The full scope of a project aimed to prevent roughly 200 Highland properties from being included in a flood map was presented to the city council this week.
The Federal Emergency Management Agency (FEMA) periodically updates its flood maps to take into account new developments, changes in topography, etc., and how those changes may put surrounding areas at a greater risk for flooding.
In 2017, Highland officials began studying potential problem areas when on preliminary flood maps FEMA released to replace those created in 1986.
Those drafts tripled the 1986 floodplains, increasing the number of “high-risk” parcels from 135 to 365 and showed flood elevation upstream of the CSX railroad of about 6 and a half feet, adding roughly 100 acres to the floodplain.
The parcels of land that could be affected stretch throughout the city, starting from Troxler Avenue and running south toward Highway 40, in some cases even covering the highway. Also affected would be a large number of parcels north and northwest of the CSX Railroad also could be affected.
Owners of those endangered parcels likely would see major increases to their insurance premiums. Also, new structures built within the area would be subject to increased standards that would add expense to — and potentially discourage — future development.
The city contracted the engineering firm of Oates Associates to search for the cause of the expanding floodplains and find a solution.
David Oates, Oates Associates’ chairman, said two major factors shaped FEMA’s decision on the flood maps: a culvert that was cutting off water flow downstream and a discrepancy with the flow rate of water heading toward the affected areas.
The 100-year-old culvert, a drain that allows water to flow under the CSX Railroad, had been altered, reducing by half the volume of water that can pass through it.
He said replacing culvert, located at the train crossing at Poplar Street near U.S. 40, could keep approximately 200 parcels of land out of the flood zone. The railroad’s approval was necessary for the construction, which the city received.
Oates Associates created a new flood map factoring the corrected flow rate with new culvert. That preliminary map, which Oates said FEMA has agreed to, significantly cuts the acreage that will be added to the flood zones from 103 to 31.
He added that both parties agreed the proposed water flow rates are more accurate than FEMA’s preliminary maps.
“Those two things together have an impact of lowering the flood elevation four feet or so,” Oates said. “It significantly reduces the flood plain.”
Oates said the culvert project is ready to go out for bid, and could be reach for council approval within the next few meetings.
Oates said the city needs to act quickly on the project, however, because of the unpredictable timetable in which FEMA will finalize the new maps. He said the question of when the map work will begin has been asked many times with no concrete answer.
“FEMA is not actively working on this,” Oates said. “They agreed with the concept — agreed that reducing flows and an increase in culvert size should significantly reduce the floodplain — but they won’t release any new data until they get funding to do more studies and the culvert is complete.”
City Manager Mark Latham said this project ranks higher than most in Highland because of the large impact it would have on residents within the floodplain. If the preliminary maps were to go into effect, homeowners could pay thousands in flood insurance.
The project will cost roughly $500,000, part of which the city hopes the railroad will help fund.