Intermittent river facts for kids
Intermittent rivers are also called temporary or seasonal streams. These rivers do not flow all the time. They might dry up completely for part of the year. This happens every year or at least twice every five years.
These rivers are common in dry places. They are found in arid (very dry) and semi-arid (partly dry) regions. These areas cover about one-third of Earth's land.
More rivers are becoming temporary. This is because people need more water. For example, water is used a lot for irrigation (watering crops). Even when dry, these rivers shape the land. They can move a lot of soil and rocks during floods. This causes erosion and builds up new land.
Intermittent rivers are important homes for plants and animals. But human activities often change them. When they are dry, things like pollution can build up. This pollution can then spread when the water returns. Protecting these rivers is important for nature and for people.
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What is an Intermittent River?
In the United States, the U.S. Environmental Protection Agency (EPA) defines an intermittent river or stream as one that flows only during certain times of the year. During the dry season, there might be no water flowing on the surface.
Intermittent vs. Ephemeral Streams
It's helpful to know the difference between intermittent and ephemeral streams. Intermittent rivers have clear riverbeds. They get water from groundwater or other sources. Sometimes, they also get extra water from storms.
Ephemeral streams are different. They might not have a clear riverbed. They mostly get water only from rainstorms. Their beds are usually above the water table. This means they don't have the same features as a regular or intermittent river.
Why Do Rivers Become Intermittent?
Intermittent streams have water when the groundwater level is high enough. This allows water to flow on the surface. The reasons they dry up depend on the climate and location.
For example, streams fed by melting snow or glaciers stop flowing when it gets too cold and they freeze. Or, they might dry up if there isn't enough snow or ice melting. In very dry areas, rivers stop flowing when the water stored underground runs out.
Human activities also cause rivers to become intermittent. People build dams and aqueducts to move water. This water is used for farming, cities, and controlling floods. This has made many rivers that used to flow all the time now dry up.
Big rivers like the Nile and Colorado River have changed. They now dry up in parts because people use so much of their water. This is especially true in dry regions. Climate change, with warmer temperatures, is also making rivers dry up faster.
Where Are Intermittent Rivers Found?
You can find intermittent rivers on every continent. They might even be more common than rivers that flow all the time. Experts believe that over 30% of all rivers on Earth are intermittent.
Some smaller streams are hard to track. If we include them, the number could be over 50%. This number is growing. Many rivers that used to flow constantly are now drying up. This is due to climate change and people taking too much water.
Different Types of Intermittent Rivers
Intermittent streams come in different forms, depending on where they are.
Arroyos: Desert Rivers
Arroyos are a type of intermittent stream found in dry areas. These are common in the American Southwest. They can carve deep channels into the ground. This happens when heavy rains cause strong floods.
Some arroyos became deeper due to human activities. This includes changing how water drains and too much overgrazing by animals. This happened when more people settled in the area long ago.
Glacial Streams: Rivers from Ice
Glacial streams are also intermittent. They get their water from melting glaciers. Their flow changes with the sun's energy. They flow most during the summer when the ice melts a lot.
These streams often dry up or freeze from autumn to early spring. Even during the day, their water flow can change. It depends on how much the sun warms the glacier.
Bournes and Winterbournes
Life in Intermittent Rivers
The plants and animals living in intermittent rivers change as the water level changes. When the river flows, different creatures live there than when it's dry. This means the types of living things can be very different throughout the year.
When the water flows, there are many creatures that like moving water. When it dries up, other animals and plants that like still water or land can thrive. So, these rivers support a wide variety of life. The areas along the riverbanks are also important. They provide homes and food for many organisms.
When Water Returns: The Wetting Front
The dry period of an intermittent stream ends when water returns. This is called "rewetting." It means water starts flowing through the stream again. This happens when more water enters the stream than soaks into the ground.
When the water comes back, it changes things. New nutrients dissolve in the water. Also, different kinds of plants and animals start to live there again.
Land Animals and Dry Riverbeds
When intermittent rivers dry up, land animals can reach new areas. They can find food and resources that were once under water. Sometimes, fish or other water creatures get stuck as the water disappears. These become food for birds, mammals, and reptiles.
Fish That Live in Intermittent Rivers
Many types of fish live in intermittent rivers. The Brassy minnow is one example. It lives in the Niobrara River in Wyoming. Redband trout are found in desert streams in Idaho. The West Fork Smith River in Oregon is home to Coho salmon that return to lay their eggs.
Some fish, like the Cobitis shikokuensis, hide in the wet soil under the riverbed when water is low. When the water returns, they come out. Other fish, like the Highland stoneroller, move to deeper pools to survive when the river starts to dry.
The Food Web in Intermittent Rivers
The food web in intermittent rivers changes a lot. The number and types of living things are different when the river flows, when it shrinks, and when it's dry. These rivers often have a food web that relies on detritus. Detritus is dead plant and animal matter.
The size of the intermittent stream affects its food web. It also changes how many predators there are compared to their prey.
Protecting Intermittent Rivers
Intermittent rivers face many dangers. When people take large amounts of water from these rivers, it can harm the environment. This water is used for factories or big farms. Such actions can change the natural balance of these river habitats.
Human activities can cause problems for these streams. Some problems are short-term, like a sudden spill. Others are long-term, like ongoing pollution. Protecting these unique rivers is very important.
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