title: A graphical approach to characterize sub-daily flow regimes and evaluate its alterations due to hydropeaking.
abstract: Most flow regime characterizations focus on long time scale flow patterns, which are not precise enough to capture key components of short-term flow fluctuations. Recent proposed methods describing sub-daily flow fluctuations are focused on limited components of the flow regime being unable to fully represent it, or on the identification of peaking events based on subjectively defined thresholds, being unsuitable for evaluations of short-term flow regime alterations through comparisons between regulated and free-flowing rivers. This study aims to launch an innovative approach based on the visual display of quantitative information to address the challenge of the short-term hydrologic characterization and evaluation of alteration resulting from hydropeaking. We propose a graphical method to represent a discrete set of ecologically relevant indices that characterize and evaluate the alteration of sub-daily flow regimes. The frequency of occurrence of classified values of a descriptive hydrological variable is represented in a map-like graph where longitude, latitude and altitude represent the Julian day, the value of the variable and the frequency of occurrence, respectively. Subsequently, we tested the method on several rivers, both free-flowing and subjected to hydropower production. The advantages of our approach compared to other analytical methods are: (i) it displays a great amount of information without oversimplification; (ii) it takes into account changes in the intensity, timing and frequency of the sub-daily flows, without needing a priori defined thresholds to identify hydropeaking events; and (iii) it supports the Water Framework Directive goal. Specifically, results from applications of our graphical method agree with Sauterleute and Charmasson (2014) analytical method.
authors.affiliation: Department of Natural Systems and Resources, Technical University of Madrid (UPM), Ciudad Universitaria, SN, 28040 Madrid, Spain. Electronic address: carlos.alonso@upm.es.
authors.forename: Carlos
authors.initials: C
authors.lastname: Alonso
authors.affiliation: Department of Natural Systems and Resources, Technical University of Madrid (UPM), Ciudad Universitaria, SN, 28040 Madrid, Spain. Electronic address: alfonso_roman100@hotmail.com.
authors.forename: Alfonso
authors.initials: A
authors.lastname: Román
authors.affiliation: Landscape Ecology Group, Department of Ecology and Environmental Science, Umeå University, SE-901 87 Umeå, Sweden. Electronic address: mariadolores.bejarano@upm.es.
authors.forename: Maria Dolores
authors.initials: MD
authors.lastname: Bejarano
authors.affiliation: Department of Natural Systems and Resources, Technical University of Madrid (UPM), Ciudad Universitaria, SN, 28040 Madrid, Spain. Electronic address: diego.gjalon@upm.es.
authors.forename: Diego
authors.initials: D
authors.lastname: Garcia de Jalon
authors.affiliation: Department of Civil, Environmental and Mechanical Engineering, University of Trento, Via Mesiano 77, Trento, Italy. Electronic address: mauro.carolli@unitn.it.
authors.forename: Mauro
authors.initials: M
authors.lastname: Carolli
keywords: Ecohydraulics; Flow regulation; Graphical characterization; Hydropeaking; Hydropower; Short-term flow fluctuation