By Ningsih, M.Sc. – (Thesis M.Sc. Unesco-IHE, Delft, Netherland, 2014), Supervised by Prof. Charlotte de Fraiture Ph.D., M.Sc., Prof. Dr. Ir. Robiyanto H. Susanto, M.Agr.Sc. and F.X. Suryadi, Ph.D., M.Sc.
Urban drainage system is an important infrastructure in cities especially located in lowland area. The drainage system could be a kind of flood controls therefore it needs to be managed properly in order to secure an area from flooding. The components of urban drainage system may consist of drainage canals (primary, secondary and tertiary), retention ponds, outfall structures (gates), culverts, etc. The drainage system could accommodate all urban water such as rainfall runoff, tide and wastewater. In order to maximize the function of the urban drainage system and consider the environmental impact, nowadays many countries move to better use of natural urban drainage system.
The study location is in Jakabaring development area located in Jakabaring Sub-Basin, Palembang City, South Sumatra Province, Indonesia with area 1,857 ha. Initially Jakabaring area was a swampland which was used to be inundated during high tide. Now most of Jakabaring areas have been reclaimed into commercial land uses such as settlements, housings, sport centre, government offices, etc which may create flooding problem in the area. The main objective of this study is to find a good urban drainage management system in Jakabaring Development Area in order to be free from flooding. Meanwhile the specific objectives are to to analyze the existing urban drainage management system in Jakabaring area, to determine the optimum water level in the drainage canals, to identify the impact of sea level rise, the rainfall intensity, and a large number of wastewater discharge from the human activities in 100 years of return period toward the increase of water level in the drainage canal and the magnitude of flooding area and to propose an appropriate improvement to the urban drainage system in Jakabaring development area.
This study is carried out to propose some alternatives that can be done to overcome flood problem in Jakabaring development area through a technical approach by using DUFLOW Modelling Studio software to estimate water level in the drainage canals and also Geographic Information System (GIS) software to see the magnitude of the inundation area which may occur. The model will be developed in two conditions; existing condition and extreme condition. In the existing condition, the water levels are only influenced by tide and rainfall runoff. Meanwhile, in the extreme condition, the water levels are influenced by tide, rainfall runoff and wastewater discharge which may happen in 100 years of return period.
The maximum water level got from both existing and extreme condition will be overlaid to the topography map of research location to see the inundation may occur. Some scenarios will be developed both in existing and extreme condition to deal with the flooding problem shown in each map of level of flooding in the research location.
In the existing condition, the difference of water level due to tide only and tide together with rainfall in all sections are 0 – 15 cm. Meanwhile, inundation areas in existing condition cover about 245 ha or about 13% of the total area which consists of inundation depth 0 – 0.5 m (186 ha), 0.5 – 1.0 (55 ha), 1.0 – 1.5 (4 ha). To deal with this inundation problem, there are three scenarios which will be developed related to each other as follows:
- Operating the existing urban drainage system;
- Canals normalisation and culvert construction;
- Gate installation in the borderline canal.
Applying those three scenarios could reduce the inundation area to 75 ha or about 4% of the total area.
In the extreme condition, the difference of water level in all sections due to tide only and tide together with rainfall in ranges 0 – 20 cm while due to tide together with rainfall and wastewater discharge the difference is about 0 – 10 cm. Inundation areas in extreme condition cover about 327 ha or about 17.6% of the total area which consists of inundation depth 0 – 0.5 m (147 ha), 0.5 – 1.0 (159 ha), 1.0 – 2.0 (21 ha). To deal with this inundation problem, there are also three scenarios which will be developed related to each other as follows:
- Construction of all scenarios in existing condition;
- Building a new retention pond;
- Pump installation in Propitan Canal.
Applying those three scenarios could reduce the inundation area to 163 ha or about 8.8% of the total area.
Based on the modelling result, all technical approaches done to overcome flooding problem in Jakabaring development area do not give a significant result while they require a lot of money. Therefore, to cope with the flooding problem in Jakabaring development area, it may need other alternative solutions such as social or living with water approach by implementing “Rumah Panggung” as design of settlements and housings, revising the government policy related with the land use change in Jakabaring and also decreasing the population growth rate through encouraging family planning program.