A device developed by the Agricultural Research Service (ARS) that tests how well soil resists being eroded by water is helping ensure the efficacy of levees around New Orleans.
The Jet Test Apparatus, designed by Gregory J. Hanson, research leader at the ARS Hydraulic Engineering Research Unit, Stillwater, Okla., uses a water jet pumping at various flow rates to give a rapid determination of the erodibility of soil used in structures like levees.
While the device was originally designed to help evaluate the potential for soil erosion in stream beds and banks, Hanson and U.S. Army Corps of Engineers research civil engineer Johannes L. Wibowo saw the possibility of using the equipment to test new and existing levees. Wibowo is with the USACE Engineer Research and Development Center in Vicksburg, Miss.
The levees in New Orleans' East Parish and St. Bernard Parishboth those that survived Hurricane Katrina intact and those repaired after failingprovided the perfect place to test their idea.
The ARS National Sedimentation Laboratory in Oxford, Miss., which has also been using the Jet Test Apparatus in stream erosion and sedimentation studies, provided the device and training to help the Corps of Engineers with the initial testing of the levees.
Levees that successfully held during Katrina provided a baseline for acceptable erodibility. Newly repaired levees were matched against that standard.
Measuring the ability of the repaired levees to resist water erosion is especially important because the soil being used to rebuild them is from a number of locations around Louisiana and Mississippi, and the soil's resistance to erodibility, once placed and compacted, may not be known.
In the past, there has not been an objective way to measure erodibility, so resistance to erosion has not been included in levee specifications. A report now being finalized by Wibowo may change that, enhancing the future safety of levees and dikes.
ARS is the U.S. Department of Agriculture's chief scientific research agency.