Also, the dam cannot protect against some of the large tributaries downstream, including the Xiang, Zishui, Yuanshui, Lishui, Hanshui, and the Gan. In 1998, a flood in the same area caused billions of dollars in damage; of farm land were flooded. The flood affected more than 2.3 million people, killing 1,526. In early August 2009, the largest flood in five years passed through the dam site. The dam limited the water flow to less than per second, raising the upstream water level from on August 1, 2009, to on August 8, 2009. A full of flood water was captured and the river flow was cut by as much as per second. The dam discharges its reservoir during the dry season between December and March every year. This increases the flow rate of the river downstream, and provides fresh water for agricultural and industrial usage. It also improves shipping conditions. The water level upstream drops from , preparing for the rainy season. The water also powers the Gezhouba Dam downstream. Since the filling of the reservoir in 2003, the Three Gorges Dam has supplied an extra of fresh water to downstream cities and farms during the dry season. During the 2010 South China floods in July, inflows at the Three Gorges Dam reached a peak of , exceeding the peak during the 1998 Yangtze River Floods. The dam's reservoir rose nearly in 24 hours and reduced the outflow to in discharges downstream, effectively alleviating serious impacts on the middle and lower river. The installation of ship locks is intended to increase river shipping from ten million to 100 million tonnes annually, as a result transportation costs will be cut between 30 and 37%. Shipping will become safer, since the gorges are notoriously dangerous to navigate. Ships with much deeper draft will be able to navigate upstream from Shanghai all the way to Chongqing. It is expected that shipping to Chongqing will increase fivefold. There are two series of ship locks installed near the dam (). Each of them is made up of five stages, with transit time at around four hours. Maximum vessel size is 10,000 tons. The locks are 280 m long, 35 m wide, and 5 m deep (918 × 114 × 16.4 ft). That is longer than those on the St Lawrence Seaway, but half as deep. Before the dam was constructed, the maximum freight capacity at the Three Gorges site was 18.0 million tonnes per year.