The Garang River with a catchment area of 204 km² originates from Mt. Ungaran (el. 2,050 m) and flows through Semarang City finally pouring into the Java Sea. There exists a large-scale water intake named the Simongan Weir about 5.3 km upstream from the river mouth, and the river channel below the Weir changes its name to West Floodway from the Garang River.

The River is one important water sources for Semarang City. The sustainable water supply from the river is, however, hardly secured due to the extremely low flow discharge during the dry season. As a result, Semarang City and its vicinities currently suffer from chronic and severe shortage of the municipal water supply. Additionally there is the incidence of flood is another major problem.

Several projects and plan has been implemented on the river in order to cope with all those problems. Unfortunately legal reforms made for the management of rivers has being preventing the implementation of those projects.A new study was Issued by the government of Indonesia with a loan by JBIC to achieve the following objectives:

• To mitigate flood and inundation damages along the West Floodway/Garang River, to develop water resources for municipal and industrial water in Semarang and to improve the drainage system in the central area of Semarang City,
• To improve the environmental conditions along the river and the urban area, and
• To upgrade the living conditions of inhabitants in the project area.