AutoCAD Civil 3D :: How To Approach A Full Evaluation Design

i have a site which has a mound in the middle, and quite a few drainage swales running downhill from it, radiating in all directions. i want to calculate a rough estimate of how much fill is required to fill in all those swales (roughly). picture that the existing ridgeline "noses" will be left as is, and the valleys in between are the ones that I want to fill in. the project boundary (toe of slope) is the elevation that I want to hold.

i tried grading tools, and corridors as well, but could not come up with a good way to do this. what I ended up doing is i laid out some feature lines that follow the existing ridgelines down the hill (the banks of the swales), then created a feature line of the project boundary (draped on EG), and a feature line at the top of the mound as the highest elevation, created a TIN from those feature lines so that it triangulates across the swales, and then ran a volume comparison. not the best way i know, but could not think of a better way at that moment.