Normand E. Bergeron

Response of the Ha! Ha! River to the flood of July 1996 in the Saguenay region of Quebec: Large‐scale avulsion in a glaciated valley

Modifications to valley form due to extreme flooding in the lower 34 km of the Ha! Ha! River were analyzed. Heavy regional precipitation in July 1996 triggered extreme runoff and the catastrophic drainage of Ha! Ha! Lake, producing discharges of 1100 m3/s, 8 times the 100-year flood. Dominant valley modifications, revealed by comparing preflood and postflood topographies derived photogrammetrically, were related to two large-scale avulsions; in particular, a deep retrogressive incision which bypassed the 30-m-high Perron Falls, exporting 6 × 106 m3 of glacial stratified drift from a 2-km section of valley and producing massive sedimentation in the reach downstream. Reconstructed maximum flow power values support the existence of a 300 W/m2 threshold for major scouring of the alluvial valley bottom. The evidence highlights the potential for massive scour and fill and reorganization of the long profile, with potentially catastrophic effects on infrastructure, during extreme floods in glaciated valley settings.

Cost-effective non-metric close-range digital photogrammetry and its application to a study of coarse gravel river beds

Digital photogrammetry is now increasingly recognized as being a powerful tool in geomorphology. However, the high material costs and skills required by digital photogrammetry may deter non-photogrammetrists from using this technique in their research. This paper demonstrates the use of a close-range digital photogrammetric methodology accessible to non-photogrammetrists and yet capable of yielding good quality topographic information on coarse gravel riverbeds at minimal cost. Digital Elevation Models (DEMs) were derived from 1:165 scale imagery obtained with a 35 mm film SLR camera, a commercial desktop scanner and a softcopy photogrammetry package. Quality assessment based upon independent checkpoints and scaling analysis showed that the precision of the DEMs was consistently less than 10% of the D 50 of the bed particles. This translates into sub-centimetric precision. Whilst photogrammetry is presently capable of a better data quality at this scale, quality must be judged with respect to the requirements of the geomorphological applications under consideration. Thus, the methodological simplifications adopted in this research are acceptable in order to make photogrammetry both cost-effective and accessible.

The effect of bedload transport on mean and turbulent flow properties

Abstract This paper reports the results of a flume experiment that was designed to investigate the effect of bedload transport on mean and turbulent properties of the flow. The experiment consisted of varying the bedload transport rate for a given hydraulic condition, and of measuring the flow velocity profiles using an Acoustic Doppler Velocimeter (ADV) for each transport rate in order to allow for comparison. Bedload transport was produced by injecting gravel-size particles (D50=7.4 mm) with a conveyer belt mounted at the upstream end of the flume. The results indicate that the effect of bedload on flow characteristics is complex. It is shown that bedload transport causes opposite effects on flow velocity depending on the roughness of the bed and the relative magnitude of flow and sediment transport variables. A better understanding of these conflicting results is obtained from the application of an energy budget approach to the analysis of velocity data. This approach demonstrates that bedload affects flow velocity by modifying the rate of dissipation of turbulent kinetic energy. However, the mechanisms responsible for the modification of turbulent dissipation are still unknown.

Scale-space analysis of stream-bed roughness in coarse gravel-bed streams

This paper shows the usefulness of the scale-space filtering technique for the analysis of stream-bed roughness. In the first part of the paper, the scale-space filtering technique originally developed for signal analysis is adapted for the analysis of stream-bed microtopographic profiles. The modified technique provides a multiscale description of bed profiles, which allows the objective identification and measurement of individual roughness elements at all scales of observation. These bed elements then are classified as either grain or form roughness elements according to the roughness scales identified from a semivariogram analysis of the bed profile. Roughness indices describing each roughness scale are obtained by calculating the mean height and spacing of the grain and form roughness elements. Because they measure directly the geometry of the bed, these indices provide a better description of stream-bed roughness than the traditional method based on a single grain index. In the second part of the paper, the technique is applied to the analysis of stream-bed roughness and resistance to flow of nine different gravel-bed stream reaches. The roughness indices calculated from this approach are used to obtain predicted values of resistance to flow which are in good agreement with the values observed in the field. The quality of this prediction is compared to the one obtained from a traditional description of bed roughness based on a single grain-size index. The results indicate that the values of resistance to flow calculated using the traditional approach are significantly less accurate than the values calculated using the new procedure which separates stream-bed roughness into a grain and a form component.

Development of a flatbed passive integrated transponder antenna grid for continuous monitoring of fishes in natural streams

This paper describes a flatbed antenna grid designed for continuous remote monitoring of fish tagged with 23 mm passive integrated transponder (PIT) tags in a natural stream with extensive spatial coverage. A range of applications of the system is presented.

The effect of sediment concentration on bedload roughness

Bedload roughness is the roughness produced by sediment transported near the bed. While it is well established that the magnitude of this roughness is proportional to the thickness of the moving sediment layer, the effect of sediment concentration remains largely unknown. This paper presents the results of a flume experiment that was designed to investigate the effect of sediment concentration on bedload roughness. The experiment consisted of creating flow conditions where bedload transport is supply-limited and injecting gravel size particles (D 50 = 7.4 mm) at the upstream end of the flume in order to produce bedload transport. While keeping flow conditions constant, sediment concentration was varied by successively increasing the injection rate of gravel in the flow. For each injection rate, flow velocity profiles were measured in order to evaluate changes of mean flow velocity U, shear velocity u * , roughness length z 0 and resistance to flow f. The results indicate that low sediment concentration affects mainly the near bed portion of the flow where it causes a reduction of mean flow velocity and an increase of shear velocity and roughness length. For larger sediment concentration, the whole flow velocity profile becomes affected by bedload roughness but the importance of this effect always remain larger near the bed. As sediment concentration is augmented, mean flow velocity is consistently reduced but shear velocity and roughness length increase until a plateau is reached where these two variables become constant.

NSERC's HydroNet: A National Research Network to Promote Sustainable Hydropower and Healthy Aquatic Ecosystems

Abstract NSERCs HydroNet is a collaborative national five-year research program initiated in 2010 involving academic, government, and industry partners. The overarching goal of HydroNet is to improve the understanding of the effects of hydropower operations on aquatic ecosystems, and to provide scientifically defensible and transparent tools to improve the decision-making process associated with hydropower operations. Multiple projects are imbedded under three themes: 1) Ecosystemic analysis of productive capacity offish habitats (PCFH) in rivers, 2) Mesoscale modelling of the productive capacity offish habitats in lakes and reservoirs, and 3) Predicting the entrainment risk of fish in hydropower reservoirs relative to power generation operations by combining behavioral ecology and hydraulic engineering. The knowledge generated by HydroNet is essential to balance the competing demands for limited water resources and to ensure that hydropower is sustainable, maintains healthy aquatic ecosystems and a vibr...

Winter geomorphological processes in the Sainte-Anne River (Québec) and their impact on the migratory behaviour of Atlantic tomcod (Microgadus tomcod)

Knowledge of the migratory pattern of the Atlantic tomcod (Microgadus tomcod) towards its spawning site is scanty and controversial. This situation is partly a result of the fact that the migration takes place during winter, a period when it is difficult to investigate the relationships between flow dynamics, habitat and fish behaviour. The data reported in this paper suggest that channel morphology and flow dynamics, controlled both by the tidal regime and the ice cover, influence the migratory behaviour of the Atlantic tomcod population of the Sainte-Anne River (Sainte-Anne-de-La-Perade, Quebec). Measurements of channel morphology and flow velocity at low water indicate that the formation of ice cover in winter, combined with the presence of sand bars near the confluence of the Sainte-Anne with the Saint-Laurent River, causes a decrease in the cross-sectional area of the channel. This reduction in area is compensated for by an increase in flow velocity at the mouth of the river, where velocities larger than 30 cm/s were measured at low water. Underwater video observations of tomcod movements in the Sainte-Anne River indicate that such flow velocities limit access of upstream migrating fish to the spawning site. The data demonstrate that upstream fish migrants avoid the downstream flow velocities occurring during the falling tide and favour the short period of flow reversal associated with large rising tides in order to move upstream.

Effect of discharge and habitat type on the occurrence and severity of Didymosphenia geminata mats in the Restigouche River, eastern Canada: Effect of discharge and habitat type on the severity of D. geminata

Centre Eau Terre Environnement, Institut National de la Recherche Scientifique, 490 de la Couronne, Québec G1K 9A9, Canada School of Geography, Earth and Environmental Sciences, University of Birmingham, Birmingham B15 2TT, UK Correspondence Carole‐Anne Gillis, Centre Eau Terre Environnement, Institut National de la Recherche Scientifique, 490 de la Couronne, Québec G1K 9A9, Canada. Email: gilliscaroleann@hotmail.com