Annunziato Siviglia

In Alpine areas, the temporal patterns of hydropower plants operations can have consequences for the water bodies which receive downstream releases in the form of "hydropeaking", typically consisting in sharp releases of turbinated water in the river reaches below dams. Hydropeaking may significantly affect also the thermal regime of rivers: typically power plants fed by hypolimnetic releases from large dams cause a reduction in summer temperature and an increase in winter temperatures for long distances downstream. Very few studies have addressed the effects of the short-term temperature fluctuations related to hydropeaking (i.e., thermopeaking) on aquatic fauna, although they can be a major cause of riverine habitat degradation posing serious threats to aquatic communities. In the Adige River watershed, warm thermopeaking occurs from September to January and results in additional (up to 4°C) heating to the natural dial fluctuations; cold thermopeaking occurs from March to July and cools down the temperature (up to 6°C), in contrast with the natural trend that would result in heating during the day. The biological effects of thermopeaking are difficult to study in nature, because they are associated with hydropeaking, which is known to cause a high catastrophic drift due to the increased intensity of bed scour. However, controlled simulations of thermopeaking events could be performed in artificial flumes. We used artificial flumes which had proved to perform discharge manipulations which simulate hydropeaking events, and conducted four simulations, two warm thermopeakings in early and late winter, and two cold-thermopeakings, in early and late summer, respectively. The impact of thermopeaking on benthic macroinvertebrates was assessed by collecting those organisms which are displaced from the substrate and drift in the water column. Displacement can be active (i.e., part of the behavioural repertoire of certain insect species), or passive (i.e., catastrophic and generated by any disturbance). Drifting invertebrates were collected at time intervals before the simulation, and at continuous, short-time intervals during the simulation in order to follow the changes in drift over a short time period during the simulation. We assessed the effects of thermopreaking on the benthos community by answering to the following questions: 1) Do thermal alterations induce an increase in drift of benthic invertebrates? 3) Do a reduction or an increase in water temperature have different effects of invertebrate drift? Benthic invertebrates responded more to the cold thermopeaking simulations, with differences among taxa with different life strategies and ecological requirements.

[1] We thank Cao and Hu [2008] very much for their comment. We must honestly say that at first sight, we felt that their point, reproducing that raised by Cao and Carling [2003] to challenge the formulation of the 1-D governing equations proposed by Lisle et al.[2001], had already been proven to be erroneous by Cui et al.[2005]. However, after more careful examination of the matter, we have concluded that both the final forms of the continuity equation derived by Cao and Hu [2008](hereinafter referred to as CH) and Lanzoni et al.[ ...

Abstract A numerical solution is proposed for mud-flow propagation on sloping beds assuming the rhelogic behaviour to be modelled as a Herschel-Bulkley fluid. Novel features of the present contribution are the effect of curvature of the bottom as well as the inclu-sion of the role of entrainment of bed material by the mud-flow. Due to the nonlinear rheological characteristics of the mud-flow, a set of hyperbolic nonlinear partial dif-ferential equations are derived in conservative form which model the unsteady non uniform flow. Depth- ...

Sudden instream releases of hypolimnetic water from hydropower plants [i.e. hydropeaking (HP)] can cause abrupt temperature variations [i.e. thermopeaking (TP)], typically on a daily basis. The propagation of discharge and thermal waves is asynchronous, causing the benthic community to undergo two different but consecutive impacts. Invertebrates respond to sudden increases in discharge with catastrophic drift, and respond to sudden changes of temperature with behavioural drift. Owing to the time lag separating discharge and thermal wave peaks, catastrophic and behavioural drift can occur as distinct events. We conducted simulations in a set of open air flumes directly fed by an Alpine stream, and analysed drift induction in benthic invertebrates caused by a HP wave followed by a cold TP wave, and compared it with drift induced only by a cold TP wave. Drift propensity increased during HP and TP simulations, with a synergic effect: drift was higher when the TP wave followed the HP one. We also recorded a selective effect: some taxa did not respond to the alterations, some taxa responded to the discharge variations and to the thermal variations, or to the thermal variations alone. The most abundant taxa in benthos were Chironomidae and Baetidae, followed by Simuliidae. Simuliidae and Chironomidae were the most abundant drifting taxa. Copyright © 2012 John Wiley & Sons, Ltd.

In Alpine areas, the temporal patterns of hydropower plants operations can have consequences for the water bodies which receive downstream releases in the form of "hydropeaking", typically consisting in sharp releases of turbinated water in the river reaches below dams. Hydropeaking may significantly affect also the thermal regime of rivers: typically power plants fed by hypolimnetic releases from large dams cause a reduction in summer temperature and an increase in winter temperatures for long distances downstream. Very few studies have addressed the effects of the short-term temperature fluctuations related to hydropeaking (i.e., thermopeaking) on aquatic fauna, although they can be a major cause of riverine habitat degradation posing serious threats to aquatic communities. In the Adige River watershed, warm thermopeaking occurs from September to January and results in additional (up to 4°C) heating to the natural dial fluctuations; cold thermopeaking occurs from March to July and cools down the temperature (up to 6°C), in contrast with the natural trend that would result in heating during the day. The biological effects of thermopeaking are difficult to study in nature, because they are associated with hydropeaking, which is known to cause a high catastrophic drift due to the increased intensity of bed scour. However, controlled simulations of thermopeaking events could be performed in artificial flumes. We used artificial flumes which had proved to perform discharge manipulations which simulate hydropeaking events, and conducted four simulations, two warm thermopeakings in early and late winter, and two cold-thermopeakings, in early and late summer, respectively. The impact of thermopeaking on benthic macroinvertebrates was assessed by collecting those organisms which are displaced from the substrate and drift in the water column. Displacement can be active (i.e., part of the behavioural repertoire of certain insect species), or passive (i.e., catastrophic and generated by any disturbance). Drifting invertebrates were collected at time intervals before the simulation, and at continuous, short-time intervals during the simulation in order to follow the changes in drift over a short time period during the simulation. We assessed the effects of thermopreaking on the benthos community by answering to the following questions: 1) Do thermal alterations induce an increase in drift of benthic invertebrates? 3) Do a reduction or an increase in water temperature have different effects of invertebrate drift? Benthic invertebrates responded more to the cold thermopeaking simulations, with differences among taxa with different life strategies and ecological requirements.

Sudden instream releases of hypolimnetic water from hydropower plants (i.e. hydropeaking) can cause abrupt temperature variations (i.e. thermopeaking), typically on a daily basis. We investigated the thermopeaking effects on benthic invertebrate drift by simulating abrupt thermal shifts in experimental flumes. We conducted two cold thermopeaking and two warm thermopeaking simulations by quickly cooling the water by 3–4°C during the warm season and by warming the water by 2–3°C during the cold season at a rate of about 2.4 × 10−1°C min−1. This rate is very similar to those associated with hydropeaking waves in rivers in the same watershed as the experimental flumes. Although the achieved changes in temperature were within a tolerability range for benthic invertebrates, their drift increased threefold and fivefold, and twofold and fourfold in the two cold and two warm thermopeaking experiments, respectively. Assemblage composition of drift before and during the experiment differed, indicating that some taxa respond to abrupt thermal alterations. Larvae of Chironomidae, Simuliidae and Baetidae were the most abundant drifting taxa in all experiments during temperature alterations. The drift induced was probably behavioural, given the immediate responses of invertebrates that begun to drift within 2 min from the start of the simulations. This type of drift differs from catastrophic drift that usually occurs as a response to hydropeaking. The two types of drift can occur as distinct events in streams impacted by hydropower plants with high-elevation reservoirs and hypolimnetic releases because the propagation of the discharge and thermal waves are asynchronous, causing the benthic community to undergo two distinct but consecutive impacts. Our results suggest that the long-term effects of thermopeaking are mixed and synergical with those caused by hydropeaking and, on the long term, may alter the longitudinal distribution of benthic communities. Copyright © 2011 John Wiley & Sons, Ltd.