Mauro Carolli

A simple procedure for the assessment of hydropeaking flow alterations applied to several European streams

Release of water from storage hydropower plants generates rapid flow and stage fluctuations (hydropeaking) in the receiving water bodies at a variety of sub-daily time-scales. In this paper we present an approach to quantify such variations, which is easy to apply, requires stream flow data at a readily available resolution, and allows for the comparison of hydropeaking flow alteration amongst several gauged stations. Hydropeaking flow alteration is quantified by adopting a rigorous statistical approach and using two indicators related to flow magnitude and rate of change. We utilised a comprehensive stream-flow dataset of 105 gauging stations from Italy, Switzerland and Norway to develop our method. Firstly, we used a GIS approach to objectively assign the stations to one of two groups: gauges with an upstream water release from hydropower plants (peaked group) and without upstream releases (unpeaked group). Secondly, we used the datasets of the unpeaked group to calculate one threshold for each of the two indicators. Thresholds defined three different classes: absent or low pressure, medium, and high pressure, and all stations were classified according to these pressure levels. Thirdly, we showed that the thresholds can change, depending on the country dataset, the year chosen for the analysis, the number of gauging stations, and the temporal resolution of the dataset, but the outcome of the classification remains the same. Hence, the classification method we propose can be considered very robust since it is almost insensitive to the hydropeaking thresholds variability. Therefore, the method is broadly applicable to procedures for the evaluation of flow regime alterations and classification of river hydromorphological quality, and may help to guide river restoration actions.

A graphical approach to characterize sub-daily flow regimes and evaluate its alterations due to hydropeaking

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.

Habitat Indices for Rivers: Quantifying the Impact of Hydro-Morphological Alterations on the Fish Community

Habitat simulation models are effective tools which can be used to estimate spatial and temporal habitat availability for aquatic organisms, and to design and evaluate habitat restoration actions. Based on the meso-scale resolution, the present work proposes two indices to evaluate the spatial and temporal alteration of instream habitats. Firstly, the Index of Habitat Quantity (IHQ) describes the relative amount of habitat loss due to flow diversion, and, secondly, the Index of Habitat Stress Days (IHSD) measures the increase of continuous duration of events when habitat bottlenecks create stress to the fauna. Two case studies from the mountainous areas of Northern Italy are presented as applicatory examples. The achieved results indicate that (i) the meso-scale can be considered an appropriate scale resolution to link fish habitat requirements to fluvial morphological characteristics, and (ii) the proposed indices are flexible tools since they can capture both spatial and temporal alterations of habitat structure and can be applied to different kind of pressures (e.g., hydropower generation, hydropeaking).