Power production by hydro-electric facilities according to rapidly varying demand on the electricity market (hydropeaking) may lead to unnatural fluctuations in flow and stage in rivers downstream of power plant outlets.

We developed COSH-Tool, a computational tool for automated analysis of time series in order to quantify these rapid fluctuations with the purpose of assessing impacts on the river ecosystem. COSH-Tool is a user-friendly analysis tool with a simple interface requiring no coding from the user. COSH-Tool can calculate values for a set of parameters which describe (1) the magnitude of the variations, i.e. how intense the variations are, (2) the scale of time, i.e. how rapid and when the changes in flow and stage occur, (3) the frequency i.e. how often or regular they appear. The analysis consists of several steps starting from data processing to parameters calculation. Finally COSH-Tool provides a statistical description of parameters and a graphic illustration with box plots, histograms, and time series plots. The rapid fluctuations are identified by establishing river and data specific thresholds for the rate of change in flow and stage. Rapid increases and rapid decreases are analysed separately because they are related to different impacts such as drift of invertebrates or stranding of juvenile fish respectively. Recently we implemented seasonal analysis considering biologically significant periods of the year (e.g. fish spawning) and light condition analysis (daylight, twilight or darkness) at the time of peaks occurrence.

A demonstration of the analysis tool is presented for the Norwegian regulated river Mandalselva.