Waterfall looks fine; keep it until some more of the map gets fleshed out and if the style doesn't match then scrap it. Personally, I like it, though. The grass could be that elephant grass which comes up to the shoulder of an elephant. Otherwise, yeah, it's too tall. For now, just go with some green color and some splotches of other colors like tan, light green, etc. I'd hate to suggest using a pattern, I think they mess things up when mixed with hand-drawn elements, but if you could find a good one then, by all means, use it.