There is an “impossible” school of photography, who always want to tell you how complicated or difficult it was to take a particular photograph. While it can be interesting, it is irrelevant, ‘cos photography is about pictures.
The River Thames is tidal for much of its length, which means that at low tide, large stretches of bank are exposed, sometimes showing interesting details. At the time, I lived in Chiswick, so it was quite easy to find a time to wander out on to the river bed. The only snag being, that you had to keep an eye for when the tide turned, ‘cos then you could find yourself wading or possibly even swimming out of it (hard with a camera bag).