Capturing the movement of the water is key to really translating the essence of a place to a photograph and is crucial as it plays a huge role in setting the mood of a scene. Shutter-speed control and choice of ND filters are the typical methods of controlling the degree of silkiness vs frozen action of water achieved with faster shutter speeds. Finding the right shutter speed to really make the water look optimal, is of course subjective, but it’s something I have often found frustrating to try and find.
A technique I have enjoy using in these situations is the cameras built in multiple exposure mode. I shoot with a Canon EOS 5Ds which offers different types of multi-exposure control blending, additive, average, bright and dark. With a bit of experimentation shooting 2, 3 or 4 images in bright mode provides some excellent results. As the water on a river tends to surge, often one surge provides nice water movement, but more provides extra texture. These combined shorter exposures are more textured than a longer exposure which I find very often is far too smooth to really convey the right atmosphere. The same could be achieved with a series of images opened as layers in photoshop and blend modes applied to the layers, but personally I enjoy the creative process of capturing these images in camera and it speeds up my post processing workflow too.
I always favour an overcast day for riverside photography, to avoid the bright highlights which tend to restrict the direction of shooting. Often I shoot late into the evening when the low light aids slower shutter speeds without neutral density filters being needed. The warm tones tend to pop even better in the golden hour light too.