Flooding along the navigation channel at the Port of Muskogee surpassed projected levels on Thursday, and the Arkansas River is not expected to crest until after midnight Friday.
With a modern record crest at a level of 42.5 feet — nearly three feet higher than what is considered the flood of record — could jeopardize efforts to lower the base flood elevation set for the county by the Federal Emergency Management Agency. A base flood elevation study was undertaken earlier this year by the Muskogee City-County Port Authority in an effort to make more property available for industrial development.
Proponents believed it was possible to lower the base flood elevation from 516 feet by three feet. If the study supports lowering the elevation, property that lies above 513 foot elevation along the Arkansas River and the navigation channel in Muskogee County would be removed from FEMA floodplain maps and made available for development.
Muskogee Port Director Scott Robinson said earlier this year the flood control components of the inland navigation system appear to have performed better than expected. What was considered the flood of record until this week, he said, produced elevations more than four feet below the base flood elevation of 516 feet and maximum flows that fell short of projections used to set that level.
Major flooding that occurred this week after storms dumped several inches of rain across an area that drains into Keystone Lake prompted the release of millions of gallons of water every second from the dam there. All that water, combined with that being carried by the Verdigris River from Oologah Lake and the Grand River from Fort Gibson Lake and other upstream reservoirs inundated the navigation channel at the confluence of three rivers at Muskogee.
Data provided by the National Weather Service showed the Arkansas River at the Port of Muskogee on Monday was at about 498.38 feet — reported as 27 feet at the gauge — when it began its rapid escalation. By 4 p.m. Thursday, according to the National Weather Service in Tulsa, the Port of Muskogee gauge read 42.38 feet.
The 1986 flood crested at 38.6 feet — an elevation of 510.98 — at the Port of Muskogee gauge, according to National Weather Service information. The river is expected to crest Friday at 42.5 feet at the port if conditions remain as they were Wednesday afternoon.
Robinson said earlier this year a reduction of three feet in the base flood elevation would provide significant benefits for local governments, area tribes, commercial developers and private property owners. He said the U.S. Army Corps of Engineers reported on Wednesday the forecasted crest on Friday would result with an elevation of 513.5 feet, about two and a half feet below the present base flood elevation of 516 feet.
"Depending on the accuracy of the information currently available and the rainfall yet to come, if any, this may or may not confirm that a 516 base flood elevation is justified," Robinson said. "I believe it will take time to assimilate all the new information."
A study commissioned by Muskogee County commissioners that was completed in 2005 was used to make a three-foot revision along the Verdigris River. The study by Sheridan Engineering Inc. shows maximum flows from Fort Gibson Reservoir total about a third of the 325,000 cfs used by the Federal Emergency Management Agency to set the base flood elevation at the Port of Muskogee at 516 feet.
The Fourth National Climate Assessment, published in November, noted how changing climate patterns could influence "increases in the magnitude and frequency of heavy precipitation." It cited "multiple episodes of very heavy rain" in Oklahoma and Texas that followed "the abrupt end to the persistent drought in 2015" that caused an estimated $2.16 billion in damage to transportation infrastructure.
"The increasing frequency of extreme precipitation that is projected by climate models is anticipated to contribute to further vulnerability of existing highway infrastructure, although the magnitude and timing of projected precipitation extremes remain uncertain," the authors of the climate assessment state. "As climate conditions continue to change, rare events such as 100-year floods — those that currently have a 1 percent chance of occurring in any given year — are likely to become more common."