Citation: Aziz, A.; Berndtsson, R.; Attia, T.; Hamed, Y.; Selim, T. Noninvasive Monitoring of Subsurface Soil Conditions to Evaluate the Efficacy of Mole Drain in Heavy Clay Soils. Water 2023, 15, 110. https://doi.org/10.3390/w15010110 Academic Editors: Patrícia Palma and Alexandra Tomaz Received: 22 November 2022 Revised: 22 December 2022 Accepted: 26 December 2022 Published: 29 December 2022 Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). water Article Noninvasive Monitoring of Subsurface Soil Conditions to Evaluate the Efficacy of Mole Drain in Heavy Clay Soils Akram Aziz 1 , Ronny Berndtsson 2, * , Tamer Attia 1 , Yasser Hamed 3 and Tarek Selim 3, * 1 Geology Department, Faculty of Science, Port Said University, Port Said 42522, Egypt 2 Centre for Advanced Middle Eastern Studies & Division of Water Resources Engineering, Lund University, SE-22100 Lund, Sweden 3 Civil Engineering Department, Faculty of Engineering, Port Said University, Port Said 42523, Egypt * Correspondence: ronny.berndtsson@tvrl.lth.se (R.B.); eng_tarek_selim@yahoo.com (T.S.) Abstract: Soil degradation and low productivity are among the major agricultural problems facing farmers of the newly reclaimed agricultural area in the Nile Delta region, Egypt. High content of clay and silt characterizes the soil texture of all farms in the area, while farmers still rely on the traditional mole drainage (MD) system to reduce the salinity of the farm soil. We present a comparison of innovative geo-resistivity methods to evaluate mole drains and the salinity affected clay soils. Geoelectrical surveys were conducted on three newly reclaimed farms to image the subsurface soil drainage conditions and to evaluate the efficiency of using the traditional MD systems in these heavy clay environments. The surveys included measuring the natural spontaneous potential (SP), apparent resistivity gradient (RG), and electrical resistivity tomography (ERT). Integrating the results of the three methods reduced the ambiguous interpretation of the inverted ERT models and allowed us to determine the subsurface soil structure. The inverted ERT models were suitable for locating the buried MDs and delineating the upper surface of the undisturbed clay beds. The proximity of these layers to the topsoil reduces the role played by MDs in draining the soil in the first farm and prevents the growth of deep-rooted plants in the second farm. Time-lapse ERT measurements on the third farm revealed a defect in its drainage network where the slope of the clay beds opposes the main direction of the MDs. That has completely obstructed the drainage system of the farm and caused waterlogging. The presented geo-resistivity methods show that integrated models can be used to improve the assessment of in situ sub-surface drainage in clay-rich soils. Keywords: water logging; resistivity gradient; ERT; electrical conductivity; soil drainage 1. Introduction Most countries in the Middle East include large arid and semi-arid climate regions [1]. They all face the challenge of securing enough food supplies in unfavorable dry climate conditions with water scarcity. They need not only to conserve their existing resources (e.g., water, cultivated areas, etc.) but also to maximize the utilization of their resources. In Egypt, the government has launched a national project for land reclamation to meet the increasing food demands of its 110 million population. The area south of Port Said city (Figure 1a,b) is one of the main sectors in that project, as its production serves the districts of the Suez Canal and northern Sinai regions [2,3]. This area was once a fertile region in ancient Egypt [4–6]. Currently, the area is characterized by low precipitation—around 150 mm annually—and high evapotranspiration rates. The temperature ranges from 31 ◦ to 36 ◦ C during July/August, and from 8 ◦ to 19 ◦ C during December/January [7]. Local farmers mainly rely on the use of the traditional mole drain (MD) method to increase the drainage of the clay-rich soils. Mole drains are sets of unlined soil channels dug by a mole plow. The plow consists of a cylindrical foot attached to a narrow shank followed by a cylindrical expander. The shank creates a narrow slot extending from the soil surface down Water 2023, 15, 110. https://doi.org/10.3390/w15010110 https://www.mdpi.com/journal/water