Des Moines’ Principal Riverwalk is in its final construction season. It has been a long road, and a lot has happened that no one could have predicted when executives of Principal Financial Group Inc. conceived the project a decade ago.

I still recall the news conference on March 19, 2002, when Principal CEO J. Barry Griswell announced that the company would contribute $5 million to $10 million to the first phase, which was expected to cost $15 million to $20 million.

There were delays almost from the start, but eventually the project grew to more than $70 million. By the time it’s finished, Principal’s contribution will be more than $20 million.

The Des Moines-based insurer and its executives deserve a huge thank you for sticking with the project as it expanded to include flood control, an outdoor skating rink, a signature suspension bridge and a stunning new headquarters for the World Food Prize Foundation, among other amenities.

A lot of people deserve credit, but I want to mention three: Griswell for having the vision to launch the effort, current Principal CEO Larry Zimpleman for having the fortitude to stick with it and chief marketing officer Mary O’Keefe for dealing with all the modifications and bureaucratic red tape.

There were also many private donors, including the Ruans, who converted a century-old library into the Norman E. Borlaug Hall of Laureates. The Brenton family helped provide the riverside skating rink. Pioneer Hi-Bred International Inc. created Long Look Gardens at City Hall. The Hubbells are supporting the west-bank kiosk now nearing completion. Hansen Co., MidAmerican Energy Co. and the Bucksbaum family created the pocket park, fountain and sculpture at Second and Grand avenues.

One frustrating thing for everyone is how long everything has taken. A few installations – the skating rink and city hall gardens – were put to use immediately. But most, including the signature suspension bridge above the Center Street dam, won’t be fully appreciated until the whole project is finished.

Most of the delays involved flooding concerns, and flooding continues to be a major obstacle.

In 2002, soon after the original plans were announced, the U.S. Army Corps of Engineers updated flood projections for downtown for the first time since 1975 and boosted the flow rate for a worst-case scenario by 47 percent.

That higher flow rate was used to design the riverwalk, and it added considerable expense and time to the project.

Then, last year when the project was more than 90 percent complete, the Corps recalculated the worst-case scenario and increased the flow rate another 24 percent.

For much of the past year, city officials have been looking for ways to move a worst-case flood more quickly through the downtown area, so they won’t have to build higher floodwalls that would destroy the aesthetics.

Meanwhile, the Corps pulled millions in funding last fall after initial bids for paving, lighting and landscaping came in too high. At the same time, the bad economy caused some private donors to cancel about $1 million in pledges, leaving a total shortfall of about $6 million.

Principal quietly agreed late last year to pick up those expenses so that the riverwalk can continue on schedule.

O’Keefe said earlier this month: “There might be some additional later enhancements, some additional landscaping and such, that the Corps will be asked to pick up in the future.”

But, she said, the walk itself will be completed late this year or early in 2013 with a ribbon cutting planned for next spring.

“We made a promise in 2002 and we’re going to keep it,” O’Keefe said.