Posted on August 9, 2016
By Andrew Casler, ithacajournal
Five years after a study found Ithaca’s flood control system would fail during the type of rain storm engineers designed it to protect against — remedies for the potential flooding remain years away and underfunded.
Sediment has filled so much of the flood control system the waterway would fail during a 100-year storm, sending floodwater pouring through the city, according to a 2011 U.S. Army Corps of Engineers analysis.
City of Ithaca officials say they’re still working with New York State to dredge the waterway, but it remains unclear when work will begin.
“I have answered that question so many times with so many different dates; I’m afraid to even venture a guess,” City of Ithaca senior planner Lisa Nicholas said during a May 11 city meeting. “We’ve told the public so many times, ‘It’ll be next year’ and that was all based on what we thought was going to happen with the DEC, but it hasn’t.”
The state Department of Environmental Conservation is primarily responsible for dredging.
Last year, DEC spokesman Peter Constantakes told The Ithaca Journal construction on a sediment management facility would begin in spring 2017. DEC would use the facility to dry sediment it dredges from the inlet.
Once the DEC builds the facility, dredging could start in fall 2017 or spring 2018 at earliest, he said.
During the May 11 meeting, Nicholas made it clear the process could be further delayed.
“If we stay focused and we keep working with (DEC), possibly they could dredge in 2018,” she said.
The DEC did not respond to recent requests for comment on this issue.
The persisting threat was the subject of a July 2015 Ithaca Journal watchdog report, titled, “Clogged inlet creates flooding hazard.”
Total assessed value of properties threatened by the flooding was $421 million in 2013, according City of Ithaca documents.
This potential flooding threatens commercial properties with a total assessed value of more than $245 million, industrial development assessed at $9 million, more than 600 dwelling units, four churches and one BOCES school, according to the city.
Once DEC builds the dredging infrastructure, the question of whether there’s enough money to fully dredge the flood control system remains unanswered, according to Nicholas.
New York state allocated $13 million for dredging, and in January $2 million of that money had been spent to design the dredging program, she said.
Sediment management facility construction is estimated to cost about $4 million, which leaves about $6 million to actually dredge, according to Nicholas.
“We think for $6 million, they’re going to be able to dredge about 160 cubic yards of sediment,” she said.
The 2011 Army Corps analysis, however, called for removing approximately 660,000 cubic yards of sediment to restore the flood control channel.
It’s unlikely the inlet will ever be restored to its design depth, Nicholas said.
“What we’re trying to do is focus on getting some sediment out, and making it more navigable (for watercraft).”
Any amount of dredging will have an impact on flood control, she added. The city has an additional $2 million to dredge Cascadilla Creek, according to Nicholas.
“We’re doing our own study, and really the question of how much has to be taken out to restore (the inlet systems) flood control properties is still really an (unanswered) question,” she said. “We don’t need to restore the whole thing in order to have some impact on flood control.”
New flood maps
As Ithaca officials await dredging, city Public Works Superintendent Michael Thorne is working to update Ithaca’s Federal Emergency Management Agency flood maps. He began the flood mapping effort in 2015.
The new flood maps will likely show more extensive potential flooding than the 2011 Army Corps analysis, Thorne said.
“We’re going to be looking at the flood profiles of Cascadilla, Fall Creek, Six Mile Creek and the Cayuga Inlet,” he said.
The Army Corps looked at only the Cayuga Lake inlet levee system, and it didn’t account for the effect of lake levels, he added.
The city’s study will evaluate flood threats from storms likely to hit every two, 10, 50, 100 and 500 years, he added. The study would also account for the effect of lake levels on flooding in the city.
“We’re going to be modeling those five different storms under three different lake levels, so essentially we’ll have 15 flood profiles for different conditions,” Thorne said.
The work is behind schedule, however. Researchers need to measure stream flows during heavy storms to create the flood models.
“We were assuming we’d get some heavy storms this summer, and that the flood-mapping effort would be done by the end of this year or early 2017, but if we don’t get heavy rainfall or flows in the creek, it may be pushed back a little bit further,” he said.
Thorne plans to deliver the new flood maps about six months after the city is hit by several severe storms, he added.
‘Ticking bomb’
The U.S. Army Corps of Engineers built the flood control channel after two major flood events — deemed 100-year storms — swamped large areas within the city in 1935 and 1956.
July 8 marked the 81-year anniversary of flooding from the 1935 storm. The storm is estimated to have killed more than 100 people across the state and, in the City of Ithaca, caused $26.4 million in damage, adjusted for inflation.
In spring 1956, the second flood caused an estimated $271,500 in damage. Adjusting for inflation, the cost in 2016 would be $2.4 million.
Ithaca Alderman Seph Murtagh, D-2nd Ward, said past flooding has led to a public sense Ithaca is a “ticking bomb” for severe flooding when the next 100-year storm hits.
In some cases, Ithaca has dodged intense storms and flooding, such as the devastating June 2015 storm that flooded parts of Newfield. But in January 2014, ice jams and shallow waterways on Cascadilla Creek inundated parts of Ithaca’s Fall Creek and Northside neighborhoods as water poured into basements and onto roadways.
“People constantly bring it up,” he said. “There’s this sense that we’ve dodged a bullet a little bit, but especially if we were to get a 100-year flood … that’s kind of the nightmare scenario that people have in their minds, and I think that’s one of the reasons we want to get this taken care of.”
Source: ithacajournal
