How do changes to the wetted perimeter of the River Lyn compare with the Bradshaw model?

Consolidate your thinking – fieldwork to calculate changes in the wetted perimeter of the River Lyn

According to the Bradshaw model the wetted perimeter(the length of a river’s bed and banks in contact with the water) will always increase with distance from source to mouth as more water enters the river system through tributaries and run off as it progresses downstream.  To test this assumption against the real world example of the River Lyn measurements can be taken at sample points along the course of the river.  The film and narration in

The video below shows clearly how to measure the wetted perimeter of a river and further guidance is available at


If at least 8 measurements of the wetted perimeter are made along the upper course of the River Lyn and a minimum of 8 in its middle course and a further 8 in the lower course then the Mann Whitney U test can be used to assess whether the difference between the medians of two sets of data e.g. Upper and Middle; Middle and Lower and Middle and Upper and Lower are significantly different assuming a null hypothesis of no significant difference existing between the locations.The following sites along the river are suggested as possible locations to take the sets of wetted perimeter measurements required:

Assessing risk and identifying control measures to manage risk
Please refer back to guidance on this page  and use the template with regard to fieldwork above.

Secondary data sets

If access to these locations is not possible for primary data collection then the following tables provide sets of secondary data obtained from 11 sites along the length of the river system  for the students to test statistically:

 Site 1Site 2Site 3Site 4Site 5Site 6Site 7Site 8Site 9Site 10Site 11
Distance Downstream (m)100011501375287033603725664071907630839010330
Wetted Perimeter (m)1.661.872.513.052.354.157.284.7816.214.121.3

Now go to Investigation 7  - How do changes to the load size and shape of the River Lyn compare with the Bradshaw model?