For convenience in managing the city's extensive network of interceptor and collector sewers, DWU has divided the system into a number of primary sewer basins based on the drainage pattern for the sewers within the basin. There are 12 primary basins. Ten of the basins transport flow to Dallas treatment plants. These basins are (alphabetically) the Elam Creek, East Bank, Five Mile Creek, Hickory Creek, Prairie Creek, South Dallas, Warren Avenue, West Bank and White Rock Creek Basins. Each basin is named for, and discharges flow into, the major interceptor sewer line traversing the area. The other two primary basins transport flow to other regional sewer providers. These basins, the TRA and Garland basins, are named after the regional provider. The primary basins are further divided into smaller drainage basins, termed sewersheds. 48 of the sewersheds are tributary to Dallas wastewater treatment plants, three of the sewersheds are tributary to the Trinity River Authority (TRA) system, and one is tributary to the Garland system. The DWU Wastewater Collection System is over long and includes 15 lift stations. Pipe sizes in the system range from 4" to 120" inches.