by Nur Ariyanto (Thesis M.Sc Unesco-IHE, Delft, Netherland, 2016 ); supervised by Charlotte de Fraiture, Robiyanto H. Susanto, and F.X. Suryadi
Main objective of this study is to find out the most suitable scenarios that can be applied to improve the water management system in the study area. The specific objectives are to identify the existing condition in the study area, to propose precise improvements of the drainage system, and to propose an appropriate flood management system in connection with a reliable agricultural water supply.
In order to achieve the research objectives, several measures have been considered. First, identifying the existing condition was accomplished by field observation and Duflow Modelling Studio (DMS) with a boundary condition of the maximum rainfall occurrence, which is 169 mm/ day for 24 hours and tidal boundary conditions were assumed to be increasing by 30 cm. Second, to check the required drainage improvement due to extreme rainfall which resulted from the Gumbel Distribution with 100 years rainfall return period and tidal boundary condition as the downstream boundary. In this study 4 different scenarios have been developed: Scenario 1 maintaining the canals; Scenario 2 widening the canals; Scenario 3 construction of dikes; and Scenario 4 construction of long term storages and gates. The last scenario is propose to provide not only flood management but agricultural services.
The results show that the existing drainages infrastructures lack maintenance, they are overgrown by grass weed. During a dry season this study area experiences drought due to poor supply water from the Primary Canal. In contrast during the rainy season, section of the primary canal and other portions of the drainage system are frequently inundated. In other words, the existing drainage is insufficient to accommodate runoff from rainfall and tidal Huctuations from the Kremasan River.
Based on DMS simulation, the enhancement of drainage system, in Scenario I by maintaining the existing canals will not significantly to reduce flooding. This scenario can only reduce the duration of flooding. The Scenario 2 is performed by widening the canal as wide as 2 m. The second scenario only result in a reduction the floods while the duration of flooding is almost the same with the Scenario 1. While, the Scenario 3 requires the construction of dikes alongside Primary Canal 1, Primary Canal 2, and Secondary Canal 1 as high as 0.01 m+RL to 0.60 m+RL. As a result the third scenario can overcome the flooding in all sections. In Scenario 4, construction of long storage that connect Primary Canal 1, Primary Canal 2, and Primary Canal 3 equipped with flap gate and stoplog gate can handle flooding in Secondary Canals 1, while in Primary Canals l and Primary Canals 2 this scenario can reduce flooding. In terms of duration, this scenario can reduce duration up to 9 hours in some sections. In fact, by construction of long storage although flooding still occurs in study area, this storages can hold the water from flooding, so that it can be utilized for agricultural purposes. Moreover, in the dry season, during the highest high tides, which occurs once every two weeks, this long storages can be refilled and can supply water for secondary canal during low tides.
Based on the evaluation it can be concluded that the Scenario 3 is an appropriate inundate solution to handle the flooding in this study area. However, by consrdermg possible future agriculture development the Scenario 4 can also be considered.
keywords: Duflow, KTM Rambutan-Parit, and Flooding