Rachmad Jayadi

Restoration of peat dome in ex-Mega rice project area in Central Kalimantan

Restoration has been carried out on several tropical peatland water systems in Indonesia. One of them held at ex-Mega Rice Project Area (EMRP) of a million hectare of peatland in block A, Sei Ahas Village, Mentangai, Kapuas District, Central Kalimantan. The method was used to create a canal blocking in several locations which was expected to increase water table level and to repair degraded peatland ecosystems. In this recent research, two cases of blocking in canal D and E had been compared to canal C condition without blocking of water table in upstream blocking and peatland ecosystems. Based on 3 years field observations in restoration process and secondary data in peatland water system by canal blocking constructing, there was finding obtained by the presence of the block on canal E, water table in upstream canal can be maintained at time of rainy season and dry season/ Therefore, the peatland might be inundated. In canal C with no blocking, the level was 0.2 m above the bottom of the canal at the end...

Integrated Simulation of Spillway and Diversion Structure in Flood Risk Assessment of Upper Solo River

Wonogiri Reservoir is a multi-purpose hydraulic structure that is used for water supply service and flood control in the watershed area of Upper Solo River. Inflow of the Wonogiri Reservoir comes from 10 rivers in the watershed’s catchment area. As for the purpose of reservoir’s sediment controller, a new spillway is constructed; and also closure dike is being built, which influenced the change on reservoir storage characteristic, and then means that a new reservoir operation guideline is necessary. Therefore, study on flood routing on the watershed of Upper Solo River at the new condition of the reservoir operation is needed. The analysis was conducted to acquire detailed information on flood characteristics of Wonogiri Reservoir and Upper Solo River started from the downstream of the reservoir until the downstream control point in the Jurug Water Level Recorder including the flood discharge and the maximum water level. The analysis procedure was performed by four components, which are flood forecasting, reservoir flood routing, rainfall-runoff lateral inflow, and hydraulic channel routing. The analysis result was integrated into a software package which was arranged by using the Microsoft Visual Studio Express 2012, Microsoft Access, and HEC-RAS. With the support of the software, it was expected that the decision making in the spillway operational is more quickly and more accurate (rapid assessment) in order to improve the flood control performance in the area of Upper Solo River.

Urban Flood Control in Sringin Catchment, Semarang City, Central Java Province, Indonesia

Sringin is the lowland area located in Semarang city which has been vulnerable to rob flooding from the Java Sea along with flood triggered by the intense amount of rainfall. The case study will further discuss the hydrological analysis, transformation of rational method into flow hydrograph with the design rainfall of 25-year return period, and unsteady flow analysis by HEC-RAS 5.0.3 under existing condition and design condition. The result shows that the design rainfall of 25-year return period measures 173 mm in vertical length and data collected from the office of public work, Semarang city can be used to implement the design scenario with normalization of drainage system and the increase of levee with the freeboard up to 0.75 m is proved to be the solution to the flood inundation in that flood-prone area while the flood under existing condition has caused excessive discharge at downstream up to 9 hours.

Impact of Sedimentation Counter Measure on the Performance of Flood Control: A Case Study of Wonogiri Reservoir

The Wonogiri Reservoir with 1.343 km2 catchment area has a major problem of sedimentation. To overcome this issue, a new spillway has been built and closure dike is being constructed to localize sediment inflow from the Keduang watershed. Study on the effect of the closure and overflow dike on the reservoir operation in flood period is necessary to evaluate the performance of flood control related to the flood risk in the downstream area of the reservoir. For this purpose, the reservoir routing simulation model was developed under two condition, namely old condition and new condition with the new spillway and closure dike. The reservoir routing simulation was conducted for three inflow hydrographs of 60 and 500 years return period, and probable maximum flood (PMF). The results show that the presence of closure dike causes the peak outflow discharge increases to 1.45%, 75.18% and 56.28% for inflow hydrograph of 60 years, 500 years return period and PMF, respectively. Furthermore, the maximum water level also increases by 0.3 m, 1.9 m and 0.9 m for those three new design floods respectively. In order to reduce the dam overtopping failure chance of the 500 years return period flood, it is recommended to operate full opening of the new spillway gate when the water level reaches elevation +135.6 m MSL.

Rain Behaviour at Mt. Merapi Area as Observed by XMPR and ARR

Short duration rainfall information has now become one of many important aspects to support the development of warning criteria for disaster mitigation. Similar importance is also found in the development of warning criteria against the lahar flow disaster at Mt. Merapi area. The rainfall information obtained from the radar observation has also become a new challenge for the last decade in line with the rapid growth of information and communication technology. However, the accuracy of its estimation needs to be evaluated by considering the correlation between radar rainfall and rain gauge rainfall. In case of radar rainfall can be precisely estimated, this information will contribute to generating appropriate warning criteria. This study was carried out as the first attempt to evaluate the rainfall information as performed by the X-Band Multi Parameter Radar (XMPR) that was installed at Mt. Merapi in the mid-August 2015. Several ground rainfall data obtained from Automatic Rainfall Recorder (ARR) have been adopted to analyze the aforesaid radar rainfall information, and estimated errors between the two are presented. Evaluation of the radar estimated error value as a function or range is taken through a Fractional Standard Error (FSE) index that quantifies the differences between ground rainfall measurement (G) and radar rainfall estimation (R), also the G/R ratio characteristics. The result shows there was a poor correlation between radar estimated and rain gauge measured rainfall located over 14 km from radar. Radar bias (M) is suitable for correcting radar rainfall amount, yet inappropriate for fractional values.