Bypass Channel (bypass + channel)

Distribution by Scientific Domains


Selected Abstracts


Efficiency of a nature-like bypass channel for sea trout (Salmo trutta) ascending a small Danish stream studied by PIT telemetry

ECOLOGY OF FRESHWATER FISH, Issue 3 2003
K. Aarestrup
Abstract , Upstream passage of adult sea trout (Salmo trutta) in a nature-like bypass channel was investigated in the Tirsbęk brook, Denmark, in autumn and winter 1999/2000. Sea trout were caught by electrofishing up- and downstream of the weir at which the bypass was situated. Fish were tagged with passive integrated transponder (PIT) tags and released downstream of the weir. Automatic PIT-tag logging stations were positioned downstream, in the lower part, and at the upstream exit of the bypass to investigate the passage success of the fish. The bypass was neither size- nor sex-selective in the size ranges investigated. The majority (68%) of fish approached the bypass at night. Over 90% of tagged upstream-searching fish located and entered the bypass channel, but only about half of them passed through. The inefficiency is suggested to be because of a combination of the length of the bypass channel and inadequate flow in the bypass channel. [source]


Efficacy of a nature-like bypass channel in a Portuguese lowland river

JOURNAL OF APPLIED ICHTHYOLOGY, Issue 5 2005
J. M. Santos
Summary Throughout Europe in the last decade there has been a steady shift away from more technical fish pass designs to more nature-like passes, such as nature-like bypass channels. Upstream fish passage in a nature-like bypass channel was investigated in a lowland river, the Lima River, for 117 days from March 2000 to May 2002. Fish passage was recorded using an automatic video recording system. Electrofishing samples within the bypass and below the weir were compared with species abundance found on the tape recordings. More than 7500 individuals of eight species passed through the bypass channel. Species composition was dominated by striped mullet (65.3%) and potamodromous species (34.3%), which used the bypass mainly at night. Of the environmental variables considered, bypass discharge explained most of the variation in the number of cyprinids, whereas water temperature was more important for diadromous species. Comparing species composition below the weir using passage recordings provided a useful tool to assess species efficacy of the bypass, although biological requirements should also be taken into account. This study proved the efficacy of the bypass for passage of almost all occurring species and life stages and also for providing suitable habitat for fish fauna, highlighting the use of these facilities for river restoration schemes. [source]


Assessing adult Trichoptera communities of small streams: a case study from Charnwood Forest, Leicestershire, UK

AQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, Issue 2 2001
M.T. Greenwood
Abstract 1.,Adult caddisflies were collected using non-attracting Malaise traps at four sites on a small headwater stream from May to November 1990. Sites S1 and S2 were most natural and upstream of a reservoir; where S3 was located in the bypass channel, and S4, downstream. 2.,The flight period for each species is recorded to provide baseline data. Flight activity patterns fall into two groupings: (a) species with a flight activity of 3,4 months, and (b) those species with a short flight period of up to 6 weeks. 3.,Sixty-one species from 15 families were collected, including the endangered Red Data Book species Tinodes pallidulus McLachlan. 4.,Significant differences in community parameters are shown among all sites, many species apparently having local catchment areas. The influence of artificial habitats, the open bypass channel and adjacent reservoir, is clearly demonstrated. 5.,The data illustrate the potential of using adult caddisflies in conservation assessment of small streams. Working with adults is taxonomically rigorous and they are useful bioindicators of the environmental quality of the valley floor corridor. Copyright © 2001 John Wiley & Sons, Ltd. [source]


Grazing impact and phenology of the freshwater sponge Ephydatia muelleri and the bryozoans Plumatella emarginata and Fredericella sultana under experimental warming

FRESHWATER BIOLOGY, Issue 5 2009
ANDREAS VOHMANN
Summary 1.,Both the clearance rates (CR) and abundances of the freshwater sponge Ephydatia muelleri and the bryozoans Plumatella emarginata and Fredericella sultana were investigated from autumn to spring under different temperature regimes. The experiments were performed in bypass channels of the River Rhine (Cologne, Germany) in which temperature could be manipulated. 2.,The impact of temperature increase on CRs depends upon the grazer: E. muelleri showed a clear increase in CRs with increasing temperature whereas P. emarginata was not significantly affected by experimental warming. 3.,Distinct differences in food preference were found for the sponge (which is an efficient grazer of bacteria and small algae) and for the bryozoan P. emarginata (which feeds primarily on large algae, and with no significant grazing on bacteria). 4.,In contrast to their temperature-related patterns in CR, respiration of both P. emarginata and E. muelleri increased with temperature between 19 and 32 °C, suggesting that the risk of experiencing energy deficiency at high temperatures due to increased metabolic rates is particularly high for the bryozoan. 5.,A temperature elevation of 3 °C above the natural Rhine temperature resulted in a delay in the disappearance of active tissue and formation of resting stages for E. muelleri in autumn. This delay ranged from 8 (beginning of gemmulation) to 22 days (termination of gemmulation). In contrast, there was no distinct effect of warming on the disappearance of active zooids of the two bryozoan species in autumn. However, warming can positively affect the maintenance of active zooids during winter in F. sultana. In spring, the appearance of active zooids of P. emarginata was clearly stimulated by temperature elevations, whereas the hatching of both F. sultana and E. muelleri was hardly affected by warming. 6.,The study demonstrated different patterns in the thermal ecology of the two freshwater bryozoans and the sponge in comparison to other filter feeders, particularly mussels. Such patterns need to be considered when predicting the impact of temperature on pelagic-benthic coupling in aquatic habitats. [source]


Efficacy of a nature-like bypass channel in a Portuguese lowland river

JOURNAL OF APPLIED ICHTHYOLOGY, Issue 5 2005
J. M. Santos
Summary Throughout Europe in the last decade there has been a steady shift away from more technical fish pass designs to more nature-like passes, such as nature-like bypass channels. Upstream fish passage in a nature-like bypass channel was investigated in a lowland river, the Lima River, for 117 days from March 2000 to May 2002. Fish passage was recorded using an automatic video recording system. Electrofishing samples within the bypass and below the weir were compared with species abundance found on the tape recordings. More than 7500 individuals of eight species passed through the bypass channel. Species composition was dominated by striped mullet (65.3%) and potamodromous species (34.3%), which used the bypass mainly at night. Of the environmental variables considered, bypass discharge explained most of the variation in the number of cyprinids, whereas water temperature was more important for diadromous species. Comparing species composition below the weir using passage recordings provided a useful tool to assess species efficacy of the bypass, although biological requirements should also be taken into account. This study proved the efficacy of the bypass for passage of almost all occurring species and life stages and also for providing suitable habitat for fish fauna, highlighting the use of these facilities for river restoration schemes. [source]