Flooding can cause damage to homes, businesses, infrastructure and communications.
Hard engineering involves building artificial structures which try to control rivers. They tend to be more expensive. Each hard engineering strategy has its advantages and disadvantages.
The dam traps water, which builds up behind it, forming a reservoir. Water can be released in a controlled way.
Straightening the river speeds up the water so high volumes of water can pass through an area quickly. Dredging makes the river deeper so it can hold more water.
Raising the banks of a river means that it can hold more water.
The floodwater flows into the relief channel and is taken either to an area where it can be absorbed, or re-enters the river further down its course.