For keeping good detail at both ends, over 5 stops is a stretch with Velvia 50. The film is designed for high contrast, high saturation. Things fall off quickly once off the middle. Not dramatically but much quicker than for b&w or colour neg.
Good for landscape and nature photography: one wants to enhance all those greens and separate different tonalities. Velvia does that real good. It's bad for portraits of course, where one wants smooth tone transitions and low saturation so folks don't look prematurely aged.
In general I aim for 4-4.5 stops max between high and low light when using Velvia. With Provia and Astia for example, I go up to 6 stops. And with colour neg like Ektar100 or Fuji 100, I go for 7. More with b&w, where I can control the development. All to do with how much tonal compression one can manage to control.
Of course if I don't want to keep detail in a particular area, it's OK to drop it out completely - either end. Hence why I let the underside of the pontoon near the water drop out: not the main point of interest, anyways. In fact: it being so dark kinda contrasts nicely with the white of the boat, so that worked out OK.
Fill-flash can and could be used of course. But I didn't have one with me and it was a bit too far anyway. Besides, unwanted reflections might have been a problem. This being film I can't check for reflections and re-take the shot so I prefer to err on the side of not using flash. Most of the time nowadays I bounce flash off a wall or the ceiling anyways, to prevent the problem.