Parallel vectors from Terrain

Hello,

I am trying to determine vectors that relate the height map information from a Terrain built in Unity to vectors that are parallel to the slope of the terrain.

i.e. From the Unity built terrain, whose contour map looks like the one in the Figure below, I want to draw the vector which is along the slope of the terrain, in the direction that is perpendicular to the contour lines.

How would I do this? I've found a question here that includes an answer which supplies code to find the contour lines from a height map.

Does any one know how to find the vector's though?

Thanks.