by Citra Girsang: (Thesis M.Sc Unesco-IHE, Delft, Netherland, 2015) supervised by Prof. Dr. Charlotte de F raiture, M.Sc (UNESCO-ME, Delft, the Netherlands), Prof. Dr. 1r. Robiyanto H. Susanto M.Agr.Sc (Sriwijaya University. Indonesia), and Dr. F.X. Suryadi, MSc (UNESCO-1H8, Delft, the Netherlands)
Palembang city as one of the big cities in Indonesia frequently suffer from flood problem, include flood problem in Buah watershed. Flooding in Buah watershed is affected by natural factors, such as: the characteristic of the river that has small capacity, arise oftidal fluctuation hold the river flow in downstream and topography condition that relatively flat thus some parts of Buah watershed is a flood plain. In addition, the flood problem also affected by non-natural factors such as rapid population growth of urbanization and land use change directly cause a reduction in the availability of green open space as catchment areas. Buah watershed with 7.5 km length has many meanders and has permanently plastered along the river. Furthermore, Buah watershed with an area of 850 ha in general is a residential area, industrial and swamps.
Hence, the research that has three objectives, specifically to evaluate the existing condition of urban drainage system in Buah watershed area; to identify the impact of tidal fluctuation, the intensity of rainfall, and accumulation of solid waste and sedimentation to the urban drainage management; and to recommend an appropriate improvement to the urban drainage system in Buah watershed area. To achieve the research objectives, the analysis applied on this research are spatial analysis through Geo Information System (ArcGIS) and hydrological modelling through DUF LOW Modelling Studio (DMS).
On this study, there are some options that proposed to improve the urban drainage by using the Duflow Model System (DMS) software as the modelling to evaluate the appropriate solution to overcome the inundation problem. Initially, we perform the existing condition model which is show the real condition in Buah watershed. In the existing condition model, the inundation occurred for height of flood is about 0.5-0.9m. To find solution on this flood problem, the extreme condition model is proposed on this study. If the extreme condition modelling with the maximum of rainfall with 50 years return period as boundary condition in upstream area and maximum of tidal fluctuation as boundary condition in downstream area can be solved, then the existing condition’s flood problem also can be solve.
In extreme condition circumstances, the depth of the flooding reach up to 1.34.4 m with 24 hours durations. In order to cope the high of flood, there are four scenarios was developed. Firstly, scenario l is improve the urban drainage by changing the Chczy coefficient. This scenario l can reduce the depth of flooding for 0.2-0.3 m from extreme condition model, however the depth of flooding is not decline significantly, the flood still occurred with inundation level up to lm. Secondly, scenario 2 was proposed with building the dikes along the river embankments. The scenario 2 reduce the flood level for 0.3-0.6 m from extreme condition model. The dikes construction is built for 3 km length from urban drainage in the upstream area. Thirdly, scenario 3 is suggested by retention pond construction in upstream area. Construction the retention pond decrease the inundation depth for 0.2-0.5 m from extreme condition model. The wide of retention pond is about 2.5 Ha with depth of 3 m from surface level. Finally, propose the scenario 4 with normalization the canals by dredging the canals for about 0.5-l m from existing floor level. This scenario give significant impact in reducing the flooding for about 0.9-1.3 m. After running this scenario 4, there is no flooding anymore in the study area.
In addition, since the inundation is occurred in upstream and middlestream of Buah watershed, the tidal fluctuation in downstream do not give significant impact in flood occurrence because of the difference of topography. The flooding is occurred because of lack capacity due to sedimentation and insufficient dimension of canals when high intense of rainfall occurred. Based on the Duflow modelling result, the scenario 4 with normalization canals by dredging canals as an appropriate option to improve the urban drainage management and flood control in Buah watershed, Palembang City. Hence, it is recommended that it is needed community awareness particularly who are living around the watershed in order to participate in efforts to maintain the urban drainage system by do not throw solid waste or do not build illegal house along the river embankments thus the urban drainage will be able function properly.
Keywords: Urban Drainage, Flood Protection, Dujlow, Buah Watershed