Rivers are always trying to find a balance between their gradient, base level, and discharge. It is this dynamic that ke

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Rivers Are Always Trying To Find A Balance Between Their Gradient Base Level And Discharge It Is This Dynamic That Ke 1 (81.36 KiB) Viewed 73 times

Rivers are always trying to find a balance between their gradient, base level, and discharge. It is this dynamic that keeps channels changing over time. • Rivers have a gradient, the rate of elevation change per unit length (Figure A1.a). They all end at lower elevations than they begin. • This is best illustrated by a longitudinal profile, a graph of elevation versus river length or distance downstream. • Base level is the elevation below which a river cannot erode its valley (Figure A1.b). Ultimately, sea level is the level below which no river erosion process can lower the land surface. However, not all landscapes grade to sea level, such that a local base level may control the lowest elevation of rivers. Lakes and dam reservoirs are great examples of local base levels. Head Waterfall Steeper gradient Longitudinal stream profile Elevation Ocean, base level Short cascade Gentler gradient Mouth River length (a) River long profile
Artificial local base level Reservoir Dam Sediment accumulation in response Ocean Ultimate base level Sea level (b) Base level Figure A1: River long profile (a) and base level (b). Channelized water above base level represents potential energy. This potential energy is converted to kinetic energy as it flows downstream and helps determine a river's ability to erode. River discharge is the volume of water that moves through a given point in a channel per unit time. It is equal to the product of channel width and depth measured at a given cross-sectional area. This area times the water velocity equals discharge (Figure A2).
(Figure A2). Width Depth Velocity Area = Depth x Width Discharge = Area x Velocity = Figure A2: Calculation of stream discharge
► View Available Hint(s) Reset Help local base level Slope is rise over run in mathematics terms; the comparable term when applied to rivers is discharge longitudinal profile A river's depicts the changes in elevation as a function of distance. ultimate base level is a particular place in the landscape, which can be significantly above sea level, gradient below which rivers cannot erode. is the threshold elevation for river erosion globally. The amount of water moving through a channel at a particular place over a particular amount of time is called