ANALYSIS OF THE INFLUENCE OF RAIN CENTROID POSITION ON LEAD TIME IN THE UPSTREAM CITARUM RIVER

• Main Author: Ayuningsi Ode Asri, Aristi
• Format: Theses
• Language: Indonesia
• Subjects: Teknik sipil
• Online Access: https://digilib.itb.ac.id/gdl/view/75007
• Institution: Institut Teknologi Bandung

Flood disasters are Indonesia's most dominating natural disaster trend yearly. The high incidence of flooding in West Java is caused by the morphological conditions of the area in the form of a basin in the Upper Citarum area. One of the areas most affected by flooding in Upper Citarum is Majalaya. Floods in Majalaya generally occur quickly and experience a rapid rise in water level. So efforts are needed to reduce the impact of flooding by predicting the time from the start of rain or issuing a warning until the water level in the river rises, called the lead time. The determination of the lead time is influenced by several aspects, namely the decision to start the issue warning, the peak discharge, the characteristics of the river, and even the position of the main point. This study examines the effect of the distance from the midpoint of the rain to the observation point of discharge and water level and whether it affects lead time. Utilizing the GSMaP satellite rainfall data source, corrected water level, and discharge data from the Jasa Tirta Corporation 2's gauge, lead times can be determined in the Majalaya and Sapan watersheds. Furthermore, whether the centroid affects the lead time in the two watersheds can be seen. The rainfall centroid is extracted from the raster data, which is multiplied by the corrected rainfall to obtain the centroid point of the rain. The distance from the centroid point to the AWLR point is calculated using the Euclidean distance formula—70 representative data were used to determine the lead time that occurred in Majalaya and Sapan. The results show that the lead time in Majalaya is 1 hour, with a 76% probability of occurrence. Most events in Majalaya were lead times of 1 hour and 2 hours. However, do not dismiss the possibility of the risk of waiting time of less than 1 hour occurring as much as 24%. The waiting time given to evacuate in Sapan is longer, more than 4 hours, with a probability of occurrence of 86%. In contrast, the waiting time for peak discharge events from the highest rainfall occurs between 5 hours and 6 hours. The risk of a waiting time of less than 4 hours is 14%. The results of the rain centroid show that there is no effect on the lead time. However, it was found that the rain centroid is in the middle of the Majalaya and Sapan watersheds and forms an abscissa. Thus, rain observations from any point and at any time are always in the middle. In the Majalaya region, at a distance of 2 km from the central point of the DAS, there were 31 rain incidents. Another thing is shown in the Sapan watershed, where the total number of rain events is 34. The farther from the central point of the watershed, the less chance of rain or even none. Spatially, centroid does not affect lead time. This is due to the random spatial distribution of rainfall. Then a temporal analysis is carried out by determining the rain distribution. However, the results show that temporally, the centroid does not affect lead time. The following analysis is to determine the time to peak from the time range from the start to the end of the rain. This study considers the time to peak linear with the centroid distance. The different shape of the watershed shows that the centroid points of the rainfall will be equally close to the center of the watershed and form an abscissa line according to the shape of the watershed.