LONGMONT — The waters of a widened Left Hand Creek spilled over the boulders and under the South Pratt Parkway bridge, a gentle accompaniment to a warm July day near Kanemoto Park.

But more important was where the creek wasn’t going.

Once, a full-on flood might have put 194 homes in its path. Now? More like 25.

Left Hand Creek flood plain project If you go What: A ceremony to mark the end of the Left Hand flood plain project of work will come at a 6:30 p.m. dedication on July 16, in the Kanemoto parking lot. When: 6:30 p.m. Tuesday, July 16 Where: Kanemoto Park parking lot, Missouri Avenue and South Pratt Parkway

That’s what the traffic detours and ripped-up trees were about. And now, after 20 months of work, the Left Hand flood plain project is finally done.

“We view this as a success,” project manager Steve Ransweiler said, watching the flow with satisfaction.

After next week’s dedication, there’s just one detail left: getting the new 100-year flood zone onto the maps of the Federal Emergency Management Agency. Moving at the speed of Washington, that’s likely to come by spring 2014.

“I get calls almost weekly asking ‘Do I still need flood insurance?'” Ransweiler said. “Yes, technically the work is done. But the engineering and acceptance work isn’t.”

A new map helped start things off in 2010. Better contour mapping and a more accurate computer program from the Army Corps of Engineers showed that Longmont’s flood plain was wider than anyone thought — enough to raise the floodwaters by an extra 2 feet upstream of Main Street. Enough to hit 194 homes instead of 112.

Shrinking that down wasn’t going to be cheap. But the city caught a break. During the design of the $6.7 million project, Longmont scored a $3 million grant from FEMA. The rest came from a storm drainage fee voters approved in 2007.

It didn’t kick off without some stormy moments. Concerned neighbors asked for an explanation in 2010 when they received letters saying homes would be “removed from the flood plain;” officials had to clarify that the homes were not being destroyed, but that the plain was shrinking.

The neighbors also had worries about removing a footbridge over the creek, along with about 170 trees.

“I know you’re trying to keep it natural, but how can you do it with fewer trees?” an 11-year-old Meade Halsey-Mendez asked an engineer on the project in April 2010.

The footbridge ended up being replaced rather than erased, but the trees still had to go, both to clear the construction area and to keep the channel from clogging and flooding. In their place, 230 new trees were planted higher up, with young hackberries, oaks and boxelders replacing the elms and cottonwoods.

Those weren’t all the ins and outs. Put together, the changes look like a giant’s shopping list: 30,000 cubic yards of dirt out; 15,000 tons of riprap in; 4,000 tons of boulders placed.

Work began in November 2011. Now after a lot of delays and detours (especially around Missouri Avenue), it’s a map away from true completion.

“It was very much a good thing,” Ransweiler said.

Scott Rochat can be reached at 303-684-5220 or srochat@times-call.com.