Rivers and coasts, Year 7: more practice

Evaporation

HintIt happens at the surface of seas, lakes and rivers.

The whyEvaporation is the first step of the water cycle. Warm air carries the vapour upwards.

It condenses into tiny liquid droplets, forming clouds

HintThe vapour changes state again.

The whyCondensation is the opposite of evaporation. When droplets grow large enough they fall as precipitation.

The River Severn

HintIt flows from Wales into England and out to the Bristol Channel.

The whyThe Severn is about 354 km long. The Thames is the longest river wholly in England.

A tributary

HintThe larger river is joined by these.

The whyA river's tributaries gather water from across its drainage basin.

A confluence

HintTwo rivers become one here.

The whyA tributary joins the main river at a confluence. The word means 'flowing together'.

A watershed

HintRain falling either side drains into different rivers.

The whyRain that falls on one side of a watershed flows into one river, and rain on the other side flows into another.

The river drops the material it was carrying

HintIt happens when the flow loses energy.

The whyWhen a river slows down, it can no longer carry its load. Sand, silt and pebbles settle on the bed or banks.

The inside bend

HintThe water flows slower on this side.

The whySlower water has less energy, so it drops its load. Faster water on the outside bend erodes the bank.

Traction

HintThey are rolled, not lifted.

The whyTraction moves big boulders in floods. Saltation hops smaller stones. Suspension and solution carry fine material and dissolved minerals.

They knock against each other and the bed and wear away (attrition)

HintThink of stones bumping into one another all the way down.

The whyThis process is called attrition. It is one reason that river sediment is finer near the mouth.