Rivers

Rivers• Almost half of the water that falls to the

Earth’s surface eventually ends up in a stream or river (runoff), where it travels overland to the oceans. Streams and Rivers are an essential part in the water cycle and account for most of the erosion of Earth’s surface.

Rivers• A tributary is a

stream that runs into a larger stream. The main river will eventually drain into the ocean. A river and all of its tributaries is called a river system.

The drainage basin, or watershed, of a river includes all the land that drains into the river directly or through its tributaries.

• The largest in the U.S.

A watershed is a precipitation

collector!

Rivers of VA

                                                                                                          

Every drop of water (or pollution!) that falls into the watershed goes into that river

The high land that separates one drainage basin from another is called a divide.

Watershed

To the Atlantic

To the Pacific

The major divide in the U.S. is called the Continental Divide.

The beginning of a river is known as the SOURCE.

Freshwater Spring

or

Precipitation

River Delta

When the mouth of a river finally reaches its

destination, be it ocean or lake, the water slows down

& deposits its sediment, forming a delta.

Greek Alphabet

Safid River Delta, Rasht, Iran

See the sediments going into the ocean!

Mississippi River Delta

Sediments from the Mississippi come from everywhere between the Appalachian & Rocky Mtn chains. Eventually they may fill the Gulf of Mexico!

An Alluvial Fan is similar to a delta, but forms on land where a river emerges from a

mountainous area and flows out onto a more gently sloping plain.

Alluvial Fan

Alluvial Fan

Source

River Valley

Tributary

Floodplain Meander

Oxbow Lake

Delta

Parts of a

River System

River Development

Youthful

Mature

Old

The three stages in the development of a river are described as youthful, mature, and old.

Most rivers begin in the highlands or mountains. There water sources such as melting snow and ice feed fast-moving young rivers.

As the young rivers feed into larger rivers over flatter land they may take on characteristics of mature rivers.

As the river approaches the ocean it slows down and becomes wider & flatter taking on the characteristics of an old river.

FROM VALLEY TO FLOODPLAIN 1. A youthful river has a steep slope, fast-moving water, V-shaped valleys, and many rapids and waterfalls • Rapids & Waterfalls - caused by steep slopes and

differential erosion.

FROM VALLEY TO FLOODPLAIN

Flooding speeds up erosion and deposition creating a broader floodplain on the valley floor.

FROM VALLEY TO FLOODPLAIN

2. A mature river has a shallower slope, is slow moving, and winds back and forth in broad curves called meanders.

FROM VALLEY TO FLOODPLAIN

3. An old river moves very slowly, has a nearly flat slope and oxbow lakes. Elevated ridges along stream banks are called natural levees.

River Development

River Meander

3-D View of Meander

River Meander

Meander Formation

Difficult Run DIFFICULT RUN

Inside Curve: deposition

Outside Curve: erosion

North Slope, Yukon

Meander Oxbow LakeA river wants to find the shortest, straightest way

to the ocean, so it will change paths along the floodplain cutting off wide loops leaving behind a curved body of water called an oxbow lake.

Oxbow Lake-To-Be

FLOOD!

Rivers may overflow its banks as a flood. The floodwater may cover

part or the entire valley floor where the river runs eroding and depositing

sediments.

This part of the valley floor is called the floodplain.

Floods can erode or…

.… deposit.

Coarse-Grained Sediments-

Deposited by fast-moving water

Fine-Grained Sediments-

Deposited by slow-moving or standing water

Characteristics of Streams & Rivers • Velocity – the distance water travels in a certain amount

of time; related to the amount of energy the water has; fast moving rivers erode material more quickly and can carry larger particles

• Gradient – the slope or incline of a stream; sources of rivers tend to have large gradient whereas deltas of rivers have small gradients.

• Discharge – the volume of water a river or stream passes in a certain amount of time; becomes larger as tributaries add water; seasonal changes

• Channel – the path through which water flows; size and shape effect velocity

Erie Canal