Flat area

[EdBardet]

What is the easiest way to have a flat area in a terrain. Basically I want an irregular flat area to represent a delta at the confluence of a river and the sea.
Thank you,
Ed

[Dune]

You can use a simple shape as a mask to blend the hilly terrain out. Irregularity you can get by warping that simple shape. There's a clip file or tgd somewhere on the forum of an island I once made using this method.
Or use a mask made in Photoshop (greyscale will do)