Rainfall Analysis Planning to Calculate Runoff Water Discharge at PT. Triary Regency of North Musirawas, Sumatera Selatan

Abstract

PT. Triaryani is a coal mining company with open pit mining method which located in North Musirawas Regency, South Sumatra Province. In the management of water that goes into the mine is done the manufacture of sump contained in the eagle pit. Sump has a function as a place or pond of water reservoirs that enter to the mine, the water will then be pumped to the settling pond (KPL) will then be neutralized by the distribution of lime and alum 1:4 and flowed to the river. The purpose of this study is to find out the discharge of runoff water and make a sump design in 2021 that can accommodate the discharge of runoff water with maximum rainfall. In the manufacture of sump design is taken into account the discharge of runoff water that will enter so that rainfall data is needed in the area. Rainfall data used from 2011 to 2020 which can beobtained from BMKG South Sumatra rainfall data and rainfall data measured by Triaryani’s survey team. The rainfall data will be calculated by dispersion of rainfall data. Dispersion is done to know the distribution of rainfall data to be analyzed, so that the analysis method used is the most appropriate method. Determination of rainfall plan in this study was conducted by rainfall analysis by E.J. Gumbel method based on dispersion results. Slope factors and compactness of the area make rainwater that falls to the surface is not infiltrated so that the flow of runoff water.  In order to avoid flooding at the mining site, in the manufacture of sump required calculation of runoff water discharge to be able to know the water that enters the pit.From the calculation obtained the value of the coefficient of runoff of the region is 0.9. Rainfall intensity value is 15,285 x 10^-7 m/s with catchment area 538,600 m². Runoff water discharge obtaining is 64,016.88 m³/ day, so the sump plan made to be able to accommodate the discharge of runoff water is with a depth of 6 m, base length of 97.3 m and surface length of 109.3 m. Sump plan can accommodate the discharge of runoff water with maximum rainfall per day without pumping.