Digging Deeper into Dredging

Last week, when I was looking into dredging for a columnon Cedar River flood protection, I asked Ron Fournier, communications chief for the U.S. Army Corps of Engineers at Rock Island, for more information. The possibility of dredging still comes up often around these parts as an alternative to the city's flood protection plan (above).

He did some digging. Pun intended.

Fournier sent me a document issued in 2008 by Stanley Consultants that looked into the feasibility of dredging the Cedar River at Cedar Rapids from the Five-in-One Dam south to just past Mount Trashmore, and its effect on potential flooding. The firm also looked at a much more ambitious effort to both dredge and widen the river channel.

I've posted a copy below.

Stanley comes to the clear conclusion that dredging or widening would be a ton of work,(many, many tons of work) for little benefit.

With dredging only, removing 183,000 cubic yards of sediment and rock from the channel would reduce a 2008-sized flood crest by 0.2 feet. It would cost $26 million, according to Stanley.

And removing a whopping 1.6 million cubic yards of material, including 1.15 million cubic yards from the banks, would reduce a 2008 crest by a maximum of 3.2 feet.

That's more significant, but it also carries an estimated cost of $333 million, while taking a decade or more to complete. One problem is that Cedar's shallow depth precludes the use of big Mississippi-sized dredging equipment. Smaller equipment equals slower progress.

But the bigger problem in both cases is that sediment will continue flowing in. So the effect is temporary. The Army Corps isn't interested in either option.

"Bottom line is that dredging results in limited, temporary flood reduction; benefits do not justify the cost; has negative environmental impacts; and limited benefits are only sustainable with continued dredging which costs would be borne by the City once the project was completed by the federal government," Fournier wrote in an email

Here's the Stanley document:

Dredging S9A S9B - Stanley-Flood Mitigation Options Report (2)