USACE Modeling Errors impact on St. Tammany Parish

September 21, 2020

The Corps has finally released their surge models that show the south shore barriers have significantly affected the surge risk in St. Tammany Parish.

Before Congress authorizes an additional $3.2 Billion to repair the sinking Orleans levee system (HSDRRS), the Corps has an ethical obligation to correct the damage the HSDRRS has done to St. Tammany Parish. 

St. Tammany surge protection projects require fast tracking.  We cannot wait another 15 years or even another 5 years; we need protection now.  The construction of a gate at the Eden Isles marina can be built immediately and provide significant protection.  Additional upgrades can follow (such as increasing the elevation of Hwy. 11 and Lakeview Dr.).

Tom Thompson

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Supporting documentation:

November 2012,

Corps held a public meeting to present their finding on HSDRRS flood impact from hurricane Isaac.  At the meeting, Colonel Fleming, Commander of the Corps’ New Orleans District Office, stated the Corps has a policy of accepting responsibility to mitigate problems their projects cause.

https://www.youtube.com/watch?v=e-JEK7cF4EQ&feature=youtu.be

As of this date, the Corps has not admitted to, or accepted responsibility for, increased flood risk caused by their structures

April 2013,

Corps agreed to model Lake Pontchartrain surge differences with and without the HSDRRS, and release their findings in November 2013.  Instead, the Corps withheld this vital information for 5 years until a Freedom of Information Act (FOIA) forced the Corps to release their impact findings. 

Once the models were released in 2018, they were found to be extremely inaccurate and “significantly” underestimated the HSDRRS impact on St. Tammany Parish.

See attached: “2013 April Corps' CED Response Letter”

March 2018,

A Freedom of Information Act (FOIA) request was made to release the Corps’ Evaluation of Storm Surge with and without the HSDRRS.

June 2018,

The Corps of Engineers denied the FOIA request to release their HSDRRS impact report, claiming “deliberative process privilege”.

July 2018,

A Freedom of Information Act FOIA appeal request was made to release the Corps’ Evaluation of Storm Surge with and without the HSDRRS.

August 2018,

In response to the FOIA appeal, the Corps of Engineers released their evaluation of storm surge outside of the HSDRRS.  The report contained inaccurate topographic data in their baseline 1965 model (pre-HSDRRS).  The Corps modeled a nonexistent, 14 foot high levee that reduced Lake Pontchartrain’s 1965 outflow opening from a 12 miles to a 6 miles.  This incorrect modeling data was used to support false statements that the HSDRRS had little impact on St. Tammany Parish.

See attached: “Errors found in 2018 August Model”

January 2020,

Based upon comments received, the Corps of Engineers revised their original HSDRRS impact study by issuing an Appendix D to correct the 1965 baseline model and their findings.

The corrected 1965 model, removed the nonexistent 14 foot high levee, but replaced it with a 9 foot high railroad embankment that Corps’ documents said could not function as a levee.  The railroad embankment also incorrectly restricted Lake Pontchartrain’s outflow opening from 12 miles to 6 miles.

See attached: “Errors found in 2020 January Model”

February 2020,

Based upon comments received, the Corps of Engineers once again revised their HSDRRS impact study and removed the railroad embankment structure, which increased Lake Pontchartrain’s 1965 outflow opening from 6 miles to 12 miles and re-issued Appendix D.

This revised study shows the HSDRRS has increase storm surge by approximately 5” at Eden Isles and roughly 8 to 10” between Slidell and Pearlington (See page 8 of 14 of the Appendix D revision)* 

See attached: “2020 February Corps response to errors”

See attached: “2020 February Revised model Data APPENDIX D”

* Note: an increase of less than 6” to Mississippi was significant enough to stop the Corps’ consideration of the CPRA’s Barrier Plan.  (See: Coastal Protection and Restoration Authority of Louisiana (CPRA) Lake Pontchartrain Barrier Evaluation Technical Report February 1, 2016).

Despite Corps’ models showing HSDRRS impact to St. Tammany Parish, the Corps has not admitted the impact to St. Tammany Parish or committed to mitigating/alleviating the increased surge into St. Tammany Parish.

This is why Congress should extend HSDRRS protection to St. Tammany Parish and include St. Tammany Parish protection into any additional HSDRRS funding request.