Agenda - Council - 05/25/1999 - Laserfiche WebLink

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hic -iver Processes of Stream Erosion and Deposition 169 :f begins, the flow of water continues to ¢mpinge upon the outside of the bend, developing a meander loop. At the same time, deposition occurs on the inside of the bend as a result of the lower stream velocities in that ~rea. Figure 11.24 Flood-plain teatures seen from an altitude of approximately 6000 m. Note meanders, cutoffs, oxbow lakes, and old meander scars (see also p/ate 14). (C) The meander is enlarged and migrates laterally with contemporaneous growth of the point bar. There is a general downslope migralion of the meanders as they grow larger and ultimately cut themselves off to form an oxbow la.~ Figure 11.23 Development of meander bends and bbrs. The process of meandering involves erosion on the ~utside ora curve in the stream channel, where velocity is O~eatesl, and deposition on the inside of the curve, where ve'rocityJ, s_~ a ~inimum. levees grow higher with each flood, they soon build up high embankments and the river actually can build its channel higher than the surrounding area (figure I 1.25). Backs.'amps. As a result ofthe growth and develop- meat of natural levees, a considerable part of the flood plain is below the level of the river. This area, known as the backswamp, is poorly drained and commonly is the site of marshes and swamps. Tributary streams are un- able to flow up the slope of the natural levees, so they are forced either to empty into lhe backswamp or to Flow Figure 11.25 Natural levees are wedge-shaped depostts ot silt that taper away lrom the stream banks toward the backswamp. They form during flood stages because, as the water overflows its banks, the ve~c, city ~s reduced, causing the silt lo be deposited. As the levees grow higher, the stream channel also rises, sO the r~ver can be h~gner Ihan the surrounding area. parallel to the main stream for many kilometers before connecting with Ihe main stream. Strangely enough, then, the highest surface on the flood plain may be along the natural levees immediately adjacent to the river. lcd_ .he side " ~llt, es . ide ~ (A) Patterns ol stream flow are deflected by any irregularity and move to the opposite bank, where erosion begins. "~' ' +'. . ' ''~ 'the %-~..;