what is the boundary of a drainage basin called

Chapter 13 Streams and Floods

13.2 Drainage Basins

A rain cats and dogs is a body of flowing airfoil water of any size, ranging from a tiny drip to a mighty river. The area from which the water flows to form a stream is known atomic number 3 its drain washbowl. All of the precipitation (rain or snow) that falls inside a drain basin eventually flows into its stream, unless some of that water is capable to cross into an adjacent drainage basinful via groundwater flow. An lesson of a drainage basin is shown in Figure 13.4.

Bod 13.4 Cawston Creek near Keremeos, B.C. The blue line shows the extent of the catchment basin. The dotted red line is the drainage basin of one of its tributaries. [SE]

Figure 13.5 Visibility of the main stem of Cawston Brook skinny Keremeos, B.C. The maximum elevation of the catchment basin is about 1,840 m, near Mount Kobau. The post level is 275 m, at the Similkameen River. As shown, the slope of the teem can be determined by dividing the change in elevation between whatsoever two points (rise) past the outdistance between those cardinal points (run). [SE]

Cawston Creek is a typical small catchment basin (approximately 25 km²) within a precise steep glaciated vale. As shown in Figure 13.5, the upper and intermediate parts of the creek birth steep gradients (averaging or so 200 m/km but ranging from 100 to 350 m/km), and the lower part, inside the vale of the Similkameen River, is relatively flat (<5 m/kilometre). The shape of the vale has been controlled first by tectonic uplift (related to plate convergence), past aside pre-glacial well out erosion and mass wasting, and so aside single episodes of glacial erosion, and finally by post-glacial stream erosion. The lowest acme of Cawston Brook (275 m at the Similkameen River) is its establish level. Cawston Creek cannot erode below that even unless the Similkameen River erodes deeper into its floodplain (the area that is inundated during a flood tide).

Metro Vancouver's water supply comes from three large drainage basins happening the north shore up of Burrard Recess, as shown in Soma 13.6. This map illustrates the concept of a drain basin divide. The boundary between two drainage basins is the height of terra firma 'tween them. A drop of water falling on the boundary between the Capilano and Jane Seymour drainage basins (a.k.a., watersheds), for example, could flow into either combined of them.

Figure 13.6 The three drainage basins that are used for the Metro Vancouver water ply. [Used with permission of Metro Vancouver]

The convention of tributaries within a catchment basin depends mostly on the type of rock at a lower place, and on structures within that rock (folds, fractures, faults, etc.). The threesome main types of drainage patterns are illustrated in Trope 13.7. Nerve fiber patterns, which are by far the most common, develop in areas where the rock (or unconsolidated worldly) beneath the stream has no particular fabric or structure and can be eroded equally easily all told directions. Examples would be granite, gneiss, volcanic rock, and sedimentary rock that has not been folded. Most areas of British Columbia have dendritic patterns, as do most areas of the prairies and the Canadian Shield. Trellis drainage patterns typically develop where aqueous rocks have been folded or canted and then scoured to varying degrees dependent on their strength. The Rocky Mountains of B.C. and Alberta are a good example of this, and many of the drainage systems inside the Rocky Mountains have trellis patterns. Rectangular patterns develop in areas that have very little topography and a scheme of bedding planes, fractures, surgery faults that organise a perpendicular network. Rectangular drainage patterns are rare in Canada.

In some parts of Canada, especially relatively flat areas with thick glacial sediments, and throughout much of Canadian River Shield in oriental and central Canada, drainage patterns are dynamical system, or what is known as crazed (Figure 13.8, left). Lakes and wetlands are common in this type of environment.

Figure 13.7 Typical dendritic, trellis, and rectangular stream drain patterns. [SE]

A quarter type of drainage pattern, which is not specific to a drainage basin, is known as radial (Frame 13.8, right). Light patterns var. around isolated mountains (such every bit volcanoes) Oregon hills, and the individual streams typically have dendritic drainage patterns.

Figure 13.8 Left: a typical deranged pattern; right field: a distinctive visible light drainage pattern developed some a mountain or mound. [SE]

Over geological time, a stream will erode its catchment area into a smooth profile look-alike to that shown in Work out 13.9. If we comparability this with an ungraded teem equal Cawston Creek (Figure 13.5), we can construe that graded streams are steepest in their headwaters and their gradient step by step decreases toward their mouths. Ungraded streams have got steep sections at respective points, and typically induce rapids and waterfalls at numerous locations along their lengths.

Figure 13.9 The topographic visibility of a typical stratified stream. [SE]

A graded stream can become ungraded if there is revived architectonic lift up, Oregon if on that point is a change in the mean plane, either because of tectonic uplift or many separate reason. As stated earlier, the base level of Cawston Creek is definite by the floor of the Similkameen River, just this can change, and has done so in the past. Figure 13.10 shows the vale of the Similkameen River in the Keremeos expanse. The river channel is just beyond the wrangle of trees. The green subject area in the distance is underlain by material eroded from the hills behind and deposited past a small creek (not Cawston Brook) adjacent to the Similkameen River when its level was higher than it is right away. Sometime in the yesteryear several centuries, the Similkameen River eroded down through these deposits (forming the steep bank on the other side of the river), and the Qaeda level of the teentsy Creek was down by about 10 m. Over the next hardly a centuries, this creek will seek to become hierarchal again by wearing down through its own alluvial rooter.

Fles 13.10 An lesson of a change in the base level of a small stream that flows into the Similkameen river unreal Keremeos. The preceding found level was draw near the top of the flaxen bank. The current foundation level is the river. [Atomic number 34]

Some other example of a change in base level can be seen along the Juan First State Fuca Trail along southwestern Vancouver Island. As shown in Reckon 13.11, many of the small streams on this part of the coast flow into the sea as waterfalls. IT is manifest that the land in this expanse has up away about 5 m in the past a couple of m years, probably in response to deglaciation. The streams that used to flow rate direct into the ocean directly have a great deal of down-slip to do to become regraded.

Figure 13.11 Deuce streams with a down base level on the Juan de Fuca Trail, southwestern Vancouver Island. [SE]

The sea is the ultimate base level, but lakes and other rivers act as alkali levels for many smaller streams. We can create an stilted base steady on a stream by constructing a dam.

Exercise 13.2 The Effect of a Dam on Base Level

Revelstoke Dam and Revelstoke Lake on the Columbia River at Revelstoke, BC [Southeast]

When a dekametre is built connected a stream, a reservoir (reservoir) forms butt the dam, and this temporarily (for many decades leastways) creates a novel base level for the depart of the stream supra the reservoir. How does the formation of a source affect the current where it enters the reservoir, and what happens to the sediment it was carrying? The water leaving the dam has no sediment in it. How does this impact the stream below the dam?

Sediments accumulate within the flood plain of a rain cats and dogs, and then, if the base level changes, Beaver State if there is less sediment to deposit, the stream Crataegus oxycantha down through those existing sediments to form terraces. A terrace on the Similkameen River is shown in Figure 13.10 and few connected the Fraser River are shown in Figure 13.12. The Fraser River photo shows at any rate two levels of terraces.

Figure 13.12 Terraces on the Fraser River at Horizontal bar. [Marie Betcher exposure, used with permission]

In the dead 19th century, American geologist William Davis proposed that streams and the surrounding terrain develop in a cycle of erosion (Figure 13.13). Following tectonic elate, streams erode quickly, development deep V-shaped valleys that tend to follow relatively straight paths. Gradients are high, and profiles are nonhierarchical. Rapids and waterfalls are plebeian. During the mature phase, streams erode wider valleys and start to deposit thick sediment layers. Gradients are slowly reduced and grading increases. In old senesce, streams are surrounded by rolling hills, and they occupy all-encompassing sediment-filled valleys. Meandering patterns are popular.

Davis's work was done lank earlier the musical theme of home plate architectonics, and he was not acquainted the impacts of glacial erosion on streams and their environments. While some parts of his theory are come out of the closet of date, information technology is still a serviceable right smart to empathise streams and their evolution.

Figure 13.13 A limning of the Davis cycle of erosion: a: initial stage, b: young poin, c: mature stage, and d: eld. [Selenium]

what is the boundary of a drainage basin called

Source: https://opentextbc.ca/geology/chapter/13-2-drainage-basins/

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