【5th Grade Science】The Action of Running Water and Changes to the Land
Hello! Today, let's learn about how the shape of the "ground (land)" we live on is formed.
When river water flows, it actually uses its "amazing power" to erode the ground, carry sand and rocks, and pile them up somewhere else.
Once you understand this power, the view of a river will look completely different! It might feel a little difficult at first, but don't worry—I've narrowed down the key points for you. Let's get started!
1. The "Three Actions" of Running Water
River water has three main types of power. Remembering these three as a set is the biggest key to this unit!
① Erosion
The action of running water wearing down (eroding) the land.
Example: The riverbed or riverbanks being gradually carved away by the force of the water.
② Transportation
The action of carrying the eroded rocks and sand downstream.
Example: Flowing water carrying soil and stones along with it.
③ Deposition
The action of the transported stones and sand settling (piling up) where the flow slows down.
Example: Sand and stones accumulating on the riverbed or banks, creating flat areas.
【Tip!】 How to remember
Try remembering them with the rhythm "E-T-D"!
E: Erosion (wearing down)
T: Transportation (carrying)
D: Deposition (piling up)
2. Reasons Why Water Power Changes
There are mainly two reasons why the power of water gets stronger or weaker.
① Amount of Water (Water Volume)
When the amount of water increases, all three actions—erosion, transportation, and deposition—become stronger.
After a heavy rain, the river turns muddy and brown, possessing enough power to roll even large rocks downstream.
② Speed of the Flow (Flow Velocity)
The faster the speed, the stronger the power to erode and carry the ground.
The steeper the slope, the faster the water flows.
【Did you know?】
Why are river stones "angular and large upstream, but round and small downstream?"
It's because as they are transported, they collide with each other and rub against the riverbed, wearing down their edges. The river is like a "natural file"!
3. The Appearance of Winding Rivers
Where a river curves, the way the water flows has some big characteristics. This is an important part that often appears on tests!
■ Outer Side
・Speed of flow: Fast
・Action: Erosion (wearing down) is active.
・Appearance: The bank is often carved away into a cliff-like shape, and the water is deep.
■ Inner Side
・Speed of flow: Slow
・Action: Deposition (piling up) is active.
・Appearance: Sand and stones accumulate, often forming a river beach, and the water is shallow.
【Common Mistake!】
It’s easy to misunderstand and think "the inside of a curve is faster," but it’s the opposite!
Imagine this: when running a race on a track, the person on the outside has to run very hard to keep up. Water is the same; it flows more vigorously on the outside, which is why it erodes the bank.
4. Landforms Created by Running Water
Over many years, rivers create unique landforms.
● Alluvial Fan
A landform shaped like a folding fan that forms where a river emerges from the mountains onto flat land. Because the steep mountain flow suddenly becomes gentle, the rocks and sand it was carrying are dumped all at once.
● Delta
A low, triangular landform that forms at the mouth of a river where it flows into the sea or a lake. Since the flow almost stops, fine sand and mud settle there.
【Summary: Differences by Location】
・Upstream (near the mountains): The flow is fast, and the stones are large. V-shaped valleys form.
・Downstream (near the sea): The flow is slow, and there is a lot of sand and mud. Wide, flat land spreads out.
5. Heavy Rain and Our Daily Lives (Disaster Prevention)
The power of running water can sometimes cause major disasters.
When it rains continuously, the amount of water in the river increases (rising water), which can carve away banks or overflow the embankments (flooding).
What we can do:
1. Check a hazard map to see if your home or school is in a safe area.
2. Never go near a river when it is raining.
3. Make it a habit to check the "rainfall amount" in the news and weather forecasts.
★ Final Review ★
If we narrow down this lesson to 3 points...
1. The actions of water are the three: Erosion, Transportation, and Deposition!
2. If the amount of water increases or the slope is steep, the power becomes stronger!
3. In a winding river, the outer side is eroded, and the inner side is filled with deposits!
Now you've mastered the basics of "the action of running water"!
If there is a river nearby that you can observe safely, try looking at the difference between the inside and outside, and look at the shapes of the stones. If you can say, "Oh, this part is being eroded," then you are a science master!