{"id":599,"date":"2019-06-11T14:51:51","date_gmt":"2019-06-11T14:51:51","guid":{"rendered":"https:\/\/opentextbc.ca\/physicalgeology2ed\/chapter\/13-4-stream-types\/"},"modified":"2021-12-08T18:21:53","modified_gmt":"2021-12-08T18:21:53","slug":"13-4-stream-types","status":"publish","type":"chapter","link":"https:\/\/opentextbc.ca\/physicalgeology2ed\/chapter\/13-4-stream-types\/","title":{"raw":"13.4 Stream Types","rendered":"13.4 Stream Types"},"content":{"raw":"Stream channels can be straight or curved, deep and slow, or rapid and choked with coarse sediments. The cycle of erosion has some influence on the nature of a stream, but there are several other factors that are important.\r\n\r\n[caption id=\"attachment_592\" align=\"alignright\" width=\"450\"]\"\"<\/a> Figure 13.4.1 The Cascade Falls area of the Kettle River, near Christina Lake, B.C. This stream has a step-pool morphology and a deep bedrock channel.[\/caption]\r\n\r\n[pb_glossary id=\"1741\"]Youthful streams[\/pb_glossary]<\/strong> that are actively down-cutting their channels tend to be relatively straight and are typically ungraded (meaning that rapids and falls are common). As shown in Figures 13.0.1 and 13.4.1, youthful streams commonly have a [pb_glossary id=\"1742\"]step-pool[\/pb_glossary]<\/strong> morphology, meaning that the stream consists of a series of pools connected by rapids and waterfalls. They also have steep gradients and steep and narrow V-shaped valleys\u2014in some cases steep enough to be called canyons.\r\n\r\nIn mountainous terrain, such as that in western Alberta and B.C., steep youthful streams typically flow into wide and relatively low-gradient U-shaped glaciated valleys. The youthful streams have high sediment loads, and when they flow into the lower-gradient glacial valleys where the velocity isn\u2019t high enough to carry all of the sediment\u00a0[pb_glossary id=\"1743\"]braided[\/pb_glossary]<\/strong> patterns develop, characterized by a series of narrow channels separated by gravel bars (Figure 13.4.2).\r\n\r\n[caption id=\"attachment_593\" align=\"aligncenter\" width=\"800\"]\"\"<\/a> Figure 13.4.2 The braided channel of the Kicking Horse River at Field, B.C.[\/caption]\r\n\r\n[caption id=\"attachment_594\" align=\"alignright\" width=\"600\"]\"\"<\/a> Figure 13.4.3 The braided channel of Meager Creek in the Mt. Meager area[\/caption]\r\n\r\nBraided streams can develop anywhere there is more sediment than a stream is able to transport. One such environment is in volcanic regions, where explosive eruptions produce large amounts of unconsolidated material that gets washed into streams. Streams in the volcanic Mt. Meager area of southwestern British Columbia are good examples of this (Figure 13.4.3).\r\n\r\nA stream that occupies a wide, flat flood plain with a low gradient typically carries only sand-sized and finer sediments and develops a sinuous flow pattern. As you saw in Figure 13.3.1, when a stream flows around a corner, the water on the outside has farther to go and tends to flow faster. This leads to erosion of the banks on the outside of the curve, deposition on the inside, and formation of a point bar (Figure 13.4.4). Over time, the sinuosity of the stream becomes increasingly exaggerated, and the channel migrates around within its flood plain, forming a [pb_glossary id=\"1744\"]meandering[\/pb_glossary]<\/strong> pattern.\r\n\r\n[caption id=\"attachment_595\" align=\"aligncenter\" width=\"600\"]\"\"<\/a> Figure 13.4.4 The meandering channel of the Bonnell Creek, Nanoose, B.C. The stream is flowing toward the viewer. The sand and gravel point bar must have formed when the creek was higher and the flow faster than it was when the photo was taken.[\/caption]\r\n\r\nA well-developed meandering river is shown in Figure 13.4.5. The meander in the middle of the photo has reached the point where the thin neck of land between two parts of the channel is about to be eroded through. When this happens, another [pb_glossary id=\"1745\"]oxbow[\/pb_glossary]<\/strong> lake will form like the others in the photo.<\/a>\r\n\r\n[caption id=\"attachment_596\" align=\"aligncenter\" width=\"600\"]\"\"<\/a> Figure 13.4.5 The meandering channel of the Nowitna River, Alaska. Numerous oxbow lakes are present and another meander cutoff will soon take place. [Image Description]<\/a>[\/caption]\r\n
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Exercise 13.4 Determining stream gradients<\/p>\r\n\r\n<\/header>\r\n

\r\n\r\n[caption id=\"attachment_597\" align=\"alignright\" width=\"450\"]\"\"<\/a> Figure 13.4.6 Elevations on Priest Creek at Kelowna, BC.[\/caption]\r\n\r\nGradient is the key factor controlling stream velocity, and of course, velocity controls sediment erosion and deposition. This map shows the elevations of Priest Creek in the Kelowna area. The length of the creek between 1,600 metres and 1,300 metres elevation is 2.4 kilometres, so the gradient is 300\/2.4 = 125 metres per kilometre.\r\n
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  1. Use the scale bar to estimate the distance between 1,300 metres and 600 metres and then calculate that gradient.<\/li>\r\n \t
  2. Estimate the gradient between 600 and 400 metres.<\/li>\r\n \t
  3. Estimate the gradient between 400 metres on Priest Creek and the point where Mission Creek enters Okanagan Lake.<\/li>\r\n<\/ol>\r\nSee Appendix 3 for Exercise 13.4 answers<\/a>.\r\n\r\n<\/div>\r\n<\/div>\r\nAt the point where a stream enters a still body of water\u2014a lake or the ocean\u2014sediment is deposited and a delta forms. The Fraser River has created a large delta, which extends out into the Strait of Georgia (Figure 13.4.7). Much of the Fraser delta is very young in geological terms. Shortly after the end of the last glaciation (10,000 years ago), the delta did not extend past New Westminster. Since that time, all of the land that makes up Richmond, Delta, and parts of New Westminster and south Surrey has formed from sediment from the Fraser River. (You can see this in more detail at Geoscape Vancouver<\/a>.)\r\n\r\n[caption id=\"attachment_598\" align=\"aligncenter\" width=\"800\"]\"\"<\/a> Figure 13.4.7 The delta of the Fraser River and the plume of sediment that extends across the Strait of Georgia. The land outlined in red has formed over the past 10,000 years.[\/caption]\r\n

    Image Descriptions<\/h3>\r\n<\/a>Figure 13.4.5 image description:<\/strong> A part of the Nowitna River has curved around so sharply that it almost forms a circle before curving the other way again. Eventually, as the barrier between these two parts of the channel erodes, they will be joined and form an oxbow lake. [Return to Figure 13.4.5]<\/a>\r\n

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