The bridge carries the road over a stream which another contributor has identified as the River Arun http://www.geograph.org.uk/photo/3216480 I can't see that that can be the case (this far inland) but it has to be said that the OS offers very little help - you can trace the stream for some miles on the map without its being named. It could perhaps be the River Lox http://www.geograph.org.uk/photo/2851447 or a tributary of the Lox. That would at least mean that it is part of the Arun catchment.
Uploaded to Geograph by Stefan Czapski on 30 October 2013
Photo © Stefan Czapski, 30 October 2013. Licensed for reuse under this Creative Commons licence