During your visit to the River Darent your class should have been able to calculate the relative flow, width and depth at Westminster and about 150metres north of Franks Bridge , depending on time available and weather conditions and river depth. Below is a typical example of data collected which may help you follow up your visit back at school, including how to find the speed in metres per second. It was collected by a Year 6 class in spring 2008 but it could be any month of any year and would depend on rainfall levels during a particular season.

Your class probably observed that generally where the river flows fastest it is deeper with larger pebbles on the bed and where it is slower the river is shallower with smaller stones on the bed.

Westminster Bridge
The straighter part of the river at Westminster Bridge has a fairly consistent depth, though is a little deeper nearer the steps which may be due to the faster flow made possible by the weir on the other side of the bridge. You may also notice from the average speed that the concrete pillar supporting the bridge slows the flow of the water.

Franks Bridge
The gradual bend 150 metres north of Franks Bridge illustrates a deeper part of the river on the far end opposite the path. This was shown with the flow experiments using the sponge balls.

Graphs to compare the typical depths at two different places on the River Darent.
Westminster Bridge		Average River Speed
		Ball Colour Average speed (m/s) Red 0.63 Green 0.48 Blue 0.71
Franks Bridge	Average River Speed
	Ball Colour Average speed (m/s) Red 0.77 Green 0.53 Blue 0.45

You should be able to use the example with the data your class collected.
You will find more data in the ‘Study Topics' part of the Horton Kirby EEC's website.