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Abstract: Built in 1930 on the Matawin River (5770km²) to supply hydroelectric plants located downstream on the Saint-Maurice River, the Taureau Reservoir caused an inversion of the natural hydrological cycle: maximum flows occur in winter and minimum flows occur in spring during snowmelt. This inversion induces a very rapid rise of the reservoir level (base level for the channel upstream from the reservoir) in April–May during the filling-up process. The goal of the study is to analyze the effect of the rapid rise of the base level on the morphological evolution of the 7-km-long sandy section of the Matawin River located immediately upstream from the reservoir and to compare it with Jiongxin''s general model. Comparison of aerial photos taken before (1928) and after (1937, 1950, 1965, 1975, 1983, and 1995) reservoir construction reveals no significant change in the bankfull mean width, sinuosity, and bankfull depth of the studied section. It follows that the morphological evolution of the Matawin River channel upstream from the dam is not consistent with the Jiongxin model. The effect of the inverted hydrological regime in fact produces high channel stability. This stability will probably contribute to a slow but progressive reduction of the channel width and an increase of the sinuosity. This morphological evolution seems typical of the semialluvial streams found upstream from the inverted-type reservoir of the Canadian Shield. [Copyright &y& Elsevier]

Abstract: The planform geometry and migration behaviour of confined meandering rivers at 23 locations in Alberta and British Columbia are examined. Relationships among planform geometry variables are generally consistent with those described for freely meandering rivers with small but significant differences because of the unique meander pattern of confined meanders. These exceptions are the ratio channel wavelength (l)/channel width (w) and the bend curvature (r m/w); in these confined meanders, the ratios exceed (l/w ≈17; r m/w =4.1) the free-meander norms (l/w =8–14; r m/w =2–3). In general, these migrating confined meandering rivers do not develop cutoffs, and meander bends appear to migrate downstream as a coherent waveform. Migration rates vary greatly, from 0.01 to 5.8m/y, consistent with the general distribution of published rates for freely meandering rivers. Attempts to seek correlations between migration rate and channel flow and morphometry data are modestly successful. Stream power offers the best statistical predictor of migration rate, accounting for up to 52% of variance in migration rate, greater than that provided by valley slope (34%), bankfull width (32%), and mean annual flood (30%). Overall, the findings indicate that confined meandering rivers within western Canada may be more usefully regarded as part of a continuum of a meandering river pattern rather than as a unique river planform. [Copyright &y& Elsevier]

Abstract: Near-future climate change will affect the discharge and base level of rivers and thus cause channel changes. The nature and pace of such changes can be simulated using morphodynamic models. As part of an investigation of how the changing hydrology of the St-Lawrence River, Quebec, Canada, will affect its tributaries we have made additions and modifications to a one-dimensional morphodynamic model developed for gravel-bed rivers (SEDROUT). The changes allow simulation of sand-bed rivers, variable discharge, downstream water level fluctuations, and flow and sediment routing in channels with islands. A revised formulation for calculating the grain size distributions of the surface and subsurface material is presented to allow for alternating sedimentation and erosion. We test the enhanced model using small-scale simulations and present-day conditions in four tributaries of the St-Lawrence River. The model is calibrated and validated for the tributaries and the capability to simulate river morphology over a 100-year period is tested. Good validation agreement on water level, cross-sectional mean velocity, and sediment transport rate is obtained for the four tributaries of the St-Lawrence River. With these modifications, modelling a very wide range of river morphodynamic problems is now possible. [Copyright &y& Elsevier]

Abstract: The study is aimed at investigating the response of the riffle–pool sequence to increased energy expenditure in the horizontal plane through meander development. It emphasizes field measurements of riffle–pool height and spacing and their links with meander morphology. River reaches in southern Ontario (Canada) were surveyed and statistical relations were established between parameters describing riffle–pool morphology (sequence length and amplitude) and planform curvature. The results indicate a lengthening of the sequence with increased total angular deflection along the measured reaches. Further analysis suggests that this lengthening occurs in the pool as a result of meander development. Apparently, as the path length extends beyond a critical threshold for a given bed material size, the transport capacity of the sequence is compromised. This may promote an initial shortening of the downstream riffle, with depositional processes ultimately forming a new riffle slightly upstream to achieve a new equilibrium. Additional extensive data sets provided by the Toronto and Region Conservation Authority on riffle–pool morphology also suggest that bed material size plays a significant role in controlling riffle–pool morphology. [Copyright &y& Elsevier]

Abstract: A two-dimensional (2D) numerical hydrodynamic-morphological model is developed to investigate gravel transport and channel morphology in a large wandering gravel-bed river, the Fraser River Gravel Reach, in British Columbia, Canada. The model takes into count multi-fraction bedload transport, including the effects of surface coarsening, hiding and protrusion. Model outputs together with river discharge statistics were analyzed, producing distributed sediment budget and well-defined, localised zones of aggradation and degradation along the gravel reach. Long-term channel response to gravel extraction from aggrading zones as a flood hazard mitigation measure was also investigated numerically to assess the effectiveness of such an extraction. The total computed sediment budget agrees well with results based on field measurements of gravel transport available to us. This study points to the importance of a number of factors to bedload predictions: the gravel-to-sand ratio, the adequacy of resolving the wandering planform, and the distinction between bed shear stress driving bedload transport and bed resistance on the flow. These are in addition to the physical processes governing the flow field and gravel mobilization. The methodology presented in this paper can provide a scientific basis for gravel management including monitoring and extraction in order to maintain adequate flood protection and navigation, while preserving the ecosystem. [Copyright &y& Elsevier]

Abstract: Six rivers within the Miramichi basin of New Brunswick display long sections with multiple channels that surround semi-permanent islands, linked by single channels. This type of anabranching river may be termed wandering, displaying a similar planimetric pattern to wandering rivers in western Canada. This research addresses three objectives: (1) to provide a detailed description of the location, pattern characteristics and boundary conditions of wandering Miramichi rivers; (2) to compare the pattern characteristics among wandering rivers within the Miramichi basin and to other wandering, meandering and braided rivers; and (3) to investigate formative processes for wandering Miramichi rivers. Wandering rivers within the Miramichi region occur in larger valleys located downstream of an abrupt change in bedrock from resistive to more erosive bedrock lithology. Larger rivers display greater braid indices than smaller rivers. Wandering Miramichi rivers display more similarities to meandering rivers than braided rivers, exhibit an anabranching pattern, yet have characteristics markedly different from anastomosed rivers. Energy levels, mid-channel bar formation, migration rates and width–depth ratios are all within the meandering range, lower than braided and higher than anastomosed. Once anabranches are created, larger rivers apparently maintain a greater number of anabranches because of greater discharge. Wandering Miramichi rivers may represent another anabranching river pattern type, different from anastomosed and previously described wandering rivers. [Copyright &y& Elsevier]

An avulsion of the lower Saskatchewan River in the 1870s inundated a large segment of peat-covered floodplain that subsequently has become aggraded with a broad (500 km2) belt of alluvium deposited by the redirected flow. Routing of water and sediment discharge through the avulsion-affected area has been accomplished mainly by networks of sandy bedded anastomosed channels that have formed, evolved, and abandoned as the alluvial belt prograded down the floodplain slope. These processes continue today, though at a much-reduced rate. New channels, formed by crevassing and basinward extension of distributaries, are initially small and shallow, with bottom elevations situated within the avulsive alluvium but above the pre-avulsion peat (floodplain) surface. Subsequent enlargement and downcutting of many of these channels eventually uncovers the underlying peat layer whose resistance to erosion exerts significant influence on cross-sectional shape and further channel development. Peat-floored channels tend to have rectangular cross-sections, high ratios of average to maximum depth (D/Dmax), and a large range of width-to-depth ratios. If the channel continues to enlarge, the peat layer eventually becomes breached, commonly leading to temporarily irregular cross-sections caused by localized scouring at the breach sites. Eventually, the peat layer is completely eroded from the channel floor by undercutting and slumping, after which channel shape becomes governed mainly by other perimeter characteristics. Channels unaffected by peat, either before the peat layer is encountered during early channel development or after it is entirely removed, tend to have low width/depth ratios and a large range of D/Dmax values. [Copyright &y& Elsevier]

The Holocene evolution of the shallow alluvial valley occupied by the Red River was investigated at two successive river meanders near St. Jean Baptiste, Manitoba. A transect of five boreholes was sited across the flood plain at each meander to follow the path of lateral channel migration. From the cores, 24 wood and charcoal samples were AMS radiocarbon dated. The dates from the lower half of the alluvium in each core are interpreted to represent the age of the lateral accretion deposits within the flood plain at the borehole sites. The ages of these deposits increase progressively from ∼900 to 7900 and 1000 to 8100 cal years B.P. along each transect, respectively, from the proximal to distal portions of the flood plain. At the upstream meander, the average rate of channel migration was initially 0.35 m/year between ∼7900 and 7400 cal years B.P., then decreased to 0.18 m/year between ∼7400 and 6200 cal years B.P., and subsequently varied between 0.04 and 0.08 m/year. Net channel incision of the river since 8100 cal years B.P. is estimated to have ranged between 0.4 and 0.8 m/ky. The pre-6000-years-B.P. interval of greater channel migration is hypothesized to reflect a higher phase of sediment supply that was associated with the establishment of the river system on the former bed of glacial Lake Agassiz. Since 1000 years B.P., the outward migration of the meanders has caused a gradual enlarging of 0.7–2% in the cross-sectional area of the shallow valley at the two meanders. When considered proportionally over timescales of up to several centuries, the widening of the valley cross-section is very low to negligible and is deemed an insignificant factor affecting the modern flood hazard on the clay plain. [Copyright &y& Elsevier]