Evaluate effect of soil texture and transport length on conservative tracer dispersion rate using solute transport models

Determination of the best method to estimate the dispersion rate is very important to ensure accuracy of the computed data. The aim of this research is studying of transport length effects of dispersion of conservative tracer Nacl in soils with different texture using several solute transport models including Brigham، Fried-Combernous and solutions of the advection-dispersion equation with inverse CXTFIT application. Two types of sand (quicksand and gravel with medium-textured) with 4 different textures in the 3 soil columns lengths 25، 40 and 55 cm was used. Conservative tracer NaCl with constant concentration 3. 47 m. S/cm under one-dimensional steady flow was directed into the top of the soil column. The results showed that by increasing the length of columns the dispersion rate will be increased and in composite soil texture the dispersivity coefficient (α) was more than a homogeneous texture and grain. Comparison of three methods shows that by reducing the transport length the Brigham model and by increasing the transport length، the model base on CXTFIT code is better. In all cases، the results of Fried-Combernous model had a noticeable difference between the other two models.