ABSTRACT
Most rivers in high latitudes of the northern hemisphere are covered by ice during the winter period, and this cover can influence hydraulic and morphologic characteristics of these rivers. Ice cover development introduces an additional boundarylayer on top of the river, and affects water velocity magnitude and distribution, water stage and conveyance capacity. These variations can influence sediment transport and channel morphodynamics, particularly during extreme conditions when ice-jamming and break-up can locally accelerate the flow and change velocity distribution as well as average velocity magnitude. Although the influence of ice on rivers is tremendous and clear, it is not yet well studied largely due to the difficulty and danger of river ice field studies, especially during the unstable break-up period. In the present study, we utilized acoustic instruments to measure a continuous velocity profile time series under ice cover, including during the dynamic stage of breakup. Specifically, a https://www.w3.org/1998/Math/MathML"> 1200 k H z https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9780429069246/b59e18fc-9e1d-4389-b000-a1069c1cd27e/content/eq6762.tif" xmlns:xlink="https://www.w3.org/1999/xlink"/> Teledyne RD Instruments Acoustic Doppler Current Profiler (ADCP) and a https://www.w3.org/1998/Math/MathML"> 546 k H z https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9780429069246/b59e18fc-9e1d-4389-b000-a1069c1cd27e/content/eq6763.tif" xmlns:xlink="https://www.w3.org/1999/xlink"/> ASL Multi Functional Acoustic Water Column Profiler (MFAWCP) were deployed simultaneously on the same bottom mount in the regulated Nelson River, northern Manitoba for a four-month period (March-June 2012). The ADCP measured water velocity magnitudes over the water column. The (MF-AWCP) measured variation of the ice cover thickness and helped to distinguish different ice stages from each other. We assessed temporal variation in the vertical distribution of velocity and the average velocity magnitude. The consequences of this variation on sediment transport are also evaluated based on the concentration of suspended particles estimated from the backscatter intensity of emitted sound. The results demonstrate the influence of the break-up period on average velocity magnitudes and velocity distribution in rivers. The significant increase in water velocity due to break-up occurrence is followed by high flux of suspended sediment that indicates the importance of the role of river ice in important river characteristics such as discharge, velocity and sediment transport.
