water loss and preserve freshwater resources along the waterway by reusing water from the basins into the locks. Each lock chamber has three water-saving basins, which reuse 60 percent of the water in each transit. There are a total of nine basins for each of the two lock complexes, and a total of 18 basins for the entire project. The mean sea level at the Pacific side is about higher than that of the Atlantic side due to differences in ocean conditions such as water density and weather. Third set of locks project (expansion) As demand is rising for efficient global shipping of goods, the canal is positioned to be a significant feature of world shipping for the foreseeable future. However, changes in shipping patterns —particularly the increasing numbers of larger-than-Panamax ships— necessitated changes to the canal for it to retain a significant market share. In 2006 it was anticipated that by 2011, 37 percent of the world's container ships would be too large for the present canal, and hence a failure to expand would result in a significant loss of market share. The maximum sustainable capacity of the original canal, given some relatively minor improvement work, was estimated at 340 million PC/UMS tons per year; it was anticipated that this capacity would be reached between 2009 and 2012. Close to 50 percent of transiting vessels were already using the full width of the locks. An enlargement scheme similar to the 1939 Third Lock Scheme, to allow for a greater number of transits and the ability to handle larger ships, had been under consideration for some time, was approved by the government of Panama, The cost was estimated at , and the expansion allowed to double the canal's capacity, allowing more traffic and the passage of longer and wider Post-Panamax ships. The proposal to expand the canal was approved in a national referendum by about 80 percent on October 22, 2006. The canal expansion was built between 2007 and 2016. The expansion plan had two new flights of locks built parallel to, and operated in addition to, the old locks: one east of the existing Gatun locks, and one southwest of the Miraflores locks, each supported by approach channels. Each flight ascends from sea level directly to the level of Gatun Lake; the existing two-stage ascent at Miraflores and Pedro Miguel locks was not replicated. The new lock chambers feature