THE WORLD DELTA DATABASE

THE MACKENZIE DELTA

Delta ID    # 19.

DISCHARGE WATER 9,100 M3/S, SEDIMENT 126X106 TONS/YR,

DRAINAGE BASIN AREA 1.448X106 KM2

The Mackenzie River is the longest river in Canada, covering a distance of 1,470 km. The river originates at the Great Slave Lake in the Northwest territories and flows north in the Arctic Ocean (Figure 57). The drainage basin covers an area of 1,448,400 sq km and originates in the Canadian Shield of Canada. Most of the central drainage basin lies within the Alberta Basin. PreCambrian basement rocks are dominant in the eastern part of the basin, while Devonian and Cretaceous sedimentary rocks are found with the central part of the basin. Drainage density of the tributaries is quite high and several large rivers such as the Peace, Athabasca, Liard, and Slave are part of the drainage pattern. Average elevation in the basin is 620 m, with maximum elevations attaining a height of 2,167 m and minimum elevations of 80 m. Relief in the upper basin is quite high, average relief being 730 m. Annual average rainfall is 335 mm with a maximum of 893 mm and a minimum of 119 mm. The rainy months are July through September, when precipitation rarely falls below 30 mm. There are about 300 days during the year when the temperature is below freezing. The drainage basin is covered by Boreal forests and taiga and results in an extremely large volume of woody debris flowing down the river.

The channel in the well-defined alluvial valley is predominantly braided in nature, but meandering is present in the lower part of the valley. Average annual discharge is 8,561 m³/sec with a maximum of 18,188 m³/sec and a minimum of 2,873 m³/sec. Discharge is rather peaked because of the rapid thaw in the drainage basin and the flood season lasts from May through September during which monthly discharge generally exceeds 10,000 m³/sec. The month of March has the lowest discharge (2,873 m³/sec).

The delta has an area of 8,506 sq km and is formed in a narrow embayment of the general coast. The climate of the area is very cold, with mean temperatures of -29.6°C in January and 13.6°C in July at Inuvik (Pannatier, 1997). Much of the Mackenzie Delta is underlain by permafrost. The permafrost is approximately 100 m thick in land areas in the delta and well away from river channels or lakes. The delta is dominated by approximately 25,000 lakes [19-i02]. These lakes are not static features, but are constantly changing. Only northern deltas have such a large number of lakes, as most temperate and tropical deltas have large areas of marshes and swamps, and few lakes. The main distributary of the delta is quite complex and displays a sinuous pattern with a few meandering stretches. The delta is home to one of the world's largest concentration of pingos, with about 1,450. Pingos are large, volcano-shaped mounds of solid ice, which are thrust up through the permafrost terrain by the growth of their ice cores from below. Most of the delta plain is characterized by patterned ground or ice polygons. Tides are very low in the Arctic Ocean and spring tides are less than 0.3 m. Wave action is also relatively low, with the root mean square wave height being only 0.15 m. Drill holes reveal that there is about 70 to 80 m of deltaic sediment overlying bedrock [http://www.nwtresearch.com/simply/scirep6a.htm]. Wood found at a depth of 38 m in one of these holes was dated using radiocarbon techniques at around 6,900 years of age. This is one example of the information used to demonstrate that the delta has formed since the retreat of the continental glaciers from this area between 12,000 to 13,000 years ago [http://www.nwtresearch.com/simply/scirep6a.htm].

Net sedimentation rates on distributary channel levees vary between 1.3 and 2.3 cm/yr in the middle delta, while they range from 0.5 to 1.4 cm/yr in the outer delta (Pannatier, 1997). Lateral channel migration is limited by the development of fine grained levees covered by vegetation and stabilized by the presence of perennially frozen ground. Net sedimentation rates in lakes connected to the channel system vary between 0.36 and 1.16 g/cm^/yr in the middle delta and between 0.15 and 0.64 g/cm/yr in the outer delta.