Surface Water. Streams and Rivers. Stream Erosion and Deposition. River Valleys. Flood Plains and Floods. Tigris – Euphrates River. The Nile River. Yangtze River. Ganges River. Amazon River. The Mississippi River. Water Phase Changes. Hydrologic Cycle. Streams and Rivers.
Streams and Rivers
Stream Erosion and Deposition
Flood Plains and Floods
A river system consists of a river and all of its tributaries.
The drainage basin of a river system is all the land that is drained by the river and its tributaries. A river’s velocity, gradient, discharge, and channel shape affect how it erodes and transports materials.
There are different types of river channel patterns and river drainage patterns.
Dendritic networkA drainage network whose interconnecting streams resemble the pattern of branches connecting to a deciduous tree
A drainage network in which the streams flow outward from a cone-shaped mountain, and define a pattern resembling spokes on a wheel.
Rectangular networkA drainage network in which the streams join each other at right angles because of a rectangular grid of fractures that breaks up the ground and localizes channels.
Trellis networkA drainage system that develops across a landscape of parallel valleys and ridges so that major tributaries flow down the valleys and join a trunk stream that cuts through the ridge; the resulting map pattern resembles a garden trellis.
Silt and clay
Bed load: sand, gravel,
pebbles and boulders
Materials carried in solution cannot be seen.
Rivers wear down Earth’s surface and erode and deposit materials. A river may carry materials in solution, in suspension, and in its bed load.
Over time, sediments build up, forming a delta.
Velocity and discharge affect how much material a river can transport. When river velocity greatly decreases, sediment drops out of the water to form a delta or alluvial fan.
A river drops some of its load when either its volume or its speed decreases eg when it enters an arid (dry) region, crosses an area of porous rock (eg limestone), enters a flat or gently sloping plain or enters a lake or the sea.Material transported or deposited by a river is called alluvium.
Youthful rivers form steep-sided canyons and V-shaped valleys. The lowest level to which a river can erode its bed is called its base level.
Rapids can form as a river runs down a deep slope, while a river that plunges over a cliff forms a waterfall.
A river that has cut down close to its base level tends to erode the sides of its valley, forming a meandering river in a wide flood plain.
River floods are natural events that can have constructive as well as destructive effects.
People have developed different methods to control and prevent river flooding.
1993 Before and After