Persistence of a scour hole on the East Channel of the Mackenzie Delta, N.W.T.

2000 ◽  
Vol 27 (4) ◽  
pp. 798-804 ◽  
Author(s):  
Steven R Fassnacht ◽  
F Malcolm Conly
Keyword(s):  
Average Rate ◽  
Temporal Stability ◽  
Mackenzie Delta ◽  
River Channels ◽  
Channel Stability ◽  
Practical Concern ◽  
Scour Hole ◽  
Lateral Erosion ◽  
Morphologic Data ◽  
Mackenzie River

Anomalies in the bathymetry of river channels are of great practical concern for designing sub-bed pipeline crossings. Of particular interest is the long-term stability of deep holes. Bathymetric evidence indicates that one unusually deep hole in the East Channel of the Mackenzie River, referred to as a scour hole, has existed as early as 1956. Detailed hydraulic and morphologic data were first collected in 1985, and again in 1992 to assess the spatial and temporal stability of the feature. Even with a record flood on the Mackenzie River in 1988, the hole, with a maximum depth approaching 30 m, was vertically stable over the 7-year period. However, lateral erosion and sedimentation have resulted in a shift in the horizontal position of the scour hole, with a maximum horizontal erosion of approximately 2 m/a. The average rate of lateral outward movement was observed to be 0.8 m/a.Key words: Mackenzie Delta, rivers, fluvial sediment, channel stability, scour, scour hole.

scholarly journals Flow Structure and Channel Stability at the Site of a Deep Scour Hole, Mackenzie Delta, Canada

ARCTIC ◽  
2012 ◽  
Vol 65 (2) ◽  
Author(s):  
Spyros Beltaos ◽  
Bommanna G. Krishnappan ◽  
Robert Rowsell ◽  
Tom Carter ◽  
Roger Pilling ◽  
...  
Keyword(s):  
Flow Structure ◽  
Mackenzie Delta ◽  
Channel Stability ◽  
Scour Hole

Persistence of plankton in flowing water

2007 ◽  
Vol 64 (12) ◽  
pp. 1693-1702 ◽  
Author(s):  
D J Walks
Keyword(s):  
Average Rate ◽  
Flowing Water ◽  
River Channels ◽  
Flow Heterogeneity ◽  
Planktonic Food ◽  
Drift Model ◽  
Human Modification ◽  
Slow Moving ◽  
Downstream Flow ◽  
Passive Drift

Models of river plankton frequently suggest that these passively drifting communities are limited to downstream sections of larger rivers. I examine this hypothesis using a passive drift model for populations in advective environments, followed by a comparison of predicted and observed plankton populations in rivers. Under the scenario of continuous downstream drift, much of the plankton found in rivers is not predicted to occur. However, much of the observed plankton in rivers is explained through the addition of cross-channel flow heterogeneity to the model. Empirical data support the model and predict that many river plankton populations may be drifting downstream at less than 30% of the average rate of downstream flow. Plankton collections in the slower-moving edges of rivers demonstrate densities of up to 240% higher than those in adjacent midchannel flows (p = 0.009). These slow-moving areas are important habitat for river plankton and likely play a large role in planktonic food webs within rivers. These results may help explain why river productivity often decreases as a result of the loss of flow heterogeneity within river channels through human modification to landscapes.

The hydrologic regime of Mackenzie River and connection of "no-closure" lakes to distributary channels in the Mackenzie Delta, Northwest Territories

1995 ◽  
Vol 32 (7) ◽  
pp. 926-937 ◽  
Author(s):  
C. R. Burn
Keyword(s):  
Water Level ◽  
Drainage Basin ◽  
Late Summer ◽  
River System ◽  
Water Levels ◽  
Ice Thickness ◽  
Mackenzie Delta ◽  
Lake Ice ◽  
Discharge System ◽  
Mackenzie River

Mackenzie Delta lakes have been classified by the seasonal duration of their connection to Mackenzie River. "No-closure" lakes are determined on the basis of minimum summer water level. Such lakes may become disconnected from the Mackenzie in autumn or winter, as water level falls or if the sills between lakes and distributary channels are frozen through and so sealed. Water level in the central delta rises continuously after late November–early December, at first because discharge into the delta increases once the Mackenzie drainage basin has frozen over, and then as sea and channel ice thickens in the outer delta, impounding discharge. Since 1973 this seasonal increase in stage from its minimum in early December to the level on 1 April has been between 29 and 95 cm. Between 1987 and 1994, the rise in stage near Inuvik has been slightly greater than increases in lake-ice thickness (30–68 cm). Channels and lakes that are connected to the Mackenzie discharge system in December may remain connected throughout winter. A critical sill elevation for connection of such lakes to the river system is the minimum stage minus mid-December ice thickness. Recently, these elevations have been from 1.0 to 1.6 m lower than late summer water levels. Lakes with sill elevations still lower may remain connected to the Mackenzie throughout the year. In 1993-1994, only 3 of 16 "no-closure" lakes surveyed near Inuvik remained open to the Mackenzie discharge throughout winter, representing 2% of the lakes in this portion of the delta.

scholarly journals Horizontal channel development on the upper Jizera and the upper Vltava Rivers between 1938 and 2012

Geografie ◽  
2014 ◽  
Vol 119 (2) ◽  
pp. 105-125 ◽  
Author(s):  
Martin Hložek
Keyword(s):  
River Basin ◽  
Bohemian Massif ◽  
Natural Environments ◽  
River Channels ◽  
Mountain Areas ◽  
Channel Changes ◽  
Mountainous Regions ◽  
Lateral Erosion ◽  
Study Sites ◽  
Channel Development

Through the use of orthophotomaps from 1938 and 1952, this paper examines the development of horizontal channels of selected rivers in mountain areas of the Bohemian Massif. Two study sites in northern and southern part of Bohemian Massif were analysed in order to evaluate changes in river channels under similar natural conditions. Developments on the Upper Jizera River and its tributary, the Jizerka River, were investigated for the time period of 1938–2012. The Upper Vltava (Moldau) river, along with its tributaries, was studied in regards to developments taking place over the period of 1952–2012. Historical orthophotomaps were georeferenced and river banks were subsequently determined through the use of ArcGIS software. Both sites are situated in wide valleys with a low gradient, representing an exceptional relief in generally mountainous regions. Channel changes are documented via fluvial lakes, paleomeander remnants and meander cut-offs. Together with high precipitation rates in both basins, periods of extreme floodings seem to have a significant influence on channel development and transformation. Lateral erosion is somewhat less intense when compared to other rivers in similar natural environments across Central Europe. The estimated maximum lateral erosion in the Upper Jizera River basin is 0.5 m.year−1, whereas in the Vltava River basin, the lateral erosion reaches up to 1.1 m.year−1.

Modelling of three-dimensional flow velocities in a deep hole in the East Channel of the Mackenzie Delta, Northwest Territories

2007 ◽  
Vol 34 (10) ◽  
pp. 1312-1323 ◽  
Author(s):  
Bahram Gharabaghi ◽  
Chris Inkratas ◽  
Spyros Beltaos ◽  
Bommanna Krishnappan
Keyword(s):  
Shear Stress ◽  
Three Dimensional ◽  
Bed Shear Stress ◽  
Mackenzie Delta ◽  
Stress Distributions ◽  
Deep Hole ◽  
Flow Conditions ◽  
Scour Hole ◽  
Scour Holes ◽  
The Stability

The Mackenzie River has several anomalous deep scour holes in a number of river channels in its delta. Proposed gas pipeline crossings have renewed interest in studying the stability of these scour holes. The main goal of this research project was to study flow velocity and bed shear stress distributions for a 30 m deep hole in the East Channel of the Mackenzie Delta as a first step toward assessing the stability of the scour hole and the risk of its migration during various flow conditions. In this study, a three-dimensional (3D) finite element flow model, FLUENT, using the renormalization group (RNG) k-ε turbulence model (where k is the turbulent kinetic energy and ε is the turbulence dissipation rate) was set up for the scour hole and calibrated using detailed measurements of 3D flow velocities, obtained with an acoustic doppler current profiler. The numerical model was then applied to predict flow velocity and bed shear stress distributions in and around the scour hole for three flow conditions (720, 1000, and 1400 m3/s). Results indicate that two vortices are formed in the river elbow above the scour hole. As the flow rate changed, the sizes of the vortices varied. The region upstream of the hole experienced the greatest magnitudes of bed shear stress.Key words: computational fluid dynamics, finite element, bed shear stress, deep hole, flow reversal.

Ecological patterns of diatom assemblages from Mackenzie Delta lakes, Northwest Territories, Canada

2000 ◽  
Vol 78 (1) ◽  
pp. 19-33 ◽  
Author(s):  
Murray B Hay ◽  
Neal Michelutti ◽  
John P Smol
Keyword(s):  
Correspondence Analysis ◽  
Partial Least Squares Regression ◽  
Detrended Correspondence Analysis ◽  
Mackenzie Delta ◽  
Least Squares Regression ◽  
Diatom Assemblages ◽  
Hydrological Variability ◽  
Ecological Patterns ◽  
Macrophyte Growth ◽  
Mackenzie River

Sediment samples were collected from 77 lakes in the Mackenzie Delta representing a gradient of lakes from those having continual connection with the sediment-laden Mackenzie River to lakes having connection for only a couple of days every few years. Diatom assemblages in all lakes were dominated by a diverse benthic microflora, primarily from the genera Navicula and Nitzschia. Maximum relative abundance of the dominant taxon at all sites was less than 30%, and most taxa did not dominate in more than one or two lakes. Delta lake assemblages were distinct from diatom assemblages associated with other regional transects of upland tundra and forest lakes. Detrended correspondence analysis showed that nonmotile epiphytic genera, such as Cocconeis and Gomphonema, were more common in lakes having a lower influence from the Mackenzie River, reflecting the extensive macrophyte growth within these lakes. Species diversity decreased as macrophyte production increased. Taxa responses along this macrophyte production gradient were modeled using partial least squares regression. Diatoms were sensitive to the degree of river influence, and the related biological and limnological changes, suggesting assemblages can provide an indication of hydrological variability within Mackenzie Delta lakes.Key words: diatoms, detrended correspondence analysis, Mackenzie Delta, floodplain, lakes.

Postglacial Vegetation History of the Mackenzie River Basin

1987 ◽  
Vol 28 (2) ◽  
pp. 245-262 ◽  
Author(s):  
Glen M. MacDonald
Keyword(s):  
River Basin ◽  
Great Plains ◽  
Vegetation Change ◽  
Vegetation History ◽  
Mackenzie Delta ◽  
Last Deglaciation ◽  
Vegetation Development ◽  
Plant Migration ◽  
Mackenzie River Basin ◽  
Mackenzie River

AbstractThree radiocarbon-dated cores from small lakes provide pollen records of postglacial vegetation change in the central Mackenzie River basin. These data are combined with previously published records to reconstruct vegetation development from central Alberta to the Mackenzie delta. The paleoecological data demonstrate that a continuous corridor of herb-and-shrub-dominated vegetation extended between Beringia and the Great Plains of North America from deglaciaiton until about 10,000 yr B.P. The initial vegetation was replaced by spruce forests between 10,000 and 8500 yr B.P. Significant vegetation change continued until approximately 500 yr B.P. when the muskeg-dominated landscape typical of the present subarctic was established. The initial herb-and-shrub vegetation was likely a reprise of conditions which existed during earlier Pleistocene deglaciations. These conditions may have provided a favorable environment for animals adapted to nonforested vegetation and promoted migration southward from Beringia and northward from the Great Plains during the last deglaciation and earlier Pleistocene deglaciations. The sequence of postglacial vegetation change in the Mackenzie basin likely reflects a combination of climatic change, edaphic change, and plant migration patterns and interactions.

Late Eskimo Archaeology in the Western Mackenzie Delta Area

1952 ◽  
Vol 18 (1) ◽  
pp. 30-39
Author(s):  
Douglas Osborne
Keyword(s):  
New Mexico ◽  
The Arctic ◽  
Mackenzie Delta ◽  
American Philosophical Society ◽  
Delta Area ◽  
University Of New Mexico ◽  
Arctic Coast ◽  
Mackenzie River

Although the American Philosophical Society–University of New Mexico Mackenzie Valley Expedition of 1938 (Bliss, 1939, p. 365) was not primarily concerned with Eskimo archaeology, the members felt, while at the trading rendezvous Aklavik on the lower Mackenzie River, that the opportunity to run down to the Arctic coast was too obvious to be neglected. The archaeology of the Western Eskimo of the Mackenzie area has never been well studied; little, as a matter of fact, has been added since 1930 when Mathiassen wrote the introduction to his Western Eskimo report. This paper will add somewhat to a meager store of fact.

scholarly journals Monitoring ice break-up on the Mackenzie River using MODIS data

2016 ◽  
Vol 10 (2) ◽  
pp. 569-584 ◽  
Author(s):  
P. Muhammad ◽  
C. Duguay ◽  
K.-K. Kang
Keyword(s):  
Radar Data ◽  
Channel Morphology ◽  
Mackenzie Delta ◽  
Synthetic Aperture Radar Data ◽  
Modis Data ◽  
Level 3 ◽  
Ice Velocity ◽  
Break Up ◽  
Channel Constriction ◽  
Mackenzie River

Abstract. The aim of this study was to develop an approach for estimating ice break-up dates on the Mackenzie River (MR) using more than a decade of MODIS Level 3 500 m snow products (MOD/MYD10A1), complemented with 250 m Level 1B radiance products (MOD/MYD02QKM) from the Terra and Aqua satellite platforms. The analysis showed break-up began on average between days of year (DOYs) 115 and 125 and ended between DOYs 145 and 155 over 13 ice seasons (2001–2013), resulting in an average melt duration of ca. 30–40 days. Thermal processes were more important in driving ice break-up south of the MR confluence with the Liard River, while dynamically driven break-up was more important north of the Liard. A comparison of the timing of ice disappearance with snow disappearance from surrounding land areas of the MR with MODIS Level 3 snow products showed varying relationships along the river. Ice-off and snow-off timing were in sync north of the MR–Liard River confluence and over sections of the MR before it enters the Mackenzie Delta, but ice disappeared much later than snow on land in regions where thermal ice break-up processes dominated. MODIS observations revealed that channel morphology is a more important control of ice break-up patterns than previously believed with ice runs on the MR strongly influenced by channel morphology (islands and bars, confluences and channel constriction). Ice velocity estimates from feature tracking were able to be made in 2008 and 2010 and yielded 3–4-day average ice velocities of 1.21 and 1.84 m s−1 respectively, which is in agreement with estimates from previous studies. These preliminary results confirm the utility of daily MODIS data for monitoring ice break-up processes along the Mackenzie River. The addition of optical and synthetic aperture radar data from recent and upcoming satellite missions (e.g. Sentinel-1/2/3 and RADARSAT Constellation) would improve the monitoring of ice break-up in narrower sections of the MR.

Stratigraphic, isotopic, and mineralogical evidence for an early Holocene thaw unconformity at Mayo, Yukon Territory

1986 ◽  
Vol 23 (6) ◽  
pp. 794-803 ◽  
Author(s):  
C. R. Burn ◽  
F. A. Michel ◽  
M. W. Smith
Keyword(s):  
Oxygen Isotope ◽  
Average Rate ◽  
Climatic Conditions ◽  
Yukon Territory ◽  
Mackenzie Delta ◽  
Delta Area ◽  
The Holocene ◽  
Oxygen Isotope Ratios ◽  
Abrupt Changes ◽  
Mineralogical Evidence

Ice-rich glaciolacustrine sediments near Mayo, Yukon Territory, reveal a thaw unconformity in the form of truncated ice wedges and abrupt changes in cryotexture. The unconformity has been radiocarbon dated at 8870 ± 200 years BP, which is within the Holocene period of optimal climatic conditions in northern Yukon and the Mackenzie Delta area reported by other workers. Analysis of the mineralogy of the sediments indicates that the material above the unconformity is enriched in minerals that are the products of a more intense weathering environment than those deeper in the profile. Oxygen-isotope ratios of ground ice in the sediments suggest the presence of two genetically distinct ice units above and below the unconformity. An average rate of upward permafrost growth in this area of 0.1–0.2 mm year−1 is calculated for the period since the climatic optimum.

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