River character i stics

What happens to a river as it goes from source to mouth?

It gets• Wider• Deeper • Faster• Stones gets smaller and

rounder

Wider and Deeper 1? • Because more water is added by tributaries,

draining more and more land

Wider and Deeper 2? • Because the greater amount of water erodes the

channel, making it bigger

• Deeper = Vertical erosion • Wider = Horizontal erosion

• Types of erosion?– Corrasion– Hydraulic action

Stone size• Stones get smaller – Why?

– Rolled and bumped and scraped and chipped due to traction

– The resulting erosion on the stones is called…….ATTRITION

Stone roundness• Stones get rounder– Why?

– Rolled and bumped and scraped and chipped due to traction

– The resulting erosion on the stones is called…….

ATTRITION

Stone roundness

The speed of a river is determined by • the gradient of the slope making the water go

faster, • and the friction trying to slow the water down.

River Velocity

SHAPESome shapes have less friction than others. • What is the ideal shape to minimise friction?

BED ROUGHNESS River speed is affected by obstacles in the river.

This increases friction by making the length of the ‘wetted perimeter’ longer.

More bed and bank= more friction

SIZE• The water in contact with the bed and bank is

most affected by friction. • The slowing effect reduces the further away

from the bed/ banks you get. • That means in a larger river, proportionally

less water is touching the bed and banks so it can flow faster.

SamplingSystematic sampling• Systematic sampling is used when the study area includes an

environmental gradient. • With an environmental gradient you would expect a variable to

change in a regular manner as you move away from the start of your survey e.g. the depth of the river as you move further away from the source.

• You could sample along a line (e.g. at 10 equally spaced points on 3km of a river's course to investigate downstream changes in a river). Sample points should be evenly spaced or distributed.

• The number of samples that you take (the sampling size) is important and the area that you complete your sample in.

Finding more data

Source of data Type Ways you can manipulate the data

Data collected by students in previous years Numbers Use this data to build up a picture of the river over a longer course.

Newspaper articles, websites, forums and blogs Written Build up a picture of the location, background and management, find opinions

Maps WrittenMeasure the length of a river course, find the location and height of sites, look for additional factors that might affect the river

Photographs Visual Annotate photographs to illustrate the points you are making

Additional data can be useful to support your field investigation. This is called SECONDARY DATA. It can be derived from

• earlier researchers (e.g. datasets of students from previous years held at Field Centres)• web sources (e.g. census, National Statistics, government bodies, university sources)• written evidence (newspaper articles, blogs, academic papers)• photographs and video

There is no point in just copying out chunks of data. Instead you must show evidence that you have manipulated the data in some way. Here are some examples