Formation, propagation, and recession of ice cover introduce a dynamic boundary layer to the top of rivers during northern winters. Ice cover affects water velocity magnitude and distribution, water level and consequently conveyance capacity of the river. In this research, total resistance, i.e., “composite resistance,” is studied for a 4 month period including stable ice cover, breakup, and open water stages in Lower Nelson River (LNR), northern Manitoba, Canada. Flow and ice characteristics such as water velocity and depth and ice thickness and condition were measured continuously using acoustic techniques. An Acoustic Doppler Current Profiler (ADCP) and Shallow Water Ice Profiling Sonar (SWIPS) were installed simultaneously on a bottom mount and deployed for this purpose. Total resistance to the flow and boundary roughness are estimated using measured bulk hydraulic parameters. A novel method is developed to calculate composite resistance directly from measured under ice velocity profiles. The results of this method are compared to the measured total resistance and to the calculated composite resistance using formulae available in literature. The new technique is demonstrated to compare favorably to measured total resistance and to outperform previously available methods.

Freshwater unionid mussels are among the most imperiled fauna in North America, and their decline has been partially attributed to sediment from anthropogenic activities. However, there remains a debate regarding the role played by sediment in mussel declines due to a lack of field and laboratory evidence. If sediment is responsible for mussel declines, then a lack of information will likely impede efforts to mitigate species declines and protect remaining habitat. However, if the impacts of sediment are overstated, time and resources may be wasted on a threat that has little bearing on mussel declines or habitat loss. Given this knowledge gap, the purpose of this paper is to review the literature focused on the potential impact of suspended sediment and sedimentation on freshwater mussels. We focused our search on suspended sediment, expressed either as suspended sediment concentration (SSC) or total suspended solids (TSS), and sediment deposition and scour. We found increases in suspended solids could impact mussels by decreasing food availability, physically interfering with filter feeding and respiration, and impeding various aspects of the mussel–host relationship. We also found mussel–sediment thresholds, wherein certain concentrations of sediment caused significant declines in population performance, which could serve as reference points for ecological research and management. Specifically, we found clearance rates (a measure of feeding) were negatively impacted by TSS concentrations >8 mg/L, and respiratory stress occurred at ∼600 mg/L. Declines in fertilization success and glochidial (i.e., mussel larvae) development were observed at TSS values of 15 mg/L, and reproductive failure occurred at 20 mg/L. Impacts on host fish attachment and glochidial encystment occurred at TSS concentrations of 1250–5000 mg/L. Impacts on fish varied depending on the biological endpoint but typically occurred at TSS values ranging from 20 to 5000 mg/L. We also found mussels were sensitive to smothering and mortality occurred at depths as low as 0.6–2.5 cm of substrate. Finally, we found relative shear stress (RSS) values >1, which is a measure of substrate stability in response to scour and entrainment, resulted in significant declines in mussel biodiversity.

The existence region plan of alternate bars, multiple bars, meandering and braiding, introduced by da Silva in 1991 and presented in its most recent form by Yalin and da Silva in the 2001 IAHR monograph Fluvial Processes, is updated and revised. For this purpose, the plan is extended by adding available laboratory and field data from the recent literature, as well as earlier data that only recently became available to the authors. Data from two series of laboratory runs conducted by the authors are also included. These were conducted to fill in a gap in the existing data, pertinent to the definition of the existence region of alternate bars. This work led to a revision to the location of the boundary lines of the existence regions of both alternate bars and meanders. An attempt was also made to reveal the existence regions of different types of multiple bars.

The 2014 Assiniboine River flood caused millions of dollars in damage to southern Manitoba and Saskatchewan. Heavy precipitation in late June and early July resulted in states of emergency being declared in both provinces as water levels reached record levels in the Upper Assiniboine Watershed, and near record levels downstream of the City of Brandon. In spite of the significant measures both provinces took to protect their citizens, the flood washed out roads and bridges and caused severe damage to properties, riverbanks and dikes. Some communities became isolated due to the flood damage to roads. Several hundred people were evacuated from homes and communities in Manitoba and Saskatchewan. The other major impact was on the farming community. The timing of this flood made it more costly than the 2011 flood from the farming perspective since most farmers had already planted their crops. The origin of the 2014 flood was different from any other major flood of the Assiniboine River since records have been kept; this was a true summer flood in that the spring freshet had already passed and flows had receded to a baseflow condition. The event was entirely due to rainfall on a basin where conditions were extremely wet and had been since before the 2011 flood. This resulted in record flows being recorded on many tributaries, and flows nearly equal to those of the 2011 event along the Assiniboine River. It should be noted that the 2011 event was initially a snowmelt event due to greater-than-normal accumulation of winter snowpack. The 2014 summer flood was “unprecedented” in the previous 130 years of observations of the Assiniboine River flows and follows only three years after the 2011 event that was described with the same adjective. The influence of anthropogenic activities, both in changing the land use and extending the drainage network, undoubtedly has played a significant role in altering prairie hydrology and potentially increasing the magnitude of flood events.