help me sequence my yard work..
 

i am slowly re-doing my front lawn. grass is out. i let it all die. i have been round up-ing what is left, and i have removed all of my shrubs. it is essentially a blank slate. i just reserved my lawn tiller. i am going to set it shallow and skim off my dead lawn. then run my simple main water lines off my existing sprinkler solenoids. shallow.

here is my question: i am going to build elevation changes..small hills. three small hills with drought resistant plants. in between the hills, decomposed granite. i'll keep it all separated with that bendable landscape border.

wont my border material overturn with just topsoil on one side? i imagine staking out my borders, wheel barreling in my topsoil, running my irrigation around, covering it all with landscape cardboard, planting, mulching and then bringing in the decomposed granite and tamping it down. can the border hold up the topsoil in the meantime? (like a mini retaining wall?)

i dont want to cross contaminate topsoil over the tidy gravel.

depends on how well supported it is, and how tall the border is

That black plastic stuff that some here have used as air dams?

I hate that crap. You'd think it was easy to work with.

Always frustrates the crap outa me.

Considering you are containing elevation change I'd opt for stone or some pre engineered block.

you are a bridge engineer for godsakes!

Water in topsoil for a couple of weeks to settle/compact/slough----then shovel in your granite.

I'm not sure if anyone uses turf cutters down there, but they make lawn removal a lot easier than a rototiller.
They basically slice off an ~18" wide, two or three inch deep strip of lawn, which you then roll up and dispose of. You're left with a relatively hard and flat dirt surface... much better for putting down gravel, etc.
I rented one to put in a gravel driveway a few years ago... it worked like a charm.

trying to reign back "over-engineering" this...hahaha.

'Disposing' of a perfectly good layer of black topsoil and composted plant matter is a thing of the past.

It sounds like you are in a dry part of the country. If not, now is the time to put in good drainage.

There are no plastic barriers in nature. Why have them in a "natural" yard?