Rivers

Rivers change the landscape over time.

Water flows down steep slopes near the rivers source, causing vertical erosion.

The slope gradually becomes flat land as the river approaches the mouth.

• Erosion is the wearing away of rock and soil along the river bed and banks.
• Hydraulic Action is when the river forces air into cracks and crevices, gradually wearing the river bank away.
• Abrasion is where rocks get carried along by the river, wearing down its beds and banks.
• Attrition is when rocks, carried by the river, smash together and break into smaller, smoother particles.
• Solution is when particles of rock dissolve into the water.

Rivers Transport material by solution,suspension, traction and saltation.

• Solution is when dissolved materials get transported.
• Saltation is when small pebbles and stones bouce along the river bed.
• Suspension is when small fine material is carried along.
• Traction is when large boulders and rocks roll along the river bed.

• Rivers have an upper, middle and lower course.
• In the upper course, the river erodes the landscape and bends to avoid hard rock, creating interlocking spurs.
• Rapids and waterfalls can form when it runs over alternating layers of hard and soft rock. This is because soft rock erodes more easily than hard rock.
• In the middle course the river flows on a gentler slope with more energy and volume. Sideways erosion widens the channel to the right and then the left forming horseshoe-like loops called meanders.
• Over time the meander becomes tighter. Eventually the river can flow over two ends leaving an oxbow lake.
• In the lower course, a high volume of water flows over flat land. It now has a wide floodplain which is the area around a river that is covered when it floods. Floodplains are fertile and good for agriculture because of the richalluvium in floodwaters.

• A flood occurs when a river is swollen by heavy rain. It bursts its banks and the water spills onto the flood plain.
• Factors in the landscape can make flooding more likely. A steep-sided channel can cause fast surface run-off where the soil cannot absorb the water and so water runs over it. Rivers can flood if there are no trees and plants to catch and drink the water.
• Floods can be catastrophic in the short term but they can have good long term effects too such as boosting soil fertility.
• Floods tend to affect LEDCs more than MEDCs, partly because they depend on agriculture and need the fertile floodplains.
• Hard engineering options usually cost more and have a greater impact on the river and landscape.
• Soft engineering options are cheaper and have less impact on the environment.
• Managed flooding is allowing one area to flood to prevent flooding towns or villages.
• Governments and developers often prefer hard engineering options, while environmental groups prefer softer options, like planting trees. Flood management options need to be sustainable.