جستجوی مقالات مرتبط با کلیدواژه « معادلات تجربی » در نشریات گروه « آبخیزداری، بیابان، محیط زیست، مرتع »

Roughness coefficient is one of the main factors that lead to energy loss in channels and rivers which have a very important role in water level in cross-sections of rivers. There are several methods that suggested by various researchers for estimating roughness coefficients which are mostly based on experimental tests. In river hydraulic, flow resistance or roughness coefficient is changing because of bed mobility. In this case, a flow resistance formula cannot be used directly without any information about changes of flow resistance coefficient, in different situations of flow and sediment processes. Gol-Gol River of Ilam dam selected for this study. So, results of various empirical methods obtained to find out this coefficient using field survey and characterization of rivers such as cross-sections, soil materials of river bed and banks, then results compared with observed and simulated data of river flow. The HEC-RAS software used to determine the water level in different cross-sections for various discharges and roughness coefficients. Results showed that among various methods, results of Chow method was closer to the observed data, and this method had the lowest mean relative error, so it recommended as the best method to estimate the manning roughness coefficient of this river.

The saturated hydraulic conductivity is one of the most important and widely used geotechnical parameters. This parameter depends on properties of the fluid, pore size distribution, and characteristics of the solid surfaces. Because the latter two are not necessarily constant, the hydraulic conductivity may vary significantly. So far several empirical relationships for estimation of the hydraulic permeability with respect to the type of materials have been presented. In this research seven applicable method including Terzaghi, Kozeny-Carman, Chapuis and Aubertin, modified Navfac, Shahabi et al., Mbonimpa et al. and Chapuis were evaluated. Four samples of sandy soils (R1 to R4) with a rather wide range of particle sizes were prepared and were compacted within the Plexiglas box. After providing the head of 0.5,1 and 1.5 meters; flow discharge and static pressure were measured which result phreatic and iso-potential lines extraction. By applying the results of the model, the accuracy of some common methods used in the estimation of saturated hydraulic conductivity of sandy soils was evaluated. For the samples (R1 to R4), the coefficient of permeability was 0.0051, 0.048, 0.076, and 0.19 cm/s respectively. Due to the limited range of input parameters, the method of Shahabi et al. can be used only for the R4 sample; so this method was discarded from statistical analysis. Comparing the results of laboratory test with common methods shows the methods of Kozeny-Carman and Chapuis and Aubertin were more accurate according to the highest R2 and lowest RE and RMSE. These methods were based on effective parameters and the results of accurate laboratory studies. The method of Mbonimpa et al. (2002) indicates the maximum deviation from observed values which may be due to the sensitivity of this model to void ratio (e). Also the results shows by increasing of void ratio the error of Mbonimpa et al. method increases.

Assistant Professor¡ Soil Conservation and Watershed Management Institute (SCWMRI)¡ Tehran¡ Iran. The saturated hydraulic conductivity is one of the most important and widely used geotechnical parameters. This parameter depends on properties of the fluid¡ pore size distribution¡ and characteristics of the solid surfaces. Because the latter two are not necessarily constant¡ the hydraulic conductivity may vary significantly. So far several empirical relationships for estimation of the hydraulic permeability with respect to the type of materials have been presented. In this research seven applicable method including Terzaghi¡ Kozeny-Carman¡ Chapuis and Aubertin¡ modified Navfac¡ Shahabi et al.¡ Mbonimpa et al. and Chapuis were evaluated. Four samples of sandy soils (R1 to R4) with a rather wide range of particle sizes were prepared and were compacted within the Plexiglas box. After providing the head of 0.5¡1 and 1.5 meters; flow discharge and static pressure were measured which result phreatic and isopotential lines extraction. By applying the results of the model¡ the accuracy of some common methods used in the estimation of saturated hydraulic conductivity of sandy soils was evaluated. For the samples (R1 to R4)¡ the coefficient of permeability was 0.0051¡ 0.048¡ 0.076¡ and 0.19 cm/s respectively. Due to the limited range of input parameters¡ the method of Shahabi et al. can be used only for the R4 sample; so this method was discarded from statistical analysis. Comparing the results of laboratory test with common methods shows the methods of KozenyCarman and Chapuis and Aubertin were more accurate according to the highest R2 and lowest RE and RMSE. These methods were based on effective parameters and the results of accurate laboratory studies. The method of Mbonimpa et al. (2002) indicates the maximum deviation from observed values which may be due to the sensitivity of this model to void ratio (e). Also the results shows by increasing of void ratio the error of Mbonimpa et al. method increases.