After heavy rain or snowmelt, rivers burst their banks spilling out in a sheet of water over the surrounding countryside. Repeated thousands of times over the lifetime of a river, this process creates a large, flat flood plain. Mature rivers usually have extensive flood plains especially in the lower reaches. Vast numbers of the world’s population live on flood plains.

During a flood a number of things can happen, often relatively quickly:

• Large amounts of silt and sand are deposited on the flood plain, building over centuries into rich, deep, fertile soils that often completely fill the valley bottom.
• Natural, low banks or levees are created near the channel as the river overspills and then drops the heavier stones and pebbles first.
• Rivers find it much easier to change their course during floods, straightening curves and sometimes cutting off meanders to form ox-bow lakes.

The Importance of Rivers

A river has a dramatic impact on the land through which it flows, being both a powerful force in forming and shaping the land and a vital life-giving resource to everything within its basin.

Not only does it provide water for people, farms, factories and leisure activities, but it also attracts villages, towns, routes for travel and tourism.

Recreation

Rivers and reservoirs are an important recreational resource, with large numbers of people taking part in activities such as fishing, birdwatching, walking, canoeing, sailing and windsurfing.

Meanders

Meanders are a fascinating and important part of all rivers, large or small. They are formed as the river flows across a flat flood plain, slowing down and eroding more sideways than downwards, creating loops and lazy curves. At the same time the river is also depositing the load of silt, sand and stones it has been carrying.

As the river swings round the outside of the bend it is forced to flow faster, cutting into the bank, eroding away material. Meanwhile as it flows round the inside of the bend it is slowed down, dropping its load of silt, sand and stones, depositing material in a mini beach. In a meander therefore the key point is that the river is eroding and depositing material at the same time.

Water and Sewage Treatment

Clear water does not mean clean water. Much of the water that children see every day in the world around them may appear clean but most natural waters need some form of treatment before they can be used. This usually involves: screening to remove any large objects; clarification where a chemical is added to cause particles to clump together; filtration through sand and gravel beds; disinfection often using chlorine. The cleaned water is then stored in totally enclosed concrete service reservoirs before being piped to customers.

Cleaning water before we use it, however, is only half of the treatment process. The waste water or sewage we produce from both domestic and industrial waste also has to be cleaned and treated before it can be safely returned to the river. This usually involves a range of processes including screening, settling tanks and percolating filters.

The River’s End

Newport is a bustling commercial centre and port situated at the mouth of the River Usk. It has a classic, urban industrial landscape in sharp contrast to where the river began its journey. The town, the third largest in Wales, grew up around the docks, where coal and iron-ore from the nearby valleys were shipped all over the world. During the Industrial Revolution, one-third of the world’s coal came from South Wales.

137 kilometres after bubbling out of a spring on the slopes of the Black Mountain (OS Landranger 160 1:50,000, grid reference 818238), the River Usk finally flows out into the sea completing its journey from source to mouth.

(Note: the printed version of the Riverflight Teachers' Guide is available as part of the Riverflight Map Pack from the 4Learning online shop.)