by Gigi Wood
IOWA CITY – Iowa City’s planning and zoning commission last week discussed changes to floodplain definitions and ordinances at two meetings.
The group discussed it at its informal meeting June 14 and again at their formal meeting June 17.
Bob Miklo, the city’s senior planner, and Julie Tallman, a development regulation specialist for the city, outlined the potential changes for the commission. The city council would ultimately approve or reject any alterations.
Instead of differentiating between 100-year and 500-year flood levels, city staff would like to alter language in city code to refer to both as “flood hazard areas.” Therefore, regulations would be increased to meet risks associated with 500-year floods to minimize damage during future floods.
Flood maps from 1993 and 2008 are generally accurate predictors of damage caused by major floods to the city’s residential, commercial and industrial sectors, Ms. Tallman said. Iowa River flood maps predict there is a 1 percent chance in any given year of reaching 100-year levels, similar to those reached in 1993. There is a 0.2 percent chance in any given year of reaching 500-year levels, similar to those reached in 2008.
The term “flood hazard area” will be used to demonstrate the risk of flooding of any structure in a floodplain, regardless of the 500-year and 100-year designation, as defined by the Flood Insurance Study of Johnson County.
“In generalities, what we’re talking about is taking away the distinction between the 1 percent annual chance and the 0.2 percent annual chance and simply saying, ‘these are all hazard areas, so let’s protect the properties,’” Ms. Tallman said.
A top priority for the city is protecting critical infrastructure, such as hospitals, jails, nursing homes and emergency operations centers, which will be defined as Class 1 Critical Facilities in the code changes. Construction of those structures would be prohibited within floodplains, according to the new language.
If approved, floodplain building standards and elevation requirements would be expanded to include the 500-year floodplain. Any new construction taking place in a floodplain would need to be elevated, or in the case of commercial buildings, elevated or flood-proofed, to 1 foot above the 500-year flood elevation. Depending on where a home or structure is located, that additional elevation could range from a couple of inches to a few feet.
Existing structures in flood hazard areas would be allowed to expand without elevating or flood proofing, as long as the planned expansion would not be larger than 25 percent of the structure’s original floor area, and/or the planned improvements or repairs would not exceed 50 percent of the structure’s current assessed value. When plans exceed those limits, property owners would be required to meet the new standards by elevating or flood proofing to one foot above the 500-year flood elevation.
Flood proofing could be accomplished by using flood-resistant materials such as concrete, waterproof adhesives, pressure-treated lumber and metal doors and window frames.
“Commercial buildings have a little more flexibility than residential buildings, commercial buildings have the option of flood-proofing using water-resistant materials,” she said. “You can’t do that with residential.”
Part of the goal of the ordinance is not only to protect infrastructure but to ensure the safety of emergency responders, who must evacuate residents from homes and other buildings in the floodplain.
Commissioners questioned whether University of Iowa buildings or K-12 schools would be required to follow the new rules. Ms. Tallman said the UI is subject to federal natural resources laws and the school district accepts recommendations from the city.
A few commission members were concerned about how flood-mitigation needs would change once Coralville makes its improvements and the Park Road bridge is elevated, saying it could cause more flooding downstream, in Iowa City.
“To me, it’s just common sense, something’s going to change because that water’s going to go somewhere else,” said Elizabeth Koppes, vice chair of the commission.
The ordinance can be updated as those changes develop, staff members said.
“It’s not only the Iowa River which would be impacted by Coralville, there are five or six streams that are in that area, so if we admit to some degree of not knowing the impact of Coralville’s plans, we can look at Ralston Creek, for instance and we’ll get a difference, although they’re not as dramatic,” Ms. Tallman said.