Terrain Clamping

Hello.

So, after some experimetning I managed to get a script generating a fairly simple terrain with serveral perlin noise layers. Here's the script:

 using UnityEngine;
 using System.Collections;
 
 public class TerrainGenerator : MonoBehaviour {
 
 
     public Terrain terr;
 
     private float frequency;
 
     private float amplitude;
 
     private int Warstwy = 20;
 
     public NoiseLayer[] noiseLayers;
     
     void Start () {
     
     terr.heightmapMaximumLOD = 0;
 
         noiseLayers = new NoiseLayer[Warstwy];
         float frequency = .008f;
         float amplitude = 0.085f;
         for( int n=0; n<noiseLayers.Length; ++n)
         {
             noiseLayers[n] = new NoiseLayer();
             noiseLayers[n].frequency = frequency;
             noiseLayers[n].amplitude = amplitude;
             
             amplitude *= 0.5f;
             frequency *= 2f;
             
         }
 
 
         int xRes = terr.terrainData.heightmapWidth ;
         int zRes = terr.terrainData.heightmapHeight ;
         
         float [,] heights = new float[ xRes, zRes];
         
         for(int z = 0; z < zRes; z++){
             
             for(int x = 0; x < xRes; x++){
                 
                 float height = 0;
                 foreach(NoiseLayer noiseLayer in noiseLayers)
                 {
                     float f = noiseLayer.frequency;
                     float a = noiseLayer.amplitude;
 
                     height += Mathf.PerlinNoise(x*f, z*f) * a;
 
                 }
             
 
                 heights[x,z] = height;
 
                 
                 
                 
             }
             
         }
 
 
 
 
         terr.terrainData.SetHeights(0,0,heights);
 
 
 
         
 
     }
     }
 }

And here's a typical result:

Now, I have several questions. First, how can I get a clamp height effect shown in this video?

http://www.youtube.com/watch?v=mXTxQko-JH0

Second: The terrain looks fine, but is there a way to have somethin like biomes? Like, in one area there would be for example mountains, in another hills and they would all blend together nicely. I heard something about Voronoi diagram, but i don't know how to implement it in my code/use it.

Thanks in advance for all the answers.

-Xentarok

P.S: If you have any questions aks them in the comments.

P.S.2: English isn't my native language so I apologize for any mistakes.