Katrina concluded that the USACE was responsible for the failure of the levees. This was primarily attributed to a decision to use shorter steel sheet pilings during construction in an effort to save money. According to a report published in August 2015 in the official journal of the World Water Council, the Corps misinterpreted the results of a 1985 study and wrongly concluded that sheet piles in the flood walls needed to be driven to depths of only instead of between . That decision saved approximately US$100 million, but significantly reduced overall engineering reliability. In January 2008, Judge Stanwood Duval of the U.S. District Court ruled that despite the Corps' role in the flooding, the agency could not be held financially liable because of sovereign immunity in the Flood Control Act of 1928. Exactly ten years after Katrina, J. David Rogers, lead author of a new report in the official journal of the World Water Council, concluded that the flooding during Katrina "could have been prevented had the corps retained an external review board to double-check its flood-wall designs". Other factors may have contributed to the flooding. According to the authors of Catastrophe in the Making (Island Press, 2009), the straight design and lack of outward flow into the Gulf allowed the Mississippi River-Gulf Outlet Canal to become "the perfect shortcut for salt-water intrusion" which damaged buffering cypress forests and wetlands which historically had protected New Orleans from storm surge. The Army Corps of Engineers built and maintained the canal. Furthermore, according to storm surge researcher Hassan Mashriqui: The Corps of Engineers disputes these causalities. Nonetheless, in June 2008, the Army Corps of Engineers New Orleans District submitted a Deep-Draft De-authorization Study of the MRGO which stated that "an economic evaluation of channel navigation use does not demonstrate a Federal interest in continued operation and maintenance of the channel." Congress ordered the MRGO closed as a direct result. Many of the levees have been reconstructed since Katrina. In reconstructing them, precautions were taken to bring the levees up to modern building code standards and to ensure their safety. For example, in every situation possible, the Corps of Engineers replaced I-walls with T-walls, which have a horizontal concrete base that protects against soil erosion underneath the flood walls. Funding battles continue over the remaining levee improvements. In February 2008, the Bush administration requested that the state of Louisiana pay about $1.5