Using some masking fluid indicate your birch trees. Indicate the local colors starting with the background foliage area, changing the colors as you go. Below the halfway mark on your paper start to show the river with blue hues. Let dry.
Go in now with middle values and start to build up the foliage shapes, keeping the yellow clean in top of the river. Show rocks by dropping burnt sienna and ultramarine blue in that area and then taking a credit card and scratching the surface. Show an island in the middle of the river with some foliage colors. Drop in some red hues to show more contrast in your colors. Using a credit card scratch out some birch trees. Let dry.
Now using our darkest values show a shadow side on the foliage, usually under the branches. Negatively paint around some of the rocks. Add a darker value blue hue on one side of the river and soften the edges. Scratch in some grasses in the middle island. I added some Gouache to my birch trees to stand out some more, or in the first step you can also use a masking fluid to save the whites. Let dry.