JNJ wrote:

...I'm
going to terrace the back a bit, put in some small walls (about 2-3 feet
tall each) to handle some drainage issues -- I plan on grabbing this run off
in some barrels for later use in the yard (save $$ from the water works!)...




Barrels won't do it. You should consider building a cistern or a small
pond. A one inch rainfall on 1000 square feet of area is 144,000 cubic
inches of water, which translates to more than 600 gallons. That means
you need a lot of barrels, and you have to plumb them together to make
use of the water. Building a pond and lining it with plastic sounds like
much less work to me, and is probably more attractive than a back yard
full of barrels.