Sinuosity

Our final river activity can actually be done without leaving home – you just need a map of your river, either on paper or on your computer.

Sinuosity is a measure of how much the river twists and turns. 

It is very easy to work out – you simply measure from A to B along the river channel (the dashed line) and then from A to B directly across (the solid line).

Sinuosity = river channel distance ÷ direct distance

The direct distance is easy to measure but how do you measure the distance along a twisting line?

One way is to use a piece of string or a shoelace and lay it along the twisty path.  Then take hold of it at A and B and straighten it out…

…so that you can measure the length against a ruler.

Another way is to use the edge of a piece of paper. 

Line the paper up with the first section of the dashed line and make a mark at A and another where the dashes start to move away from the edge of the paper.

With the pen on this point, swivel the paper round a little to line up the next section and repeat all the way along to B. 

If you get to the end of your strip of paper go around the corner!

You can then measure the edge(s) of the paper to find out how far from A to B along the dashed line.

It doesn’t matter whether you measure in centimetres, millimetres, even inches, as long as you use the same units for both the twisty and the direct measurement. 

Sinuosity = river channel distance ÷ direct distance

The larger the number for sinuosity, the more twisty the river. 

As you are working from a map you are not restricted to your fieldwork sites.  Try comparing somewhere near the source, somewhere near the mouth and somewhere in between.  How does the sinuosity change along the river?