstance, because only daily flows are available. The reconstruction of an historical sequence of peaks, allows a more concrete estimation of design streamflow values and provides knowledge on floods intensity.
Year: 2014