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The computational tool InSTHAn (indicators of short-term hydrological alteration) was developed to summarize data on subdaily stream flows or water levels into manageable, comprehensive and ecologically meaningful metrics, and to qualify and quantify their deviation from unaltered states. The pronunciation of the acronym refers to the recording interval of input data (i.e., instant). We compared InSTHAn with the tool COSH-Tool in a characterization of the subdaily flow variability of the Colorado River downstream from the Glen Canyon dam, and in an evaluation of the effects of the dam on this variability. Both tools captured the hydropeaking caused by a dam operation, but only InSTHAn quantified the alteration of key flow attributes, highlighting significant increases in the range of within-day flow variations and in their rates of change. This information is vital to evaluate the potential ecological consequences of the hydrological alteration, and whether they may be irreversible, making InSTHAn a key tool for river flow management.

Flow regulation affects bordering riparian plant communities worldwide, but how different plant life forms are affected by river regulation still needs further research. In northern Sweden, we selected 10 rivers ranging from free-flowing to low, moderately, and highly regulated ones. In 94 reaches across those rivers, we evaluated the relative abundance of woody and herbaceous (i.e., graminoids and forbs) life forms, their species richness, and their relative presence. We also explored which, and to what extent, hydrological variables drove species assembly within each life form. The relative abundance and species richness of each life form decreased across river categories with increasing levels of regulation. This was particularly apparent in herbaceous life forms, and the most drastic decreases were observed in all life forms in moderately or highly regulated reaches. Additionally, when river regulation increased, the relative presence of many species from all life forms decreased. Unlike woody species, only a few new herbaceous species appeared in regulated reaches. A canonical correspondence analyses (CCA) revealed that a wide range of hydrological variables explained the occurrence of woody species, while fewer variables explained variation in the graminoid and forb life forms. We conclude that flow regulation and its intensity result into clear shifts in the relative abundance of different life forms, as well as in changes of within-group species richness and composition. Consequently, the modification of certain flow attributes in flow regulation schemes, as well as the intensity of these modifications, may alter the ratio between herbaceous and woody species, ultimately impacting the functions and benefits derived from each life form., Special Issue: Spatial and Temporal Patterns and Ecosystem Services of Riparian Forests

Hydropeaking, defined as frequent and rapid variation in flow in regulated rivers with hydropower plants over a short period of time, usually sub-daily to weekly, alters hydraulic parameters such as water levels or flow velocity and exerts strong impacts on fluvial ecosystems. We evaluated the effects of hydropeaking on riverbank vegetation, specifically assessing the germination and establishment of seedlings and cuttings of plant species representing a variation in traits. We used seeds and seedlings and cuttings varying in size as phytometers, and transplanted them to riverbanks both above and below dams used for hydropower production in northern Sweden, selected to represent a gradient in hydropeaking intensity, and along a free-flowing reach. We also analyzed sub-daily water-level variables modified by hydropeaking to identify variables key in explaining the observed vegetation patterns. We found that plant responses to hydropeaking varied with species, with flood-intolerant species being the most strongly affected, as early as the germination stage. In contrast, seeds of flood-tolerant species managed to germinate and survive the early establishment phase, although strong erosive processes triggered by hydropeaking eventually caused most of them to fail. The fate of flood-intolerant species identifies germination as the most critical life-history stage. The depth and frequency of the inundation were the leading variables explaining plant responses, while the duration of shallow inundation explained little of the variation. The rise and fall rates of water levels were key in explaining variation in germination success. Based on the results, we propose restoration measures to enhance establishment of riparian plant communities while minimizing the impact on hydropower electricity production. Given the strong decrease in the germination of species intolerant to prolonged flooding with hydropeaking, planting of seedlings, preferably of large sizes, together with r

[EN] This study proposes a stochastic methodology for the allocation of seasonal dam maximum conservation levels optimizing regular operation and hydrological dam safety. Furthermore, this methodology accounts the influence of accounting initial reservoir level variability. The methodology was applied to an arch dam classified as of risk type A with irrigation as the main demand associated. In the case study, a set of maximum conservation levels has been determined maximizing the supplied demand with a reliability of 90%. When accounting for initial reservoir level variability, the studied dam does not require flood control levels to fulfill the regulations regarding to overtopping. However, if the initial reservoir level at the beginning of the flood event is assumed equal to the seasonal maximum conservation level, the reservoir needs a flood control volume of 70 hm3 in one of the seasons. The methodology exposed can be useful in the analysis and prioritization of investments in hydrological safety of existing dams., [ES] El estudio presenta una metodología de carácter estocástico para la definición de Normas de Explotación optimizando tanto la explotación ordinaria como la seguridad hidrológica de la presa. Además, la metodología permite tener en cuenta la variabilidad del nivel inicial en el embalse en el momento de avenida. El caso de estudio es una presa bóveda clasificada como tipo A en función del riesgo potencial cuyo principal uso es el regadío. En el caso de estudio, se ha determinado un conjunto de resguardos que, cumpliendo la normativa relativa a niveles máximos en el embalse, maximizan la demanda máxima atendible para una garantía volumétrica del 90%. Se ha observado que al tener en cuenta la variabilidad del nivel inicial en el momento de avenida, la presa del caso de estudio no necesita resguardos para cumplir la normativa, mientras que si se supone embalse lleno el volumen de resguardo es de 70 hm3 en una de las estaciones. La metodología presentada puede ser de utilidad para el análisis y priorización de inversiones en seguridad hidrológica de presas existentes.

We identified and analysed droughts in the La Plata Basin (divided into seven sub-basins) for the current period (1961-2005) and estimated their expected evolution under future climate projections for the periods 2011-2040, 2041-2070, and 2071-2099. Future climate projections were analysed from results of the Eta Regional Climate Model (grid resolution of approximately 10 km) forced by the global climate model HadGEM2-ES over the La Plata basin, and considering a RCP4.5 emission scenario. Within each sub-basin, we particularly focused our drought analyses on croplands and grasslands, due to their economic relevance. The three-month Standardized Precipitation Evapotranspiration Index (SPEI3) was used for drought identification and characterization. Droughts were evaluated in terms of time (percentage of time from the total length of each climate scenario), space (percentage of total area), and severity (SPEI3 values) of cells characterized by cropland and grassland for each sub-basin and climate scenario. Drought-severity-area-frequency curves were developed to quantitatively relate the frequency distribution of drought occurrence to drought severity and area. For the period 2011-2040, droughts dominate the northern sub-basins, whereas alternating wet and short dry periods dominate the southern sub-basins. Wet climate spread from south to north within the La Plata Basin as more distant future scenarios were analysed, due to both a greater number of wet periods and fewer droughts. The area of each sub-basin affected by drought in all climate scenarios was highly varied temporally and spatially. The likelihood of the occurrence of droughts differed significantly between the studied cover types in the Lower Paraguay sub-basin, being higher for cropland than for grassland. Mainly in the Upper Paraguay and in the Upper Parana basins the climate projections for all scenarios showed an increase of moderate and severe droughts over large regions dedicated to crops and grasse