by Harrini Mutiara Hapsari Wahyu (Thesis M.Sc Unesco-IHE, Delft, Netherland, 2016) supervised by by Prof. Dr. Charlotte de Fraiture, M. Sc., Prof. Dr. Robiyanto H. Susanto, M. Agr. Sc., and Dr. F .X. Suryadi, M. Sc
Urban flooding oftentimes staggers the livelihood in an urban area. This kind of occurrence most likely happens in the lowland urban area. The consequences and the subsequent long term drawbacks of urban flooding sometimes lead to the catastrophic destruction of the existing urban drainage system. Therefore, the existing urban drainage system should be improved in order to tackle the upcoming urban flooding events, which are more than likely becoming more devastating than that in the previous years. The existing urban drainage systems in most countries predominantly use manmade systems. Therefore, those systems need to be upgraded because their capacity to accommodate water has been decreasing gradually over a number of years. In general, urban drainage systems collect water from precipitation and surface runoff, as well as being affected by tidal intrusion from the sea.
The research location is in Palembang City, which is located in the Southern part of Sumatra Island, Indonesia. This capital city of South Sumatra Province has a total area of 40,055 Ha and approximately 30% of the urban part is a lowland area. Palembang is divided by Musi River into two large areas; Seberang Ulu and Seberang Ilir. The case study of this research will be held in Silaberanti, which is located in the Ulu part of Palembang. Palembang has 20 sub catchments, and 17 systems that feed into the Musi River. Aur Sub Catchment is one of the 20 sub catchments of Palembang and it is located in Silaberanti. Therefore, the main study area for this research is in the Aur Sub Catchment which has a total area of 454 Ha. The main objective of this research is to improve the current drainage system in order to achieve the optimal design for urban drainage arrangement. The improvement is essential in order to tackle the problem of urban flooding which is annually happening in this area.
This research was developed using Duflow (Dutch Flow) Modelling Studio 3.8.3 in collaboration with ArcGIS 10.1. Duflow Modelling Studio aims to schematize the drainage system and the purpose of ArcGIS 10.1 is to analyse the spatial and topographical condition of the research area. The existing condition and extreme condition of the drainage system will be established using the Duflow Modelling Studio.
As a result, there are three development scenarios established by Duflow Modelling Studio in order to improve the drainage system in the research area. The first scenario is the current and extreme condition in the study area. Current condition is represented by rainfall and tidal fluctuation during wet season in 2015. Based on the results from the modelling analysis, the maximum level of flooding during the existing condition is 0.30 m 0.80 m.
The second scenario is the extreme condition, which is represented by the extreme rainfall with the return period of 25 years and 50 years with the effect of the highest tidal fluctuation. On the other hand, the maximum water level during the extreme flooding event with a return period of rainfall of 25 years is approximately 0.40 m 0.85 m and during a return period of 50 years is around 0.42 m 0.86 m.
The third scenario is the improvement possibilities of the existing drainage system. There are three different types of improvements and modifications for the third scenario which are: canal dredging, canal dike/embankment, a pump installation, and a flap gate installation. The improvements are mainly focused in areas which have a high risk of flooding, which are started from NOD27 l (Section 18) to NOD35 (Section27) from the Aur River schematization. Each of improvement possibilities gives different results.
Alier i m dredging. the inundation depth reduced to approximately 0.1 m 0.2 m. initially it was 0.4 m 0.8. but ailer the dredging it was decreased around 0.2 m – 0.7 m. However, the inundation is still happening.
The canal dike constructions give a significant impact for the flooding in research ‘ me. For a 50 cm dike construction, the surface level increased, and the inundation level decreased. However, the height of freeboard is relatively small and some sections in the flood risk area are still inundated by 0.1 m to 0.3 m. 0n the other hand. a l m dike construction gives a better result than the construction of a 50 cm dike. The surface level was up to 2.2 m+MSL, initially 1.2 m+MSL. The result shows that the height of freeboard is around 0.5 m, which is comparatively good for anticipating the extreme flooding.
A pump installation shows an important impact for preventing the flooding in Aur River as well. The installation of a pump with capacity 12 m3/s in the downstream part combined with l m dike in the flood risk sections of the scheme are able to reduce the water level during the extreme condition. The pump starts to work when the water level is exceeding the predicted water level limit, and will be turned off when the water level in the Aur River is back to normal. The simulation gives a result where there is no inundation after the pump is installed in the system.
A flap gate also gives a desirable result for preventing the flooding in Silaberanti. An installed flap gate is working based on the water level from both Musi River and Aur River. When the water level in Aur River is higher than the desirable limit, the flap gate will Open and let the water flow to Musi River. As the simulation result, there are no occurrences of flooding in Aur River.
In conclusion, based on three different scenario analyses, the most feasible, suitable, effective, and efficient alternative for overcoming the flooding in Silaberanti is a flap gate installation combined with dike construction in the flood risk sections of the river.Because it is working automatically depending on the water level in the River, it also does not need an extensive labours for the operational purposes, and it is very effective in reducing the flooding in Aur River.
In addition, in spite of the technical approaches, the practical approaches also need to be taken into consideration in the activities of improving the urban drainage system in Silaberanti. Some practical approaches are included in these practical approaches, such as implementing the development concept of “Living with Water ” for the further urban expansion as well as revising the government policy. These technical and practical approaches need to be combined in order to outcome the optimal result for solving the problem of flooding in area of Silaberanti.
Keywords: DUFLOW, drainage system, flood modelling, GIS, inundation, urban drainage, urban flooding