Visualizing Subsoil Structure for Evaluating the Efficiency of Mole Drain in Heavy Clay Soils Using Geo-electrical Methods

Abstract

Geo-electrical surveys have been conducted on three newly reclaimed farms located on the northeastern corner of the Nile Delta, Egypt. These farms always suffer from various soil salinization problems. The surveys include measuring the natural Spontaneous Potential (SP) of the soil, apparent Resistivity Gradient (RG), and Electrical Resistivity Tomography (ERT). The study aims to image the soil structure and evaluate the effectiveness of the traditional Mole Drainage (MD) systems that are customarily utilized to reduce soil salinity of the farms in this region. Integrating the results of the surveys conducted on the first farm shows that the subsurface heavy clay-bed is very close to the topsoil. This proximity reduces the role of the MD in draining the soil. On the second farm, the clay-bed did not reach the soil surface of the farm, and a significant reduction in soil salinity levels nearby the Mole drains was observed. However, the limited thickness of the root zone was not sufficient to plant deep-rooted vegetation. Repeating the ERT measurements on the third (barren) farm revealed a severe defect in the farm drainage network, where the slope of the clay-bed opposes the main direction of the surface drainage system of the farm. This has resulted in groundwater accumulation and a frequent occurrence of waterlogging.Eventually, the efficiency of any drainage network does not depend solely on its surface maintenance. It is important to figure out the subsurface conditions of the soil as well. The methods have proven to be effective and applicable tools in imaging soil subsurface conditions nondestructively, even in lands characterized by high clay content.