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The Saskatchewan River Delta (SRD) is a large alluvial delta that straddles the border between the provinces of Saskatchewan and Manitoba in south-central Canada. Currently terminating at Cedar Lake, Manitoba, the delta is composed mainly of various types of wetlands, shallow lakes, and active and abandoned river channels bordered by forested natural levees. Sixty-five percent of the delta is occupied by vegetated wetlands, over one third of which comprise peat-forming fens and bogs.〔Ducks Unlimited Canada, 2010, Analysis of wetlands in the Saskatchewan River Delta based on Pasquia Project Enhanced Wetland Classification, Edmonton Alberta.〕〔 Dirschl, H.J., 1972, Geobotanical processes in the Saskatchewan River Delta: Canadian Journal of Earth Sciences 9:1529-1549. 〕 Geographically, the SRD consists of two parts---western and eastern---separated by a prominent moraine (The Pas Moraine) that was deposited by the Laurentide Ice Sheet during late stages of the Wisconsinan glacial epoch. These two components, commonly termed the "upper delta" and "lower delta", together occupy an area of approximately making the SRD one of the largest active inland delta in North America.〔Page 129 of: (【引用サイトリンク】url=http://www.saskriverbasin.ca/page.php?page_id=70# )〕 The broad wetland tracts of the upper delta in Saskatchewan are sometimes referred to as the Cumberland Marshes.〔Smith, N.D., Cross, T.A., Dufficy, J.P., and Clough, S.R., 1989, Anatomy of an avulsion: Sedimentology 36:1-23.〕 Approximately 5% of the delta surface has been drained for agricultural use following feasibility studies by the Prairie Farm Rehabilitation Administration in the 1950s. The SRD is fed mainly by the Saskatchewan River, whose drainage basin extends westward to the continental divide and includes the eastern slopes of the Canadian Rocky Mountains and much of the high plains region of southern Alberta and Saskatchewan. The Saskatchewan River ''sensu stricto'' begins at the confluence of its two main tributaries, the North and South Saskatchewan Rivers, upstream from the head of the SRD. Approximately 80% of the flow to the delta comes from the Saskatchewan River whereas the other 20% is supplied by smaller streams that enter the SRD at its margins. These include the Torch, Mossy, Grassberry, Sturgeon-Weir, Carrot, and Pasquia Rivers. Most of the SRD is uninhabited, but approximately 15,000 people live in scattered communities around its perimeter, about two-thirds comprising Metis and First Nations peoples and one-third Euro-Canadian. Principal communities, including associated First Nations reserves, are The Pas, Moose Lake, and Cormorant (in Manitoba) and Cumberland House, Red Earth, and Shoal Lake (in Saskatchewan). Well over half of the delta population resides in and near The Pas, situated on the The Pas Moraine between the upper and lower deltas. ==Geological and human history== Like all deltas, the SRD formed by deposition of river-borne sediment into a standing body of water. Early stages of SRD development began some 10-11,000 years ago where the east-flowing Saskatchewan River entered the western shore of former Glacial Lake Agassiz, an enormous meltwater lake formed at the margins of the Laurentide Ice Sheet as it receded to the northeast.〔 Schreiner, B.T., 1983, Lake Agassiz in Saskatchewan: in Teller, J.T., and Clayton, L, (eds), Glacial Lake Agassiz, Geological Association of Canada Special Paper 26, p. 75-96.〕〔Teller, J.T., and Leverington, D.W., 2004, Glacial Lake Agassiz: a 5000 yr history of change and its relationship to the δ18O record of Greenland: Geological Society of America Bulletin 116:729-742.〕 The delta expanded eastward as the lake shallowed by glacial rebound, eventually exposing the earlier-formed The Pas Moraine between 8200 and 8700 years ago. 〔 Morozova, G.S., and Smith, N.D., 1999, Holocene avulsion history of the lower Saskatchewan fluvial system, Cumberland Marshes, Saskatchewan-Manitoba, Canada: in Smith, N.D., and Rogers, J. (eds), Fluvial Sedimentology VI, International Association of Sedimentologists Special Publication 28, p. 231-249.〕 Channel incision of the moraine followed, establishing through-flow of the Saskatchewan River and initiation of the lower delta. Growth of both the upper and lower components of the SRD has continued to the present, but now mostly by expansion of the lower delta into Cedar Lake, a remnant of Glacial Lake Agassiz, and to a lesser extent the delta of the Mossy River at Cumberland Lake north of Cumberland House. As the SRD developed through time, the principal channels of the Saskatchewan River frequently changed courses (avulsed) as part of the normal process of delta evolution. In the upper delta alone, at least nine major avulsions have occurred in the past 5,400 years.〔Morozova, G.S., and Smith, N.D., 1999, Holocene avulsion history of the lower Saskatchewan fluvial system, Cumberland Marshes, Saskatchewan-Manitoba, Canada: in Smith, N.D., and Rogers, J. (eds), Fluvial Sedimentology VI, International Association of Sedimentologists Special Publication 28, p. 231-249.〕 Remnants of these avulsions can be observed today as partly or wholly abandoned channels scattered over the delta surface. The most recent avulsion, initiated in the 1870s, has had profound effects on the physiography and ecosystems in the northwestern region of the delta.〔〔 Smith, N.D., Slingerland, R.L., Pérez-Arlucea, M., and Morozova, G.S., 1998, The 1870s avulsion of the Saskatchewan River: Canadian Journal of Earth Sciences 35: 453-466.〕 For example, Cumberland Lake, the largest lake in the SRD, has become shallower --- from pre-avulsion depths of over 6 meters to average depths of less than 1.5 meters today --- through sediment infilling following the avulsion. The 1870s event also contributed to the demise of sternwheeler riverboat traffic on the Saskatchewan River in the late 1800s and early 1900s because of difficulties in navigating through the modified channel networks resulting from the diversion.〔Peel, Bruce, 1972, Steamboats on the Saskatchewan: Prairie Books, The Western Producer, Saskatoon SK.〕 Developmental and avulsion history of the lower delta is more poorly known although evidence of multiple historical channels is apparent from aerial photographs and satellite imagery. The SRD has a substantial history of pre-European occupation,〔 Tamplin, M.J., 1977, Prehistoric occupation and resource exploitation on the Saskatchewan River at The Pas, Manitoba: PhD dissertation, University of Arizona, Tucson, AZ 〕 and it has long served as a travel corridor and location for gathering centres for aboriginal peoples.〔Meyer, D., and Thistle, P. C., 1995, Saskatchewan River rendezvous centres and trading posts: continuity in a Cree social geography: Ethnohistory 42: 403-444. 〕 Because the Saskatchewan River is a major east-west river that connects the Rocky Mountains with the Atlantic Ocean (Hudson Bay, via Lake Winnipeg and the contiguous Nelson River), the SRD saw significant traffic during the 18th and 19th centuries from European exploration, fur trading, and commerce. Cumberland House, initially established in 1774 and now the oldest continuously occupied settlement in Saskatchewan, was a major crossroads of the fur-trading routes developed by the British-based Hudson's Bay Company and the Montreal-based North West Company. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Saskatchewan River Delta」の詳細全文を読む スポンサード リンク
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