Rivers and streams are powerful, ever-changing systems that can alter the surface of the Earth. While they share many similar features, they can be vastly different. In this lesson, we will learn how rivers and streams form, transport sediment, and flood.
What Is a River?
Every Sunday, Jenny looked forward to a big family dinner with her dad's famous mashed potatoes. She always liked to see how big of a mashed potato mountain she could make. Jenny loved pouring a stream of gravy over the top and watching as it flowed down the sides. Sometimes, if she poured slowly, the gravy would carve little paths in the mountain and other times, if she poured too quickly, it would get all over everything on her plate!
'You know,' noticed her grandfather, a scientist, during one dinner, 'your mashed potato mountain reminds me of the rivers and streams I study at work.' Jenny didn't know much about rivers and streams and had no idea how the two could be related. Grandpa went on to explain that a river is a large flowing body of water that flows into an ocean or lake, and a stream is a small river.
Rivers and streams can be found on most areas of the Earth. Some flow all year, while some flow seasonally or even only during years with heavy rainfall. While rivers can have different features, they all have certain things in common.
The beginning of a river or stream is called the source, where water is supplied by rain, other bodies of water, or melting snow and glaciers. Rivers form high up in mountains and start out as slow moving streams. As the water flows down the steep slopes, it begins to move quicker and forms rapids or waterfalls, which are falling water that occurs when rivers flow from a high place to a low place.
The rushing water causes erosion, which occurs when pieces of earth that have been weathered and worn away are moved to another place. Rivers can erode some landforms, like mountains, but also create others.
Rivers and streams can carry sediment, which is pieces of earth that have been broken off by erosion. The sediment is carried downhill, where it forms new landforms through the process of deposition, which happens when earth material that has been eroded is placed, or deposited, in another area.
Fast moving water deposits pebbles and larger stones, while slow moving water deposits smaller particles of sediment. The water and sediment eventually ends up on beaches and in the ocean at the mouth, or end, of the river, where it empties into another body of water, like a lake or ocean.
Rivers Create New Landforms
Through the processes of erosion and deposition, rivers and streams can drastically alter the Earth's surface. The kinds of features and landforms created depend on their slope, speed, and volume. The rushing water of rivers helps to carve new features into the surface of the Earth. One of these features is a channel , or path a river or stream follows. Channels can dry up or change course over time.
Rivers and streams can develop meanders, or s-shaped curves. The water flows fastest at the outside of the curve, where it erodes the sides of the riverbank and provides sediment. The water flows slowest at the inside of the curves, and the sediment is deposited in those areas. Rivers and streams can have just one channel, as is the case with meanders, or many channels. Braided streams are streams with many channels that overlap each other. The channels are continuously changing in a braided stream.
Valleys are another type of feature that can be created by rivers and streams. River valleys are formed when fast moving water cuts across the sides of land, and v-shaped valleys form when rivers cut through mountains. When rivers flow onto flatter land, some of their sediment is deposited, which can create new landforms.
River deltas are triangular shaped landforms that form from sediment deposited when a river flows into a larger body of water. Beaches are a type of landform, along a shoreline, that is usually made of sand or gravel. The type of material that ends up on the beach depends on the rock material that has been eroded from the mountains above. Alluvial fans are fan-shaped areas of sediment that form when water from steep slopes flows onto flat plains below.
Rivers are important sources of food and habitat for wildlife, transportation, power, and recreational fishing and swimming for humans. While rivers and streams are desirable areas for building homes, they pose a natural hazard, as they often flood. Floodplains, or flat land near a river that floods, while very fertile and good for growing crops, is not always suitable for buildings and homes.
When rivers overflow onto the riverbank, the rushing water can cause destruction of homes and buildings and create a hazardous drowning risk. Wildlife habitats can also be destroyed by floodwaters. River flooding can occur from heavy rainfall, or seasonally, due to fast-melting snow. While some rivers flood in regular patterns, most don't, making the prediction of flooding very difficult.
As they finished dinner, Grandpa asked Jenny what she had learned. 'I know that water for rivers and streams starts at the source. The water then flows into a waterfall or rapids and ends at the mouth. Along the way, rivers and streams can erode the Earth's surface, carry sediment, and create new features and landforms. Rivers are important for humans and wildlife, although river flooding can cause damage to their habitats. Oh, I also know that I really love dad's mashed potatoes!'
Completion of this lesson could result in your ability to:
- Differentiate between a river and a stream
- Describe the life of a river from source to mouth
- List different features and shapes of rivers
- Understand that rivers can erode and create land forms, and give examples
- Discuss some of the benefits and risks associated with rivers