By Andi Irawan – (Thesis M.Si Sriwijaya University, 2012), Supervised by Prof. Bart Schultz, PhD, MSc; Prof. Ir. Robiyanto H. Susanto, PhD, M.Agr.Sc; F.X. Suryadi, PhD, MSc.

Tanjungpinang City has four sub-districts and eighteen villages with a total area of 240 km2 consisting of 132 km2 upland and 108 km2 sea. The City, which has a slogan “city of traditional poetry”, had in 2010 a population of 188,000 inhabitants. Population growth rate from 2000 to 2010 was 2.79%. It is relatively large. This is caused by the fact that Tanjungpinang City has been established as the Capital of Riau Islands Province. To avoid bigger problems in the future, the Government of Riau Islands Province has assigned a new area as the seat of the central government of Riau Islands Province. Besides that, a problem that often happens is flooding, especially during heavy rains because of rapid development of the city and land use change. There are several locations that can be flooded during heavy rains and high tides. To indentify and analyse the existing condition in order to create the best solution which can be used to overcome the problem, simulation by using Duflow Modelling Studio (DMS) and Geographical Information System (GIS) have been done.

Geographically, Tanjungpinang City is also very sensitive in the changing conditions of land where the land is hilly and is a coastal town which is strongly influenced by tides. The need for land for housing and business premises has changed some catchment areas into residential and business centres. Some housing built by the developers do not have good planning such as the channel waste water from homes, shelters trash and green spaces. The hills which were once covered with trees, have now been deforested and turned into residential and business centres. It also happens in the swamp area which was as water storage reservoir.

Based on the cause of flooding where water was coming from, there are two types of flooding, namely runoff flooding and tidal flooding. Related to condition in Tanjungpinang City, three types of flooded areas have been identified with different cause of flooding. Those areas are regularly flooded because of heavy rain, heavy rain and high tides, and high tides. Those are Rawa Sari area, Pemuda area and Yudowinangun area.

Simulating by DMS presented that some locations in Rawa Sari area were flooded up to 18 cm above ground surface level when heavy rain occurred. According to analysis, flooding occurred because of insufficient capacity of drainage, not only the dimension of drainage but also the performance of drainage. Meanwhile, flooding in Pemuda area occurred up to 49 cm when heavy rain and high tides were coming. In this case, the cause of flooding was similar to the previous area but high tide strongly influenced. The last area is Yudowinangun area where tidal flooding firstly occurred about 4 cm in some locations with even no rainfall. It would be 34 cm when heavy rain occurred.

The recommended solution is widening, dredging, and maintenance of drainage. For some locations in Pemuda area and Yudowinangun area, retention ponds need to be established because the free space is available and gate equipped with a pump should also be applied in order to control water coming from sea.

Keywords: Urban Drainage, Flooding, Flood Protection, Duflow, GIS.