Ebrahim Borooshke; Mahmood Arabkhedri
Abstract
Soil erosion and sediment transport is an important issue in many Iranian watersheds. Watershed planning without accurate estimates of erosion and sediment yield with appropriate models is not possible. The objective of this study was evaluating of two common empirical models of MPSIAC and EPM. First, ...
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Soil erosion and sediment transport is an important issue in many Iranian watersheds. Watershed planning without accurate estimates of erosion and sediment yield with appropriate models is not possible. The objective of this study was evaluating of two common empirical models of MPSIAC and EPM. First, 10 small watersheds were selected in Western Azerbaijan Province, with several consecutive check dams on their streams implemented under watershed management projects. No flow over the last downstream check dam was considered as the main criterion in each selected basin. In addition to the direct measurement of sediment deposited behind the dams, sediment yield of watersheds were estimated using the models. Comparison of means using (Mann-Whithney) did not show any significant difference at 0.05 percent level between measured and estimated data. At final step, both models were tested by MAE and MBE statistics. The MPSIAC showed better performance than EPM with MAE=1.34 and MBE =-0.12.
Abdolali Adelpour; Majid Soufi
Abstract
Erosion and sedimentation study and design of the distance between spreading channels are basic requirement in flood water spreading projects. Different environmental parameters including topography and slope, soil texture, vegetation cover and flow resistance affect the hydraulic characteristics of ...
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Erosion and sedimentation study and design of the distance between spreading channels are basic requirement in flood water spreading projects. Different environmental parameters including topography and slope, soil texture, vegetation cover and flow resistance affect the hydraulic characteristics of the flood water spreading area. So it isnecessary to investigate the effect of environmental parameters according to natural conditions and simulation of overland flow. This study was done in the Gareh Bygone plain, in the south of Fasa city. An open hydraulic flume with 120 m length, 0.4 m width and 0.25 depth was used to simulate concentrated overland flow with 0.1 mdepth. Three experiments were examined and for each experiment, discharge flow and mean flow depth were measured directly and other parameters such as mean velocity and shear stress were calculated. Erosion or sedimentation depths were calculated by comparing flume bed elevations in the cross sections with one meter intervals. Results of this study show that erosion and sedimentation phenomena were changed with theincrease or the decrease in trends of shear stress along the flume and shear stress parameter were also changed with bed slope and roughness coefficient and became maximum at 75 m from the top end of the flume. On the other hand, according to the bed elevations of cross sections in two steps maximum erosion depth occurred at 75 mfrom the start of the flume which was confirmed with maximum shear stress. So, we can conclude that channel erosion threshold was established in 75 m from the top end of the flume and it can be considered as channel spreading distance.
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.
