Having re-sequenced my video and extended the transition time on each image, it reached around 10 minutes in length including the end-titles/information. I adjusted the placement of the voice-over segments so that they associated with the images (process described here). Following this there was a lot more space in the sound track and it felt like more was needed. This was confirmed during feedback from a professional film-maker (see SYP blog post).
Although some relevant sounds were available on from the BBC sound effects archive (http://bbcsfx.acropolis.org.uk), I searched for other sources and discovered a site that collected and shared traditional music from the canal (http://www.waterwaysongs.info/index.html). It was here that I found a 1969 recording ‘Narrow Boats’, released on an LP and digitised on the site. This included some fascinating oral histories from the canal, from which I sampled for my soundtrack (appropriate credit added to the video).
I worked at the mixing of the soundtrack to give an improved stereo effect that also helps with a sense of movement in the film. This was achieved envisaging the movement through and across images and recreating that in the soundscape. For example movement across, or from centre and then off by panning the sound across the stereo field; or a sense of distance/depth through volume fade-in/out. There was also considerable effort in balancing the volume levels across the various tracks now in my Garageband file (20 at current count). Throughout this process, I was reminded of what the Beatles managed to achieve with their mere 4 tracks for earlier recordings!
The sound track can be heard in the latest edit of the video.