Floods Flashcards
What is the main natural cause of floods?
When there is heavy rainfall over a few days or in a flash flood, the natural watercourses cannot carry all the water away. The level of water in rivers or dams rises. When the level of this wayer rises above the riverbanks or dam walls, it starts overflowing onto the land next to the rivers and dams. The water then submerges these areas
How do human activities cause floods?
Human activities have changed the natural environment by, for example, building cities and dams, and clearing forests to get land for agriculture. This means that the natural environment can no longer cope with heavy rains, which results in floods
List some environmental causes of floods.
Farming
Settlements
Fires
Loss of vegetation
Changing the flow of rivers
How does farming cause floods?
Overgrazing: when too many animals graze on a piece of land, the vegetation is destroyed. Rain then washes the soil into rivers, which silt up and overflow
Over-cultivation: when land has been used for farming for a long time, the soul be CV omes infertile and very little vegetation can grow on it. So, the soil is not protected. It is then easy for the rain the wash the soil into rivers, which silt up and overflow
How do settlements cause floods?
When people build houses and roads, they cover the soil with materials that cannot absorb rainfall. This results in a lot of runoff. If there is too muvh runoff, or if the stormwater drains are inadequate or blocked, flooding will happen
How do fires cause floods?
Some farmers burn the vegetation on their lands to clear it for planting crops. There are also often veld fires in the bush or in the mountains. These fires destroy vegetation. So, the soil is unprotected and the rain can easily wash it into rivers, which silt up and overflow
How can loss of vegetation cause floods?
When land or forests are cleared to build homes or factories, rainfall can no longer be absorbed. So, there is runoff or the water collects on the surfaces, which can cause flooding
How can changing the flow of rivers cause floods?
Farms and people need a constant supply of water. So, many dams have been built across rivers. This has changed the natural flow of these rivers. When there is heavy rainfall, these dams can overflow and cause flooding
What disasters can cause floods?
Tsunamis
Cyclones
Hurricanes
Earthquakes
What effects do floods have on people?
Injury and death
Diseases
Displacement
How do floods cause diseases?
Floods damage water supplies and sewage systems. People then do not have clean water to drink and are forced to drink the contaminated water and eat contaminated food
How do floods cause displacement?
Floods may destroy people’s homes as well as their businesses. These people then have to look for other places to live and work
What effects can floods have on the land?
. When heavy rain falls, especially on land that has poor vegetation cover, it can flow away along indentations/trails on the surface. As the water flows along these indentations, it creates rivulets that can turn into gullies
. Floods can destroy crops. When too much rain falls, the soil becomes waterlogged and the roots begin to rot. The crops then die
. Floods can wash the topsoil away from one area, either into rivers or dams, or deposit it in other areas. This can have devastating effects on agricultural production amd food security in an area
What effects do floods have on buildings and infrastructure?
Floodwater moves with great force and can wash away buildings. When this happens floods can cause chaos, hunger and suffering. In addition, people can be left homeless, hospitals may be destroyed, schooling may be disrupted and transport may become bery difficult because of roads, bridges and railway lines that have been washed away
What is a catchment area?
A natural area from which rainfall flows into rivers and lakes. Some rural communities build their homes on or near catchment areas. When it rains heavily, these areas are quickly flooded
