I really like the Dam itself, it really looks like concrete and the intersection with the rock to the left is beautiful!
The only thing that needs improvemend in my opinion is the chanel and its banks below the dam, those need more detail, perhaps more vegetation or maybe diagonal concrete, I think the yellow "sand" which looks ok in the distance is not sufficient for a closeup.
I hope you don´t mind, I couldn´t resist to photoshop, because I think the dam itself is worth to be further developed:

Best regards,
Jan
Sorry, I don´t know how to post thumbs, if you don´t like it I´ll take it away.