Came across this on a visit to a village. A riverbed plantation uses this method to protect tomato saplings from dew.
[size=100]All images taken on 8th Feb 2014 in a north eastern region of Punjab bordering Himachal Pradesh. [/size]
Orientation is crucial for this method to succeed. For obvious reasons you should not block the sun. In this case the plantation was done generally on East-West axis.
But if you look at the Google Maps screenshot of the site below, you can see that more precisely the orientation was slightly tilted and it can be called south-west to north-east plantation.
For general info about riverbed cultivation of vegetables including recommended varieties, see attached word file.
River-bed cultivation of Vegetables-410.doc (120 KB)