Reliability of rainfall intensity prediction method for mine dewatering design in tropical region
Convective rainfall type which is very common in most mines in tropical region is characterized by its high intensity in short duration. For mine dewatering design purposes it is necessary to analyze the extreme rainfall intensity for a certain return per
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Abstract. Convective rainfall type which is very common in most mines in tropical region is characterized by its high intensity in short duration. For mine dewatering design purposes it is necessary to analyze the extreme rainfall intensity for a certain return period. Extreme value type I probability distribution is the most common used method for storm rainfall analysis. In this paper, the 2-year return period rainfall intensities are calculated for various data series and time periods. The results are compared to the observed rainfall data to see whether the prediction is considerably in line with the actual rainfalL
Background Rainfall is derived from atmospheric water. The condensation is generated by dynarnic or adiabatic cooling due to the vertical transport of air masses. According to the conditions that generate vertical air motion precipitation may be classified into three categories, e.g. convective, orographic and cyclonic. Convective rainfall is typical of the tropics and characterized by high intensity rainfall in a short duration. The heated air expands with a resultant reduction in weight, increasing quantities of water vapor are taken up, the warm moisture-laden air becomes unstable and vertical currents are developed. Dynamic or adiabatic cooling takes place, causing condensation and precipitation. Orographical precipitation results from the mechanicallifting of moist horizontal air currents over natural barriers such as mountain ranges. Both rainfall types commonly occur in tropical regions like Indonesia.
B. J. Merkel et al. (eds.), Uranium in the Aquatic Environment © Springer-Verlag Berlin Heidelberg 2002
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Rudy Sayoga Gautama
With a rainfall rate of 2000 mm to 5000 mm per annum, rainwater is the main water problern in almost all open pit mines in tropical regions like Indonesia. The tropic climate of Indonesia is influenced by the monsoon which divides the yearly season into dry and rainy seasons. At most mine sites the rainfall type is convective and in some mines orographic. In a mining area the high intensity of convective rainfall will significantly reduce the effective working hours of mining operation. Certain rainfall intensity will cause muddy conditions, particularly in mining fronts, and the slippery haul roads. Due to operational and safety reasons the operation in such conditions is usually delayed. Data ofNovember 2001 in Bukit Asam Coal Mining Area shows that total delay time due to rainfall and slippery haul road condition is 184.75 hours and it is 25.7% ofthe scheduled monthly working time. To minimize the impact of rainwater on the mining operation it is necessary to define the appropriate design parameter for mine dewatering facilities. The main parameter is a predictive rainfall intensity with a certain level of probability of occurrence which accounts the hydrologic risk of dewatering facilities.
Storm Rainfall Analysis Rainfall is considered as a random event and it varies geographically, temporally and seasonally. In designing the mine dewatering facilities it i
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