Oktibbeha: another landslide induced threat to an earthen dam

In Mississippi, USA attempts are underway to lower the lake level behind the Oktibbeha County Lake dam (location 33.509, -88.944), which is described as being in imminent danger of collapse.  Reports suggest that an inspection of the dam at 7 am on Tuesday indicated that a significant landslide had occurred on the downstream face.  A further inspection four hours later found that substantial further deterioration had occurred.  This image, from Starkville Daily News, shows the extent of the landslide:-

The ongoing landslide on the downstream face of the Oktibbeha dam in Mississippi, USA. Image from the MEMA Coordinator via the Starkville Daily News.

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Attempts are now underway to lower the level of the lake using siphons too supplement the spillway, but further rainfall is forecast in the coming days.  The local residents have been advised to evacuate, although at the moment this is not mandatory.

Ongoing problems with the Oktibbeha dam

This is not the first time that the Oktibbeha dam has faced problems.  An inspection in 2016 rated the dam condition as “fair”, whilst a further report in February 2019 identified ongoing seepage problems with the structure.  The Starkville Daily News reports that the ongoing failure has occurred at the same location as other slope problems, and a slope repair was also required in 2016 and in 2017.  In September there were discussions about the need for the replacement of the levee, and State level funds were sought to renew the dam as “the waters of Oktibbeha County Lake Dam could pose danger to nearby residents if the levee is not replaced”.  However, the costs of this work are around $8 million – as the image below shows, this is not a small structure:-

Google Earth image of the Oktibbeha County Lake in Mississippi.

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Once again, this incident highlights the fragility that is being created by the legacy of ageing infrastructure with inadequate resource being committed to upgrades.  The impacts of a collapse, which will hopefully be avoided this time, would be substantial.  Interesting, the Star Tribune report includes the following:-

There have been at least two other dam failures in the South after heavy rains within the past month.

Holmes Lake Dam in Hinds County, Mississippi, failed Jan. 2. Some vehicles were damaged, but no injuries were reported. A post-failure inspection indicated that faulty construction may have allowed internal erosion of the earthen dam, said Willie McKercher, chief of the Dam Safety Division at the Mississippi Department of Environmental Quality.

A pond swollen by heavy rains broke through a dam in Aiken County, South Carolina, on Dec. 23, damaging several vehicles but causing no injuries.