Application of Geomodeller in Production of Enhanced Lithological Map for Groundwater Exploration

Abstract

Abstract
Lithology is one of the major controlling factors considered in groundwater potential mapping. The factor is considered because it controls the recharge rate from rain water that forms groundwater table. Lithology has always been derived from geological maps of a region through digitization of different units constituting the geology of the area. However, developed geological map excludes unconsolidated material within which groundwater aquifers are developed. The aim of the study was to develop the protocol for deriving lithology thematic maps within soil, laterite, saprolite, and granite in Tochi watershed for use in groundwater potential mapping. The method utilized data derived from borehole drill logs, the geology map of Uganda for extraction of unique features, and a Digital Elevation Model (DEM) to develop input data required by Geomodeller 3.2.0 software. From the 3D model of Tochi watershed generated, transverse and longitudinal sections were created to gain insight into subsurface lithological arrangement through visual interpretation. In order to develop a thematic map of mentioned lithology, point elevation data of 3D lithological boundary surfaces were exported in excel format for further analysis in ArcGIS. A Triangular Irregular Network (TIN) was generated from the imported data of individual stratigraphic units. The TIN was converted to DEM followed by reclassification into four lithology thematic maps namely; very high, high, low, and very low. The result revealed that soil formed patches mainly at lowland areas exposing laterite to the topographic land surface due to erosion and deposition regimes. Laterite occupied the slopy section within the watershed and also does not exist as a continuous series. The same trend applies to saprolite whose exposure to the land surface is exhibited at the foothills of hilly areas. Granite was exposed to land surface at the highest elevation within the watershed and formed more less a continuous series. From the thematic maps developed, highest groundwater potential was exhibited in lowland areas where strike slip fault exists. The potential reduced with increase in elevation. The finding shows that the developed protocol, which is user friendly can enhance the development of lithological map from groundwater drill logs using the Geomodeller tool. The map can be used to clearly identify groundwater recharge zones for effective management of the groundwater resource.