LSU Hurricane Center director Ivor van Heerden had warned of severe flooding due to loss of coastal wetlands. However, this modeling and predictions had assumed the levees would perform. They did not. Levees designed and built by the Army Corps failed three feet below design specifications (main basin of New Orleans) and eroded because they were constructed with sand instead of clay (east New Orleans). According to a conservative 2007 study by the American Society of Civil Engineers (ASCE), the majority of the damage from the flooding was due to the levees failing. And this majority figure is property loss only (residential and commercial capital) and does not consider damage to infrastructure and public utilities. [page 39] On August 25, 2006, Lt Gen Carl Strock conceded that “better communication from the Corps of the risk associated with the existing levee system might have spurred more people to evacuate” in advance of Katrina.