NWS: heavy rainfall at Bennington was ‘Once in 1,000 years’ event

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NWS: heavy rainfall at Bennington was ‘Once in 1,000 years’ event

  Once in a thousand years.

  That’s how rare the National Weather Service says that the flooding event of September 3rd in the Bennington area was.

  Officials from the National Weather Service came to Switzerland County recently to observe the aftermath of the storm that caused severe flooding and countless damage — and after than analysis, another team arrived to take a longer look into just how rare an occurrence like what happened here was.

  The National Weather Service then issued a report to the county on the storm, and covered both Switzerland County and areas of Jefferson County where the epicenter of the storm was centered.

  Some of the observations by the National Weather Service:

  • “On the late afternoon/evening of September 3, a southward to northward moving storm positioned itself over the Indian Creek basin of western Switzerland County, Indiana. While radar estimated that the Indian Creek basin received the worst of the heavy rain, some of the heavy rainfall footprint also fell into the Indian-Kentuck Creek and Lost Fork which flow into Jefferson County, Indiana.”

  • “By 7:00 p.m. EDT, the 6 hour radar estimated rainfall indicated a large area of 3” to as much as 10” or more fell from Mt. Sterling to Bennington, with Bennington being at the center of the heaviest estimated rainfall.”

  • The report includes an image of the radar for the area during the storm, and in the center a white square over Bennington shows 9-10-inches in six hours —but in the center of the white square is an area of purple that raises that rainfall total to 10-11-inches over the same time period. The heaviest rain was concentrated in a very small geographic area, which heightened the potential for damage.

  • Included in the report is a table created by the National Oceanic and Atmospheric Administration (NOAA). That table identified the historic frequency of an occurrence of a rain event like the one here.

  • “Rainfall Rarity: The table below is form the NOAA Precipitation Frequency Atlas, which identifies the historic frequency of occurrence of such a rain event. The column at the far right is the ‘1,000 year’ rainfall event occurrence (meaning the ‘odds’ of this rainfall occurring in nay given year is 1 in 1,000).

  “Note that for the 3 hour duration/6 hour duration/12 hour/24 hour duration —the ‘1,000 year’ rain is 5.30-inches, 6.46-inches, 7.33-inches, and 8.34-inches respectfully.”

  • So, according to the NOAA chart, a once in 1,000 year amount of rainfall in a six hour period is 6.47-inches. On Saturday, September 3rd, the Bennington area of Switzerland County got nearly twice that much.

  • The report: “For more perspective of the rarity of this rainfall — there was a volunteer observer who reported 9.40-inches of rainfall in NW Switzerland County. This volunteer network (CoCoRaHS) reports the 24-hour rain gauge values once a day. So not that the 9.40-inches exceeds the ‘1,000 year’ 24-hour rainfall per the frequency tables.”

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  The past week has been one of repair and evaluation for county officials and the county highway department.

  Switzerland County Highway Superintendent Anthony Thomas said that most of the roads that were closed or limited last week have now re-opened to traffic.

  “Most of the roads are passable,” Thomas said. “The lower end of Drake’s Ridge is still closed; and the lower end of Sergeant Booker is closed. We’ve got a contractor coming to clean the debris off of Smith’s Ridge and Parks Ridge bridges. We’re still assessing all of the damage that we’ve got. It’s an ongoing thing.”

  Thomas said that no official status for the bridges where Parks Ridge and Smith’s Ridge intersect with Bennington Pike; noting that once they are cleared off from debris, the bridge inspector will then come and evaluate the bridges structurally before any determination can be made as to whether or not the bridges will need to be replaced.

  Thomas said that County Highway workers were working on Kelly Road on Monday, working on culverts and trying to get the dry fords cleaned off.

  “It’s going to be a process,” Thomas said. “Kelly Road is open. We’re just cleaning the rocks out of the dry fords so that the water can get through in case we do get another rain. They’re completely plugged. All the culverts and pipes are plugged on these dry fords, we’re trying to get those cleaned out and clean some ditches out so the water’s got somewhere to go if it does come another heavy rain.”

  As has been noted since the storm, motorists who don’t need to be in the Bennington Pike area should avoid it if possible; or use caution when traveling in that area because of the work being done and the workers who are doing it.

Have Flood Damage?

  Switzerland County residents impacted by flash flooding that occurred on September 3rd, are asked to contact Indiana 211 to report damages and help with a damage assessment. Indiana 211 asks residents to utilize the online submission rather than calling Indiana 211, which is receiving a high call volume currently. Reach Indiana 211 online at: https://in211.communityos.org/isdh_damage_report_switzerland