The average depth of the Seine today at Paris is about nine and a half meters. Until locks were installed to raise the level in the 1800s, the river was much shallower within the city most of the time, and consisted of a small channel of continuous flow bordered by sandy banks (depicted in many illustrations of the period). Today the depth is tightly controlled and the entire width of the river between the built-up banks on either side is normally filled with water. The average flow of the river is very low, only a few cubic metres per second, but much higher flows are possible during periods of heavy runoff. Special reservoirs upstream help to maintain a constant level for the river through the city, but during periods of extreme runoff significant increases in river level may occur.
A very severe period of high water in January 1910 produced extensive flooding throughout the city. The Seine again rose to threatening levels in 1924, 1955, 1982 and 1999–2000. After a first-level flood alert in 2003, about 100,000 works of art were moved out of Paris, the largest relocation of art since World War II. Much of the art in Paris is kept in underground storage rooms that would be flooded. A 2002 report by the French government stated the worst-case Seine flood scenario would cost 10 billion euros and cut telephone service for a million Parisians, leaving 200,000 without electricity and 100,000 without