Creating ground form meshes from 3D splines

I am trying to create fairly simple terrains such as this one:

I did this by exporting the splines from Autocad into Sketchup and manually creating faces between the ridge line of the banks and the ground lines on either side. Very tedious.

I have tried drawing contours and using sandbox in Sketchup and Terrain object in MAX Design (2011) - the results in both cases were unsatisfactory (inaccurate, and distortion on the flat base plan). I am inexperienced with MAX but I'm sure there must be a way in MAX to create a surface between two 3D splines, but I cannot find it.

Can anyone suggest a good workflow?

thanks

Yes, you can do that with the Terrain modifier in Max, but the accuracy will depend on how many splines you use to define the surface.

Surely there must be some way of creating the banks on either side of the 'ridge' spline, as shown in my clip, without drawing much more. A bit like using edgesurf in autocad? Terrain just creates a bit of a mess. I have used it for broadbrush landscapes, but here where I want a defined shape, I don't think it is the right tool.

3DS Max is not really a great terrain modeling program. It can generate terrain meshes, but as you said, they are a bit messy.

Here's another way to approach terrain modeling: http://www.3dtotal.com/team/Tutorials_2/terrain/terrain_01.php

And another way: http://www.delta3d.org/article.php?story=2005070111291094&topic=tutorials

There are also other programs like Terragen, GroundWiz and Vue that specialize in terrains and landscapes.