Watercolor signed Thinel, landscape, Marais Poitevin

A very pretty watercolor, probably depicting the Marais Poitevin at sunset, with pollarded willows or ash trees in the foreground. I acquired it about 50 km from Niort, hence the location I'm suggesting. It's signed, G. Thinel I believe, but I haven't been able to identify the artist, who is clearly very talented. The lines are fine and precise, demonstrating a lovely mastery of technique. The colors and shadows are also well-handled; the painting is beautifully realistic. This watercolor is in a dark wood frame with a white-painted border and is under glass. The original kraft tape on the back was peeling off considerably, so I replaced it. I was curious to see if any other information was hidden under the mat or on the back, and I did find, on the back of the thick paper supporting the watercolor, the beginning of another drawing, but no other markings (see photo). It's difficult to date the watercolor without further information, but I think the frame-watercolor-kraft paper set was original, and given the slightly worn appearance of the frame and the peeling kraft paper, I would date the whole thing to the 70s or 80s. The set is in good overall condition but does show some signs of age: slight stains on the mat (made of white paper), the wooden frame has some marks and discoloration, the watercolor has no stains (what might look like a very slight halo is a thin, light pencil line, the outline of a tree in the background which was not painted with watercolor) but perhaps a very slight yellowing in the upper right, along the mat for 2 mm (or original colors?). The frame measures 41 cm by 29 cm, the watercolor measures 28 cm by 15 cm (for its visible part, because I forgot to measure when I opened the frame).