MIAMI – The latest revision of the Federal Emergency Management Agency (FEMA) FIRM (Flood Insurance Rate Map) maps for Ottawa County in the Grand Lake O' the Cherokees Watershed were discussed and revealed last week.
In a pre-preliminary meeting with key stakeholders held through a webinar, FEMA representatives went over the latest version of the FIRMs, which when adopted as the official maps of the community, will delineate both the special hazard areas and the risk premium zones applicable to Ottawa County and others within the Grand Lake O’ the Cherokees watershed.
FEMA Region 6 Project Monitor Jerry Clark and FEMA Project Engineer Greg Rucker lead the webinar presentation.
The webinar included a brief overview of the project, a summary of community data incorporated into the mapping, highlights of boundary changes revised since the last mapping, and the next steps in the process.
The last FIRM maps for Ottawa County was completed four to five years ago and the new map, which will be implemented in 2018, encompasses more structures and properties. These newly mapped designations can affect the land use, building regulations, and insurance risks.
The August 2016 version was corrected incorporating hydrologic results into the hydrologic model. This resulted in water-surface elevation changes for the Neosho River and a revision of the mapped boundaries of the 1 and 0.2 percent-annual-chance events.
“It was necessary to recalculate the floodway and the good news about this is it resulted in a change to the floodway delineation. Significantly less properties are in the floodway zone than what was there previously,” Rucker said. “We did add approximately 10 structures into this newly delineated floodway, but approximately 200 have been removed from the floodway.”
The floodplain boundaries increased for the 1 percent-annual-chance event. The 0.2 percent-annual-chance boundaries increased in some areas and decreased in others as a result.
Using this data the floodway shifted slightly to the southern side of the Neosho River, resulting in less floodway within the City of Miami's city limits.
“The only revisions made are to the Neosho River model and mapping and to the areas affected by backwater along the area of revision,” Rucker said. “Revisions to the boundaries were relatively minor, but some structures appear to be impacted.”
According to FEMA, approximately 30 times more structures were removed than what were added with the latest revisions.
“While many structures have been removed from the floodway they do still remain in the floodplain, which is important for your communities’ mitigation plans in the future,” Rucker said. ‘It’s important to note that risk doesn’t just stop with the line on the map.”
Floodways are designated areas to keep free of development in order to allow the river to flow down the stream during flooding events, according to Rucker. Floodplains are areas that have a one percent probability of flooding every year (also known as the "100-year floodplain"), and where predicted floodwater elevations above mean sea level have been established. Properties in Zone AE are considered to be at high risk of flooding under the National Flood Insurance Program.
According to FEMA's statistics, there were nine flood disaster declarations in Ottawa County since 2006, seven in Delaware County, six in Mayes and one in Craig County. The increased risk and flood-related disasters declared in each county in the last ten years are factors FEMA says contributed to calling for the re-mapping of the watershed area.
Catastrophic flooding in Ottawa County in July of 2007 and April of 2016 are examples of the flooding FEMA used to determine risk areas.
FEMA's re-map project began in September of 2011 with pre-discovery meetings, followed by the kickoff of Flood Risk Study meetings in 2013. In January of 2016 the results were shown at an initial Flood Risk Review meeting followed by a 60-day comment period, and based on that a revised Flood Risk Review meeting in August 2016 incorporated more feedback.
Last week's meeting offered further review of the latest updates of slight revisions of the FIRMs.
“We did run into some issues and that’s the primary reason for this webinar,” Clark said. “We want to make sure that when the preliminary maps come out that you know what’s on them and you’re not going to be surprised by any of that.”
At the community's request FEMA said this revised version included incorporated data including bathymetry data, high water marks, survey data and cross sections, and hydrologic data to revise stream flows.
“We did have a revision especially in the Miami area along the Neosho River that made some impacts,” Clark said.
FEMA agreed that the unsteady-state model is more accurate for use based on lake conditions, and the model makes results more accurate as it accounts for variations in the rate of water flow.
“It is better fit to the lake conditions and the storage,” Clark said.
FEMA also took into consideration the decrease in water surface elevations citing that in most areas this model resulted in decreases in water surface elevations compared to the draft analysis presented in January 2016, particularly in Wyandotte.
Clark said there were decreases with minor impacts in the latest revision.
Data Used to Determine Flood Risk
Rucker went on to explain engineering used in the latest study conducted in regards to the Ottawa County FIRMs.
Hydrology data incorporated USGS Regression Equations for Oklahoma established in 2010 of the rainfall runoff for the Neosho River, the mean annual rainfall from USDA/NRCS climate prism data, and Digital Elevation Models determined drainage area and channel slope.
Selected streams in high-risk zones were studied of the special flood hazard areas on effective FIRMs and/or streams shown in USGS National Hydrology Data with drainage areas greater than one square mile.
Terrain data used to determine flood risk included the 2011 FEMA LiDAR for the Neosho River/Grand Lake O' the Cherokees and various tributaries in Ottawa and Mayes counties, and 2011 USACE LiDAR for the Town of Afton, Oklahoma Water Resource Board bathymetry, survey 2013 for detailed streams, Tetra Tech Data from April 2016 bathymetry and survey provided by the City of Miami, and USGA topographic maps (10 meter DEMs.)
Update on Craig County
Following the revised Flood Risk Review meeting, the Towns of Welch and Bluejacket submitted elevation data which FEMA claims was not sufficient to make revisions. FEMA has now obtained LiDAR data for Craig County and said with a new more accurate terrain source the preliminary water surface elevations can be delineated and boundary differences can be assessed.
“The investigation is ongoing and a separate discussion with communities of Bluejacket and Welch can be planned,” Clark said.
Projects Next Steps
In the final steps of the process, preliminary FIRM maps will be issued on Oct. 25 to all communities and a 30-day preliminary comment period will begin. The comment period will end on Nov. 24.
In December of 2017 a Community Coordination Outreach meeting will be scheduled with FEMA R6 Flood Mapping and Insurance staff present to assist property owners and stakeholders with the maps and to answer any questions. Comments will then be due within 30 days of the December meeting. Ottawa County FIRM maps will be finalized by June 2018 after letter of notification is received and a 90-day appeal period opened.
The revised Neosho River model has been provided to the City of Miami and Olsson Associates in conjunction with work on Hwy.125 over the Neosho River.