An ungraded stream has an uneven, "bumpy" profile. This can be thought of as an equilibrium condition. A graded stream is one in which a stream profile has a smooth, concave shape. If two streams on opposite sides of a ridge or divide erode toward each other, one stream may end up "capturing" the other. Gullies can erode and extend back toward the headwaters overtime due to the process of headward erosion. As gradients decrease, downward erosion is less dominant, and lateral erosion begins to dominate, forming meanders.ģ. At higher gradients, downward, vertical erosion is more dominant. Material may be moved downstream incrementally, in short spurts along the bottom of the river bed. Material may be suspended in the water due to the continuous turbulent motion of the water. Water may dissolve rock as a part of chemical weathering and carry the material downstream. Rivers move material down stream in one of three ways.ġ. In a meandering river, water will tend to flow fastest along the outside bend of a meander, and slowest on the inside bend.Ī. Toward the middle of a river, water tends to flow fastest toward the margins of the river it tends to flow slowest.Ģ. At different areas in a channel, water flows at different speeds.ġ. Anything that reduces surface area also reduces the amount of friction and causes faster flow. Generally, anything that increases the surface area of the channel, against which the water flows will tend to slow the flow because of the increase in friction. Smoother channels also allow faster flow of water rougher channels slow water flow.ģ. Broader flat channels tend to slow a river down.Ģ. Generally a narrower, more circular river channel allows faster flow of water. Channel shape and roughness affect a river's velocity.ġ. At the lowest gradients, deposition, rather than erosion is dominant. At base level, the gradient is zero, or horizontal.ģ. A river will not erode below the base level. This theoretical limit is called the base level. There is a theoretical limit to how low a river will erode. Gradients are highest nearer the river source and lowest nearest the delta.Ģ. A profile is a cross section along the path of a river, from its source to the river delta.ġ. Gradients can best be seen along the profile of a river. You can think of a gradient in terms of the number of feet a river drops in a mile along its course. Gradient is the downhill slope of a river. What affects the velocity of water in a river?Ī. What's left either seeps into the ground to become ground water or flows over the land's surface as streams that eventually flow to lakes or oceans. More than half the water that falls to the Earth quickly returns to the atmosphere through evaporation.ĭ. The water vapor eventually forms clouds which results in precipitation.Ĭ. Most water enters the atmosphere by evaporating from oceans. The hydrologic cycle (water cycle) describes how water moves at Earth's surface.Ī. Gravity erodes through mass wasting processes. Wind erodes through wind processes (dunes).ĭ. Coastal ocean waters erode through wave processes.Ĭ. Surface water erodes through river and stream processes.ī. Erosion can occur through several means.Ī. Erosion involves the transport of rock and soil material subsequent to and during weathering processes. Rivers and Streams, and erosional processes Rivers and Streams, and erosional processes
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