City staff propose corrections to Perryman Ditch drainage maps; dozens of properties removed from regulatory floodplain

City of Tulsa staff presented a resolution to amend portions of the previously adopted Perryman Ditch master drainage plan and to update the City of Tulsa regulatory floodplain and drainage-sensitive-area maps (atlas panels 46, 47, 51 and 52).

Joan Gosvick of the Water and Sewer Department told the committee the master drainage plan’s technical consultant had identified areas that do not meet the 40-acre drainage-area threshold the city uses when mapping regulatory floodplain. “Per title 11A, when we map the City of Tulsa regulatory floodplain, we don't map anything that has less than 40 acres,” Gosvick said. She described the corrections as removing shaded areas on the atlas panels that should not have been included under the city’s mapping rules.

Gosvick said the correction will remove 29 structures from the City of Tulsa regulatory floodplain and 32 structures from drainage-sensitive-area requirements; she added the revision “adds 6 less” (clarification: the transcript phrasing was that the net change differs between the two lists). She explained the difference between the two map designations: the regulatory floodplain carries the “substantial improvement” threshold, meaning a structure that is improved more than 50% triggers limitations, whereas the drainage-sensitive-area designation generally carries development requirements but without the substantial-improvement prohibition.

The Perryman master drainage plan also contains more detailed hydraulic modeling, Gosvick said, which refined base flood elevations. She gave an example comparing prior mapping that used “3 foot or less” ponding assumptions to more precise modeled depths: when base flood elevation is lower (for example 6 inches), required building elevation above the base flood changes accordingly (the city’s one-foot-plus requirement would result in a smaller finished-floor elevation than the prior three-foot assumption).

Committee members asked whether removal from the regulatory floodplain means an area will no longer flood. Gosvick said removal does not eliminate flood risk: properties will still flood under storms larger or different from the modeled 100-year event. She said owners can still purchase flood insurance and remain eligible for policy discounts, but their insurance rating and regulatory obligations will change because they are outside the mapped 100-year regulatory floodplain.

Members pressed staff on what the revisions mean for residents’ ability to make improvements and for the city’s capital improvement program to address flooding. Gosvick said the master plan identified projects that are now in the city’s stormwater CIP; committee members noted that the department’s current CIP inventory for stormwater totaled about $2.4 billion and the city budgets roughly $5 million to $10 million annually for those needs. Members and staff discussed short-term and long-term tradeoffs including acquisitions, holding ponds and underground storage as potential but costly options.

The resolution text presented to the committee states the corrected atlas panels are adopted as the official regulatory floodplain and drainage-sensitive-area maps for the part of Tulsa County within city limits, superseding maps adopted Aug. 4, 2024, and that electronic atlas copies may be filed in the city clerk’s office. The transcript records the presentation and discussion; it does not record a committee roll-call vote or final outcome in the committee meeting minutes that were provided for this article.