More from the Corps on upstream impacts, and Tuesday's choice as I see it.

So, where were we? Oh, yeah, upstream.

On Tuesday, I wrote that the Army Corps of Engineers is designing its east-side flood-protection system in Cedar Rapids in such a way that anticipates the eventual construction of a city/state-backed west-side system of levees and walls. The manager of the Corps' east-side project, Tom Heinold. says both-banks protection would have no impact on downstream flooding.

Upstream? The answer is less than perfect.

Here's what the Corps knows. At the north end of the Corps' protection project, in the vicinity of Cedar Lake, both-banks protection would raise the level of a 2008 flood by 3 feet. That's why the Corps' east-side only project, designed to withstand 2008 plus 3 feet, is being built to 2008 plus 6 feet. An extra 3 feet is being added just in case west-side measures are constructed.

To the north of that, the Corps has not conducted a comprehensive study of the potential impact. So at Palo, for instance, we don't know exactly what impact both-banks protection would have on flood levels.

But Heinold said we do know that the impact would be less than 3 feet, potentially much less. Because the highest flood-level rise caused by protection measures, he said, is at the point where those measures begin. From there northward, the impact lessens.

"At the upstream end of the constriction would be the maximum rise in flood heights," Heinold said. "That three-foot effect tapers off to nothing somewhere up river. But what we don't know is just how far upriver."

An upstream impact in places such as Palo is possible. "It certainly wouldn't be three feet," Heinold said. "Much less than three feet."

So we know the Corps does not oppose west-side protection, and is planning for it. We know that the Corps says both-banks protection would not cause more flooding downstream. We don't know exactly what the upstream impact would be, but, according to the Corps, it would be less than 3 feet. If west-side protection is ever built, a comprehensive study and detailed modeling will be required to measure potential upstream impact.

Many opinions are floating around. These are the facts I've been able to gather.

Speaking of opinions, I hear often how the local tax extension vote Tuesday is a plot by downtown interests to grab money for their own protection. It's a big downtown scheme.

Left out of that diatribe is the plain fact that no matter what happens Tuesday, it's still pretty likely that walls and levees will someday be built on the east side of the river. It may take a while, but federal money will shake loose. And the Corps will build it.

"I think it's the smart thing to do," Heinold said of the east side project. "We're proven that there's a cost benefit ratio greater than 1. What that means to me is we can't afford not to do it. That means for every million dollars we spend, we avoid $1.2 million in damages. And that's our taxpayer money being saved during the life of the project."

So really, all that a tax defeat Tuesday guarantees is that the west side will be unprotected indefinitely, dealing a blow to redevelopment efforts. That's it. The pricey hotel won't implode, the mayor won't resign, the library won't evaporate, the amphitheater won't fill up with dirt. All that happens is the west side remains vulnerable to another disaster.

Behind the noise and smoke, charges and counter charges, that's the choice. Protect one side or both.