I work in south Longmont. Where I cross the Boulder Creek, it's usually 3 meters wide and so shallow the rocks on the bottom emerge from the surface of the water. When I was hauling out yesterday after our workplace got an evacuation notice, the creek was a kilometer wide, backed up against the bridge, which is probably 15 meters wide by two meters deep.
Longmont spent eighteen months reworking the Lefthand Creek drainage, deepening it and tearing out all the trees beside it, through the middle of the city. At the time, local citizens were outraged at the expense, writing nasty letters to the newspaper and showing up at city council meetings yelling about what a waste of money it was and how debit spending was the devil. Lefthand filled right up to the top and moved like a freight train, but didn't overtop through much of the town. The place where they stopped the rework, and the creek returns to its shallow, cottonwood-tree-filled drainage, is where it spread out and started flooding basements, according to pictures my friends who live there are sending me. I'm hoping this experience will motivate the city of Boulder to do the same for Boulder Creek. One of my friends lived in a house across from Naropa University, right beside Boulder Creek, that had a big metal sign on the front warning the inhabitants that they lived in a flood zone. That should never happen. That should be parkland, not places where kids live. (She moved, thankfully, because that house had close to two meters of water in the main floor, from pictures I've seen, and I'd hate for her and her two toddlers to still be living there.)