Creating a smooth terrain from terrain skirts automatically

[Ultratimsil]

i have created a terrain out of lines i took from a reference, the lines had multiple nods, and when i finished it create a stair like terrain and not smooth, so i have been doing it manually. 

as you can see in the picture the left side is what i did manually and on the right you can see the stair like terrain that i will be working on. is there a better method or an initiall approach i should take to avoid this amount of manual work?

Operating system used: Windows