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How does the cross section profile of the River Lyn compare with the Bradshaw model?

According to the Bradshaw model patterns of erosion and deposition will cause the cross profile of the channel of the River Lyn to be narrow and V shaped in its upper course closer to the source but increasingly deeper and wider in their middle and lower reaches as it moves closer towards the sea and its mouth (refer back to the model diagram). 

 


Consolidate your thinking

To test the accuracy of the model a number of cross – sections of the river channel and its valley can be constructed from the Ordnance Survey map extract using the same technique as for constructing its long profile.  However, rather than recording the height of each contour crossed at regular intervals the position and height of each contour crossed should be marked on the edge of the piece of paper.  In some places this will present a real challenge particularly when descending or ascending very steep slopes causing the contour lines to coalesce.  It may not therefore be easy in such cases to distinguish one contour line from another.  If this occurs then the priority is to ensure that you record accurately the height of the contour line at the top and bottom of such very steep slopes. 

Cross sections should be drawn at the following points:

Upper course between spot height 359 m at Grid Reference 744453 and Shilstone Hill, spot height 405 m at Grid Reference 759459;

Middle course between Lower East Lyn village 270m at Grid Reference 735483 and the church with a tower 260 m at Grid Reference 750477;

Lower course between North Town Farm spot height 269 m at Grid Reference 725483 to Sillery Sands 0 m (Sea Level) at Grid Reference 738498.

Once you have completed the three cross sections you will need a copy of the three graph templates in Resource 2.4.  In each case the horizontal axis of the graph template shows the horizontal distance along the cross section of the upper, middle and lower course of the River Lyn which you have measured on the edge of your piece of paper. The vertical axis shows height in meters.    To construct the cross section simple lay the edge of the piece of paper along the horizontal axis.  At each point where you have measured the height of a contour simply place a small cross above it at the correct height.  Then join up all of the crosses in a single continuous line.  You now have a cross section of the channel and valley of the upper, middle and lower course of the River Lyn.For support and guidance if required here for either the data collection or construction of cross sections go to

http://www.jaconline.com.au/downloads/sose/2004-09-x-section.pdf

or

http://www.sfu.ca/~hickin/Maps/Chapter%205.pdf


Now go to Investigation 6 -  How do changes in the wetted perimeter of the River lyn Compare to the Bradshaw Model