13.1 Streams and Rivers13.1 Streams and Rivers

Key Idea:Key Idea:Streams and rivers carry a portion of Streams and rivers carry a portion of

the precipitation that falls on land back the precipitation that falls on land back to the oceans.to the oceans.

Lesson ObjectivesLesson Objectives

1.1. Define a river systemDefine a river system

2.2. Describe the characteristics of a stream or Describe the characteristics of a stream or river that affects its ability to erode river that affects its ability to erode sediments.sediments.

River SystemsRiver Systems

A permanent body of running water is called a A permanent body of running water is called a streamstream or a or a river.river. Rivers carry more water Rivers carry more water than streams. than streams.

A small stream may run into a larger stream; A small stream may run into a larger stream; the larger stream may run into a river, and the larger stream may run into a river, and so on. A small body of water which runs into so on. A small body of water which runs into a larger one is called a a larger one is called a tributary.tributary.

A river systemA river system

La Plata River System_ South La Plata River System_ South AmericaAmerica

River SystemsRiver Systems

Usually a large river collects all the smaller Usually a large river collects all the smaller rivers in a geographical area. This large rivers in a geographical area. This large river and all its tributary form a river and all its tributary form a river river systemsystem..

The surface covered by a river system is The surface covered by a river system is called a called a drainage basindrainage basin or or watershed.watershed.

The high land that separates one river The high land that separates one river system from another is called system from another is called divide.divide.

Drainage Basin or WatershedDrainage Basin or Watershed

Mississippi Watershed is the largest Mississippi Watershed is the largest in the USin the US

Characteristics of Streams and Characteristics of Streams and RiversRivers

The ability of a stream or river to erode and The ability of a stream or river to erode and transport sediments is affected by many transport sediments is affected by many factors. The most important factors are:factors. The most important factors are:

VelocityVelocity GradientGradient DischargeDischarge ChannelChannel

VelocityVelocity

The velocity of a stream or river is the amount of The velocity of a stream or river is the amount of space the water travels in a given amount of time. space the water travels in a given amount of time. A fast running river has more kinetic energy, A fast running river has more kinetic energy, therefore it erodes materials more quickly and can therefore it erodes materials more quickly and can transport larger particles than a slow moving river. transport larger particles than a slow moving river. The velocity of a river is determined by: The velocity of a river is determined by:

the steepness of the slopethe steepness of the slope The amount of water traveling downstreamThe amount of water traveling downstream The shape of the path through which the water The shape of the path through which the water

travels.travels.

Velocity, IllustratedVelocity, Illustrated

GradientGradient

The steepness of the slope of a stream or The steepness of the slope of a stream or river is called river is called gradient.gradient. A river’s gradient A river’s gradient varies along its course. varies along its course.

A river flowing up the hill on steep slope, A river flowing up the hill on steep slope, has a high gradient.has a high gradient.

A river flowing on a flat plane, with a very A river flowing on a flat plane, with a very small incline, has a very low gradient. small incline, has a very low gradient.

DischargeDischarge

The discharge of a river is the amount, or volume The discharge of a river is the amount, or volume of water that passes a certain point in a given of water that passes a certain point in a given amount of time. amount of time.

In many rivers the discharge increases In many rivers the discharge increases downstream , because the tributaries continually downstream , because the tributaries continually add more water. In the desert, discharge may add more water. In the desert, discharge may decrease downstream. decrease downstream.

Discharge varies throughout the year: during Discharge varies throughout the year: during increased precipitation, or when the snow is increased precipitation, or when the snow is melting, the discharge increases. The velocity of melting, the discharge increases. The velocity of the river also increases. Rivers become wider, and the river also increases. Rivers become wider, and deeper, and floods are possible. deeper, and floods are possible.

Discharge Increases DownstreamDischarge Increases Downstream

River Channel River Channel

The path through which the water flows in a The path through which the water flows in a stream or river is called its channel. The size and stream or river is called its channel. The size and shape of the channel affect the velocity of the shape of the channel affect the velocity of the water. water.

The channel of a shallow, winding stream with The channel of a shallow, winding stream with many boulders has a great deal of surface area in many boulders has a great deal of surface area in contact with water flowing through it; friction slows contact with water flowing through it; friction slows the water down. the water down.

A straight channel that is wide and deep has les A straight channel that is wide and deep has les surface area in contact with the water, so the surface area in contact with the water, so the water’s velocity is greater.water’s velocity is greater.

Boulders increase friction and Boulders increase friction and decrease the velocity of the riverdecrease the velocity of the river