Around deck ground cover, long but shallow area needs filling
We're digging up some rocks around our deck and berming it up to keep the under-deck area from flooding all the time. It's such a pain, all the water goes under the deck as it's leaving the slope of the hill we live on and fills up our window well. When it flash floods, the drain can't empty fast enough and if we don't run a portable sump pump, it cascades through the window and into our finished basement. The other window well was filled in with concrete. I'm looking at berming with a good ground cover to hold it in place rather than doing concrete in this one. The windows are non-functional as there is a huge deck over them.
Anyway, onto the ground cover issue! I was considering Deutzia Nikko (short bloom time is a detractor) or a taller Nepeta Walker's Low (cats are a big detractor). I feel that after the area is bermed, it will drain well but still I worry about a water logged plant. The rest of the time, the plant will probably have mostly dry conditions, partial sun (afternoon sun). The linear feet around the deck is like 40 feet of space to fill, but it's only 12-18" from the driveway to the lattice at the bottom of the deck. Will Nikko make it on such a small amount of space? It seems like it would be the better of the two at keeping the dirt in place.