| Evapotranspiration (ET) covers are receiving an increasing amount of attention for use at waste disposal sites. Instead of using barrier layers like conventional covers, percolation in ET cover system is minimized by water balance components which store the water prior to its transpiration through vegetation or evaporation from the soil surface. Vegetation for an ET cover must be suitable for its particular locality and have well-developed root systems, since they promote transpiration and contribute to the long-term performance of the cover. They pull water out of the cover soil and release it into the environment, thereby decreasing the percolation of water through the cover and increasing the amount of transpiration that takes place through the roots. Unusually deep rooted vegetation, however, can penetrate the waste area, resulting in the transport of constituents to the above-ground biomass. Thus, determination of root length is very important for the ET cover design. But, the study of plant roots conventionally includes destructive and time-consuming methods. Destructive methods do not allow root measurements to be repeated at the same location, but only a handful of studies focus on non-destructive root studies, which are restricted by the soil and root type. Among the non-destructive techniques, electrical resistivity imaging is one of the most popular methods. Resistivity Imaging (RI) is a non-destructive method used to investigate the subsurface condition, during which an electrical current is applied to the soil through conductors known as electrodes, so that the differences in the electrical potential at each specified location can be measured. It is considered that, roots affect in creating difference in electrical potential. The difference in potential creates the feasibility for studying root properties in the soil by electrical resistivity imaging. The objective of the current study was to determine the root length of vegetation in an ET cover soil, using the RI method. Two ET covers located in two slopes at the City of Irving Landfill in Irving, Texas were investigated, using the RI method, to estimate root length. The determination of the root length was also studied based on the minirhizotron technique to measure the actual root length in the site. The estimated root lengths were compared with the actual root lengths. The estimated root lengths were 1.9 feet and 1.2 feet, whereas corresponding actual root lengths were 1.75 feet and 1 foot, respectively. An analytical model was developed to determine the root length based on its relationship with resistivity and precipitation. Predicted root lengths from the developed model were within a band of 15% error margin of the actual root lengths, indicating good agreement between the actual and predicted values. |
