Yesterday and today I have been walking the rest of the klong that runs north-south on the western edge of the new Bangkok airport, Suvarnabhumi. (No, I'm not going to say how it's pronounced.) This is a wide canal and once past the southern edge of the airport there are footpaths on both sides most of the way to the Bangna-Trat Highway. On the other side of this road there are no footpaths in sight. I might have to try further south sometime.
This canal isn't very interesting but it did give me a chance to get in some decent exercise. All up over three days walking, always returning to the car, I did about 26 kilometres with the longest day being 12 kilometres. At first I thought the canal might have been part of the airport development but it seems to be a bit older than that. The communities along the canal seem to be mainly buddhist unlike the canals a few kilometres to the north which have a large Moslem population.
Below is a picture from Google Earth which shows the paths with yellow dots. I'm not sure why Google has such a poor resolution view of the airport. Maybe it's a security problem.