Surface colour aligned to terrain artifacting

[Anonymous User]

I have a question about aligning a surface colour to terrain modification.

I have a terrain file and associated .tiff. Now I would like to modify this terrain, as there is a little basin in the reserve I am modeling.

Please see the attached images.

The green is a shapefile from CAD, which I have given a green colour. When flat it displays correctly. However, after I adjusted the terrain, when I align the shape to the (new) terrain shape, this happens. It becomes all ugly.

This also happens to the vegetation shapes around the edge, when aligned to terrain.

This image shows the manipulation of the terrain. It's only 1.5m deep, so only a slight variation.

.

Does anyone know how to stop this from happening?