Home Research Interest Research Area Publications Courses Taught My family

¡¡

1996. M.Sc., 260 pp. 

EROSION, SEDIMENTATION AND STREAM MODIFICATION DOWNSTREAM FROM A HYDROELECTRIC DAM: MATTAGAMI RIVER, NORTHERN ONTARIO

Mosher S.L.

Mosher.jpg (25467 ×Ö½Ú)The geometry, flow and sediment transport patterns at the confluence of the Mattagami River and Adam Creek have been analysed with emphasis on studying the development of coarse-grained gravel bars formed at and just below the confluence area. The gravel bars consisting of a junction bar and three alternating side bars, formed as a result of flow regulation of the Mattagami River and diversion of water through Adam Creek.
    The Mattagami River and Adam Creek are part of the Moose River drainage basin, which flow northward, emptying into James Bay. Hydroelectric dams were built on the Mattagami River by Ontario Hydro in 1963 at locations on the Precambrian Shield rear the boundary with the Hudson Bay Lowlands. The southernmost of these dams has a headpond to store water for dam use. When the ice and snow are melting during spring freshet, the headpond is not able to contain the excess water that has to be diverted through an emergency spillway, Adam Creek. The creek rejoins the Mattagami River, 34 km downstream, 17 km below the last dam.
      During the spring, a large volume of water is rerouted through Adam Creek each year, up to 4500 m3/s. The banks of the last 13 km of Adam Creek are composed of Pleistocene till and other soft sediments of the Hudson Bay Lowland and so they are subject to erosion. To date it has been estimated that over 52 million m3 of sediment has been eroded from the creek. Approximately 2.5 million m3 of that material is deposited at the junction in the four gravel bars consisting predominantly of coarse material: cobbles and pebbles with lesser boulders and sand. Such coarse material comprises less than 5 % of the total volume of material eroded from the creek. The remaining 47.5 million m3 of sand and finer material is transported further downstream.  
      
The main body of the gravel bars is believed to have formed during the first few large floods following river impoundment and spillway use when enormous amounts of erosion occurred along the Adam Creek spillway. Since then, various sections of the bars have been reactivated by subsequent floods, and have undergone numerous cycles of erosion and redeposition. Presently, the junction bar is lobate in form and is comprised of three large chutes that funnel flow from Adam Creek into the Mattagami River. The first two side bars are very similar in form. Both bars have an older section of the bar now seldom inundated, secondary chutes with chutes bars terminating onto the upstream section of the bars, a side channel separating the bar from inner bank, and a lower bar area which is reactivated more frequently than the higher older section. The third side bar slightly differs in that it is much lower in elevation and contains slightly finer sediments.  
      
The alternating pattern of the gravel bars developed because of the formation of low velocity, flow separation zones, within the confluence area modifying this reach of the Mattagami River from a long wavelength, meandering channel to a shorter wavelength, deeper thalweg bounded by the gravel bars.

¡¡

[Home] [Books] [Papers] [Reports] [Conference Papers] [Supervised Theses] [Others]