Field Evaluation of Some of the Grain-size Analysis Methods for Determining Hydraulic Conductivity of Streambed

To determine the water exchanges between surface and ground waters through river bed, it is necessary to have an accurate estimation of hydraulic conductivity of the river bed. But, the measurement of river bed hydraulic conductivity is difficult, time-consuming and costly. The grain size analysis methods estimate the hydraulic conductivity using the data obtained from the grain size distribution curve and the porosity of the soil, without any field measurements. The purpose of this study is to compare the estimated hydraulic conductivities, using some grain-size analysis equations (Kg), with the values measured by permeameter (Kv) method in Karkheh, Dez and, Shavoor river beds in Shush County, Khuzestan Province. In this study, the accuracy of seven empirical equations were investigated using 18 samples obtained from the measuring stations. The Kv values at Karkheh, Dez, and Shavoor river bed were measured to be 2.15, 2.94 and 0.03 m/day, respectively. In Shavoor River bed with clay texture, all the equations overestimate the Kg up to 84.6 times more than the Kv. While, in the other rivers with coarse grains, the estimated Kg by Alyamani-sen was less than the Kv, and the Kg estimated by Terzaghi, Hazen, Beyer and USBR was more than the Kv and the Kg estimated by Slichter and Kozney equations resulted a Kg close to the Kv. Moreover, the ratio of the new proposed C coefficient to the original C coefficient of equations were calculated between "0.15 to 2.1". Based on the results, it is necessary to use the modified coefficient of C for utilization of grain size methods.