Make a line drawing of the shape of the bridge. It is an interesting optical illusion, with bricks at varying angles and the top row at a diagonal. It is always a good challenge to paint a bridge in perspective: the archway underneath should give a 3D effect to your initial drawing.
Do not draw in too many lines for bricks etc otherwise your sketch will morph into a drawing. Mark in lightly the waterline.
If you keep all your palettes, like I do, these make the perfect vehicle for painting the bridge. If not, you will need purple, blue, brown and a yellow, but you will be using them in varying degrees of tone and so you need to mix a good variety. Use a large brush to wet the bridge area, let that soak into the paper, and rewet. Let it soak in: you want the paper to stay wet to damp while you work. Apply a wash of purple, and mingle in some blue, randomly, as you work apply stronger mixes of your colour, use a variety of brushstrokes and then mark in some lines for the bricks. I impress drew some in also to give different effect but also to suggest some light source. This should take you around 20 minutes to paint.
Add the green foliage, using three different greens from light to dark. Underpaint the background with a light yellow: this is an essential part of this painting. If you do not and start applying greens they will appear too close. Have a wide range of greens ready, from light to a dark that looks almost black. I mixed a dark green with a dark red, you can make such wonderful green colours, it is an endless pleasure for any painter to make these wonderful green colours.
I started in the top left hand corner, I impressed some lines on to a light green mix to suggest distant trees. I used a wide range of brushes to create a combination of small to large brush strokes. If you like using a sponge, that would be useful too, but I prefer making my own mark.
Under the bridge: use a brown over any washes you have applied to suggest a lack of light. You can work in the same way for the greenery, to suggest a wide variety of plant life.
The body of water: I used glazing and also line to create a sense of murky water. I wet the paper, applied a wash of green, horizontal brushstrokes. When that was dried I painted in vertical lines of darker green and brown. I then applied some curved line to suggest the reflection of the set of steps.
I mentioned previously, you would need a yellow for the bridge. There is a technique you should use when you want to suggest a light source and that is glazing with a yellow wash when your painting is complete. I glazed parts of the bridge with a yellow wash, using a large brush and quick brushstrokes. This is a technique that can add further light to any watercolour painting. Try this on an old painting you may have done some time ago that you do not regard as an important part of your portfolio: this technique may make it so!
This painting took about 10 hours to complete, a very pleasant painting experience.