[1] In Alpine regions, especially when energy production by run-of-river plants is subsidized through state incentives, the indiscriminate growth of small plants built in cascade along the same river threatens aquatic ecosystems by depleting significant fractions of the river network. This paper compares the economic profitability of small run-of-river power plants and the ensuing hydrologic disturbance between the intake and the outflow, as resulting from the adoption of two alternative management strategies, namely the minimum flow discharge and a percent-of-flow rule. The capacity that maximizes the produced energy or the economic value of the plant, as well as the flow regime between the intake and the outflow, are analytically expressed as a function of the frequency distribution of the available streamflows. A quantitative framework relying on a set of synthetic hydrologic and economic indices is then proposed to compare the effectiveness of management strategies. The application of the method to three case studies in North-Eastern Italy evidences that the compliance of the minimum flow discharge does not prevent huge alterations of some key attributes of the flow regime, especially the temporal flow correlation. For a given and equal economic profitability of the investment, the two management strategies produce similar ecodeficits and an analogous reduction of the mean discharge between the intake and the outflow. However, the percent-of-flow strategy allows a reduced disturbance on the temporal correlation and the skewness of river discharges. Furthermore, when a percent-of-flow strategy is implemented, possible policy redefinitions aimed at reducing the hydrologic disturbance of the plant in the reach between the intake and the outflow can be complied with at reduced costs in terms of missed energy production. The framework developed may be a valuable tool to assess the ability of water management strategies to trade between hydrologic disturbance and anthropogenic uses of fresh water.Citation: Lazzaro, G., S. Basso, M. Schirmer, and G. Botter (2013), Water management strategies for run-of-river power plants: Profitability and hydrologic impact between the intake and the outflow, Water Resour. Res., 49,[8285][8286][8287][8288][8289][8290][8291][8292][8293][8294][8295][8296][8297][8298]
Intense turbidity currents occur in the Malaylay Submarine Canyon off the northern coast of Mindoro Island in the Philippines. They start in very shallow waters at the shelf break and reach deeper waters where a gas pipeline is located. The pipeline was displaced by a turbidity current in 2006 and its rock berm damaged by another 10 years later. Here we propose that they are triggered near the mouth of the Malaylay and Baco rivers by direct sediment resuspension in the shallow shelf and transport to the canyon heads by typhoon-induced waves and currents. We show these rivers are unlikely to generate hyperpycnal flows and trigger turbidity currents by themselves. Characteristic signatures of turbidity currents, in the form of bed shear stress obtained by numerical simulations, match observed erosion/deposition and rock berm damage patterns recorded by repeat bathymetric surveys before and after typhoon Nock-ten in December 2016. Our analysis predicts a larger turbidity current triggered by typhoon Durian in 2006; and reveals the reason for the lack of any significant turbidity current associated with typhoon Melor in December 2015. Key factors to assess turbidity current initiation are typhoon proximity, strength, and synchronicity of typhoon induced waves and currents. Using data from a 66-year hindcast we estimate a ~8-year return period of typhoons with capacity to trigger large turbidity currents.
Geochemical investigations carried out on submarine hydrothermal fluids vented offshore the Pontine Islands (Tyrrhenian Sea) revealed the existence of gas vents to the W of Zannone Island and SW of Ventotene Island. The geochemical features of the CO2-rich gas samples show a clear mantle-derived signature with3He/4He of 3.72-3.75 Ra and 1.33 Ra at Zannone and Ventotene, respectively. Gas geochemistry denotes how CO2-rich gases undergo fractionation processes due to CO2dissolution to a variable extent favoring enrichment in the less soluble gas species, i.e., CH4, N2, and He. The carbon isotope composition of CO2, expressed asδ13C vs. V-PDB, ranges from -0.71 and -6.16‰ at Zannone to 1.93‰ at Ventotene. Preliminary geothermometric and geobarometric estimations indicate equilibrium temperatures in the range of 150-200°C at Zannone and >200°C at Ventotene besides H2O pressures in the range of 5 bar and 20 bar at Zannone and Ventotene, respectively. Although the latest volcanic activity at the Pontine Archipelago is dated Middle Pleistocene, the combination of the new geochemical information along with geothermometric estimations indicates that cooling magmas are likely releasing enough thermal energy to form an efficient hydrothermal system.
Atlantic salmon is an economically and ecologically important fish species, whose survival is dependent on successful spawning in headwater rivers. Streamflow dynamics often have a strong control on spawning because fish require sufficiently high discharges to move upriver and enter spawning streams. However, these streamflow effects are modulated by biological factors such as the number and the timing of returning fish in relation to the annual spawning window in the fall/winter. In this paper, we develop and apply a novel probabilistic approach to quantify these interactions using a parsimonious outflux‐influx model linking the number of female salmon emigrating (i.e., outflux) and returning (i.e., influx) to a spawning stream in Scotland. The model explicitly accounts for the interannual variability of the hydrologic regime and the hydrological connectivity of spawning streams to main rivers. Model results are evaluated against a detailed long‐term (40 years) hydroecological data set that includes annual fluxes of salmon, allowing us to explicitly assess the role of discharge variability. The satisfactory model results show quantitatively that hydrologic variability contributes to the observed dynamics of salmon returns, with a good correlation between the positive (negative) peaks in the immigration data set and the exceedance (nonexceedance) probability of a threshold flow (0.3 m3/s). Importantly, model performance deteriorates when the interannual variability of flow regime is disregarded. The analysis suggests that flow thresholds and hydrological connectivity for spawning return represent a quantifiable and predictable feature of salmon rivers, which may be helpful in decision making where flow regimes are altered by water abstractions.
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