Answer: Your plan to rinse the pebbles is a good one. Not only will you remove the soil, you'll also wash away any weed seeds lurking within! I'd use woven weed barrier (or landscape cloth) so that dust that accumulates on your river rock and pebbles can be washed away with the hose. (I've seen landscape cloth in both lightweight plastic and woven/spun fabric - either would allow most of the soil particles to drain out, providing you rinsed the rock often enough to keep accumulated dirt to a minimum.) Even with routine maintenance you'll probably need to disassemble and clean your dry creek bed every five years or so.
Laying the landscape cloth shouldn't present much of a problem - rake the area smooth, lay the cloth down, cutting to shape or turning under the edges, then lay your large rocks and work the pebbles in between the rocks. They'll settle down to fill in the gaps, so you may need to add more pebbles as time goes on. Hope this info helps!
Q&A Library Searching Tips