How much hydropeaking? Development of a first screening approach to assess the level of hydropeaking pressures

The general aim of this work is to develop and test a preliminaryscreening approach to assess the level of hydropeaking pressure on a river reach, without explicitly focusing on its impacts. A combination of two indicators is proposed, in order to provide an easy-to-use methodology which can be applied on commonly available stream-flow data in alpine regions. The two indicators, HP1 and HP2, quantify the daily maximum intensity and the velocity of discharge variations, respectively. We analyzed data from two different Alpine areas: 28 flow gauging stations located in the Trentino area (NE Italy, 16 subject to hydropeaking and 12 not impacted reaches) and 37 flow gauging stations located in Switzerland (20 impacted and 17 not impacted reaches).The approach is based on the analysis of statistical properties of time series that can be built with two quantities related with the indicators. In the end every reach is represented by an unique value of HP1 and HP2, which reveals a statistically significant difference between impacted and non-impacted reaches, the latter considered as reference group. In particular, higher values of HP1and HP2 are associated with reaches which experience hydropeaking releases.In the space of the indicators we provide a quantitative definition of the “hydropeaking pressure” as a relative distance from not impacted conditions, based on limits for HP1 and HP2 calculated on not impacted group. Overall the proposed approach can easily inform on (i) relative distance of impacted reaches from not impacted conditions, (ii) provide thresholds to identify hydropeaking impacted reaches