Iowa City making changes to floodplain standards

Iowa City is on its way to having tighter standards for construction in floodplains.

The City Council Monday night voted 6-0 in support of the first reading of an ordinance dealing with floodplain standards and definitions. Ross Wilburn was absent. Two more readings are necessary for the ordinance to be approved.

The city's current ordinance is written to meet the risks of a 100-year flood. The changes would increase that to 500-year-flood levels. The 2008 flood reached the 500-year boundaries in Iowa City.

New and substantially improved structures would need to be elevated at least one foot above the 500-year flood levels. Commercial buildings could be elevated or flood proofed.

The elevation difference between the old and new standards would be minimal to up to four and half feet, depending on the location in Iowa City.

The ordinance also would discontinue the use of the terms “100-year” and “500-year” floods, saying they are misleading. That's something Iowans who went through the 1993 and 2008 floods know all too well.

A 100-year flood has a 1 percent chance of occurring in any given year, and a 500-flood has a 0.2 percent chance. The city would use those percentages when referring to those levels of flooding and also call those flood boundaries a “flood hazard area.”