Mitra Tanhapour; Mohammad Ebrahim Banihabib
Abstract
Debris flow is one of the natural hazards that threats people's lives in the mountainous populated areas. Thus, it is necessary to determine the rainfall thresholds for debris flow occurrence in order to develop an effective forecasting system. In this study, the empirical thresholds of rainfall for ...
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Debris flow is one of the natural hazards that threats people's lives in the mountainous populated areas. Thus, it is necessary to determine the rainfall thresholds for debris flow occurrence in order to develop an effective forecasting system. In this study, the empirical thresholds of rainfall for the occurrence of debris flow by Hirano method were assessed in a part of Alborz mountainous basins including Gorganrood, Navrood, Neka and Babolrood. For this purpose, the rainfall hyetographs of recording rain gauges were used from the period of 1983-2004. Then, the intensity-duration rainfall thresholds (I-D threshold) for selected basins were estimated and compared with previous studies from the local, regional and global scale. The examination of rainfall thresholds for the initiation of debris flow showed that the rainfall of more than 27.2 and 14.8 mm, respectively, in the Navrood and Gorganrood watersheds and rainfall more than 37.84 and 66.12 mm, respectively, in the Babolrood and Neka basins are able to trigger debris flow during their concentration time. Comparison of the I-D threshold of this study with the results of previous studies showed I-D threshold of the studied basins generally are lower than the thresholds of local and regional but higher than global thresholds. In other words, there are some areas in the world that need smaller rainfalls for initiation debris flow in comparison to the study area. The difference among threshold of debris flow occurrence in the world’s basins comes from their variety in climatic, geographical, physiographic and geological factors.
Seyedeh Maryam Alibakhshi; Mohammad Mahdavi; Shahram Khalighi Sikaroudi
Volume 2, Issue 2 , July 2010, , Pages 102-110
Abstract
Approximation of precipitation and design of a rain-gauge system with minimum initial cost and robustness against measurement uncertainties requires finding the relationship between various stations equipped with udometers .On the other hand, in areas where the issues of erosion and sediment exist, it ...
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Approximation of precipitation and design of a rain-gauge system with minimum initial cost and robustness against measurement uncertainties requires finding the relationship between various stations equipped with udometers .On the other hand, in areas where the issues of erosion and sediment exist, it seems necessary to know the amount of rainfall. Among the possible solutions, increasing the number of rain gauges can be adopted which is expensive. In the present study, rainfall data of 16 base stations by Ministry of Power recording precipitation data of Tehran Province on a common date (1622 rainfalls) were extracted. In each measurement, a station was chosen as base, the rainfalls of other stations were ignored, so the rainfall of each of them were reconstructed according to base stations, which were finally compared with observed rainfalls. Then, the curve of reconstructed and observed rainfalls was transformed into a dimensionless form, and rainfall percentage in the three quarterlies and the surface under each curve were calculated. Eventually by figuring out the error percentage of them, the frequency of error percentage in anticipating the rainfall amount and the three quarterlies for both curves were calculated. In order to determine the ratio of sensitivity of the model, distance index with statistical estimation of percentage of variation coefficient was used. Results demonstrated that there is no elevation effect within the 900 to 1800 m from sea level, but, there is a jump in the amount of error that this situation reduces gradually up to 2000 m height.
