In Rotterdam, buildings, such as garages, are constructed as emergency reservoirs in case of sewage overflow. Fountains, gardens and basketball courts are built to act as retention ponds. Rotterdam has also constructed the Maeslantkering, a giant floodgate designed as swinging arms that open and close in order to regulate water flow. The arms of the floodgate also act as seawall, protecting the city from tides or flooding. All these installations work to guide flooding and use the water for the advantage of the city. Moreover, the projects are designed to help poor communities and encourage economic growth. For instance, increased investment in poor communities catalyzes business growth and creates jobs. Local businesses use their expertise to sell environmental solutions all over the world, increasing GDP through exports. Meanwhile, the gate catalyzes trade by protecting the port, which is a hub of steel and petrochemical trade.