I've spent ages with these river sections half-complete, trying to find an acceptable colour for the water.
Looking online one can find a variety of approaches to represent rivers on the Wargames table and all have their problems. The 'gold standard', I suppose, is sculpted terrain boards with rivers cut into the surface below 'ground level', the river bed realistically modelled (and coloured) then filled with clear or translucent resin, relying mainly on reflection to give a realistic water effect. As well as the usual terrain board problems of storage and lack of flexibility, this has the additional issues of dealing with resin and getting the levels to match.
The alternative is having something to lay on top of the table - with the first obvious problem that rivers are not usually elevated above the surrounding countryside!
The next issue is colour - with no depth of resin, you have to make a conscious choice of colour for the water. Every child knows that water is blue - except, of course, it isn't and the apparent colour depends on the viewing angle, what is being reflected, water depth and anything suspended in the water so it can be a medium blue, pale blue or grey from reflections of the sky; milky white from glacial sediment; dark green from reflected trees; pea green from algae or dark brown/green/grey from a clear view of the river bed. One thing real rivers don't look like is off-white with a light fitting in the middle so a perfectly reflective surface that just mirrors my dining room ceiling won't do.
In the end, and after a number of false starts, I went with the child's image of a blue river and mixed up a medium greenish blue from cheap craft paints. I wanted to fade this into my base earth colour at the edges and, after trying to do this by brushing and blending, gave up and used my air brush - in fact the household emulsion and cheap craft paints seemed to airbrush more reliably than the model paints I normally use!
To try to hide the fact that the river is sitting above table level, I made the banks quite wide with a shallow angle leading up to the river banks. I built up the level with foamboard that I cut to give a fairly steep river bank and gentle lead-in angle, smoothed it off with repair plaster then finished with my usual figure and scenery basing process.
At some point I'll have a go at a more Normandy-specific river - something narrow, shallow and with heavily vegetated banks. Maybe even take a 1km section of a real river and try to duplicate that but for now these will do.