The general shape was easy enough to recreate from the given reference. The shape of the river was changed significantly, but I like how it ended up. The slimmer, snake-like shape feels much more like a river, while the original is more reminiscent of a dam. I also lowered the area that I presume will house the castle, though not for any real reason.
The river took a bit to get right. I had to make it just wide enough to look real, but the smoothing made that hard. I decided to just flatten some of it and make the edges more rigid. The hill was also a little annoying. I still don't think the mountainous terrain next to it looks quite right, but this isn't anything proffesional here.
I think the river bed could be lowered a bit, thinking back on it. Organic, eroded forms are hard to get right. Good thing there's an erosion tool, huh? Actually, I think the entirety of the surface of the area needs a little extra. I think that extra is some noise brush to make everything a little bumpier. This addition would make the whole area less flat (duh), and a little more realistic.
I accidentally textured the whole thing before taking pictures for this reflection, whoops