Variability of Discharge Inflow in Wonorejo Reservoir, Indonesia

Discharge variability such as frequency and magnitude at certain seasons has the main control on the hydrological behavior of the river. This means a better understanding of discharge variability for reservoir inflow it can be used to manage water reservoir manajement more effectively during the wet year we can use more water, and during the dry season water saving must be done. This flow discharge variation was investigated using data for 18 years from 2003 to 2020 using data on the daily inflow gate of the Wonorejo Reservoir. This study was used to examine the Standardized Precipitation Index (SPI) and statistical methods in the form of average annual discharge, standard deviation (SD), and coefficient of variation (CV) were used to determine the relationship between rain and discharge that occurred. The results of this study show the variability of the discharge for wet, normal and dry years, as well as the distribution of, and changes in the stream flow record. This study is very valuable in order to know the trend of seasonal discharge that occurs, the estimated highest and lowest discharge, as well as the annual discharge cycle in the context of water resources management. Thus, the inflow discharge of the Wonorejo Reservoir from January 2003 to December 2020 shows that each time series follows a normal distribution with a probability percentage of a wet year and a dry year of 41% while a normal year is 11%.