<P> The engineers responsible for the design of the canal levees and the I - walls embedded in them overestimated the soil strength, meaning that the soil strength used in the design calculations was greater than what actually existed under and near the levee during Hurricane Katrina . They made unconservative (i.e., erring toward unsafe) interpretations of the data: the soil below the levee was actually weaker than that used in the I - wall design (ASCE: External Review Panel, pg 48). Another critical engineering oversight that led to the failure of the 17th Street Canal involves not taking into account the possibility of a water - filled gap which turned out to be a very important aspect of the failures of the I - walls around New Orleans . "Analysis indicate that, with the presence of a water - filled gap, the factor of safety is about 30 percent lower . Because a factor of safety of 1.3 was used for design, a reduction of 30 percent would reduce the factor of safety to approximately one: a condition of incipient failure ." (ASCE: External Review Panel, pg 51) This meant that the design included a safety factor of 30% ("1.3"), and could cope in theory with stresses 30% more than expected, but the error due to the water gap was about 30%, which immediately used up the entire safety margin, leaving no leeway in the design if any other excess stress occurred . </P> <P> Soil borings in the area of the 17th Street Canal breach showed a layer of peat starting at about 30 feet (9.1 m) below the surface, and ranging from about 5 feet (1.5 m) to 20 feet (6.1 m) thick . Engineers misjudged the strength of the peat which is from the remains of the swamp on which some areas of New Orleans (near Lake Ponchartrain) in the 20th century were built . The shear strength of this peat was found to be very low and it had a high water content . According to Robert Bea, a geotechnical engineer from the University of California, Berkeley, the weak soil made the floodwall very vulnerable to the stresses of a large flood . "At 17th Street, the soil moved laterally, pushing entire wall sections with it...As Katrina's storm surge filled the canal, water pressure rose in the soil underneath the wall and in the peat layer . Water moved through the soil underneath the base of the wall . When the rising pressure and moving water overcame the soil's strength, it suddenly shifted, taking surrounding material--and the wall--with it ." </P> <P> The Federal study was initiated in October 2005, by Lt. Gen. Carl Strock, Chief of Engineers and the Commander of the Corps of Engineers; he established the Interagency Performance Evaluation Task Force (IPET) to "provide credible and objective scientific and engineering answers to fundamental questions about the performance of the hurricane protection and flood damage reduction system in the New Orleans metropolitan area . IPET consisted of independent and recognized experts from the Universities of Maryland, Florida, Notre Dame, and Virginia Polytechnic Institute, the National Oceanic and Atmospheric Administration, the South Florida Water Management District, Harris County Flood Control District (Houston, TX), the United States Department of Agriculture, and the United States Bureau of Reclamation as well as those from USACE . </P> <P> IPET's final findings indicated that, </P>

Where did the levees break during hurricane katrina