River Erosion

River Erosion

Open Ended

What can river erosion lead to?

​River Systems

If you live in Michigan, chances are pretty high that you’re not far from water. Maybe you live near a small stream that empties into a larger stream. Or perhaps you live near a major body of water like the Grand River or Lake Michigan. Water is an important characteristic of life in Michigan: It provides habitats for birds and fish, helps with transportation, and provides us with water for drinking.

​River Systems

​Rivers are systems.

No river functions independently. Water moves through smaller streams that drain into larger streams and eventually empty into lakes or oceans.

It’s a continuous cycle.

​River Systems

​River systems share several common traits. Rivers always flow from areas of high elevation to areas of low elevation. As rivers and streams move downstream, they widen and move more water. This occurs because tributaries (smaller streams and rivers) join together along the course of a river. As tributaries combine, more water flows in fewer channels.

Open Ended

Why do rivers widen downstream?

​River Systems

​We can measure the velocity of a stream in order to find out how long it takes a particle of water to move a certain distance. Once we know a stream’s velocity, which is measured in meters per second, we can then compute that stream’s discharge. Discharge is a measure of exactly how much water moves past a certain point. To compute discharge we multiply velocity by the area of a cross-section of the stream at a given point. Discharge is expressed as cubic meters per second (m3/s). Naturally, larger rivers have greater discharge than smaller streams.

​River Systems-Erosion

​Another common characteristic of all rivers and streams is that they carry sediment. In fact, did you know that rivers and streams are one of the reasons the oceans are salty? This may seem counterintuitive, because rivers and streams are freshwater, but the ocean is salty because of river erosion. As rivers move downstream, they wear away rocks, which contain ions like potassium, sodium, and magnesium. Rivers eventually deposit these ions into oceans, where they stay. It’s these ions that make the ocean salty.

Multiple Choice

Why are oceans salty?

• As rivers move downstream, they erode rocks which contain salty ions. Rivers eventually deposit these ions into oceans.

• As rivers move downstream they wash over salt factories and take the salt to the oceans

• Because their best friend "forgot" to invite them to the sleepover 

​River Erosion

​In addition to carrying dissolved salts and ions, rivers can carry and deposit other sediment as well. Fastmoving streams with a steep slope (or gradient) can move large boulders. If you’ve ever visited a mountain stream, you may have noticed that there were large boulders in the streambed.

​Over time, these rocks will slowly be moved downstream. At the same time, the water in the stream will slowly break down these rocks. The size of the sediment a river can carry is directly related to its speed. Slower-moving rivers are more likely to have a streambed of silt or sand, instead of gravel or large rocks.

​River Systems

​Rivers have a shape that is ideal for carrying water downstream. Most river and stream banks are broad and flat, and have a deep channel in the middle of the waterway. If too much water is in the channel of the river, the water naturally spills over the bank. High water flow in rivers can happen during spring runoff (when snow in the mountains melts) or during large storms. The area where a river’s water overflows is called the floodplain.

​River Systems

​Historically, rivers offered the best way to travel and trade goods between cities. Today, large numbers of people continue to live by rivers. Since many towns and cities are located along streams and rivers, however, strong floods and storms can endanger both lives and property. Rivers, like so much else that we find in nature, have inherent risks and dangers along with their numerous benefits.

Multiple Choice

Rivers create...

• u-shaped valleys

• v-shaped vallys

• o-shaped valleys

• t-shaped valleys

Multiple Choice

Glaciers create...

• v-shaped valleys

• t-shaped valleys

• ice ages

• u-shaped valleys

​River Erosion Example: The Grand Canyon

​​River Erosion Example: The Grand Canyon