Creating a design surface to calculate proposed volumes

[tyler.lehman]

I am fairly new to 3d work, and we are working for a company that is doing levee repair. I have created the existing surfaces, centerlines, alignments, create all the cross sections. I don't know the best and most accurate way to create what the design surface is and have it line up with the existing. we are laying rip-rap along the base of a washed out levee, and the design specifies an 18" "shelf" at a certain elevation, then a 2-1 slope down to existing grade in the creek. i need to be able to create the surface for the design that will automatically close on the existing surface and plot in my cross sections to give me volumes of material to be used.