Photo of Bluebell Woods in Sussex Photo of Bluebell Woods in Sussex

Lees and Leaves

My thanks to Dave Curtis for sending in the above photo and allowing me to share our discussion of it.

Dear Tristan

Whilst out walking with my son yesterday near Basingstoke North Hants, I noticed how the leaves on this road where almost entirely on the right hand side to the direction we were walking.

I am very familiar with our local area so know that the SW winds should be from the right. It appears the wind has come up and over the right hand bank ,scouring the left bank and depositing the leaves in the lee of the right hand bank.

Together with the way the trees are leaning towards the left I wonder if this could be a useful Autumn Winter sign. Thanks for your time,

Dave Curtis

Hi Dave,

Thanks for getting in touch, great pic!

It is sometimes hard to know if there is a human hand involved, but if this is an entirely natural effect then I think you are right and this is a lee effect.

It may be a combination of a lee effect and an eddy. Downwind of any obstruction, like the bank on the right, wind will spin into an eddy and this creates small areas where the wind is heading in the opposite direction to the main flow. If true then some leaves will be dropping onto the right side as they drop out of the main wind current into the calm of the lee, but even the ones that make it a little further may be carried back there by a wind eddy.

This might help explain the massive difference we see in this picture. This is all assuming you haven’t got council trucks firing them all out to one side in your part of the world!

Thanks and all the best,

Tristan

UPDATE:

Hi Tristan

Thanks for getting back to me. There’s definitely no council trucks involved, in fact there’s very little traffic at all down that road.

Dave

Tags