Evaluation Of Groundwater In Selected Urban Areas Of The Khartoum State

Abstract

The developing residential areas in the capital and the increasing population growth have caused serious problems, regarding groundwater quality and supply. The water levels in the supply wells during the summer season become deeper and water pumps have to be fitted with extra pipes. However, the degradation of the water quality caused by the seeping effluents is clearly identified in some areas. Consequently, this has led to the detailed investigation of this study. This research objectives aim at the investigation of the decline of the groundwater levels in Khartoum and towards the better characterization of the groundwater quality and the hydro chemical processes responsible for the groundwater mineral content. A total of 54 supply wells within Khartoum were selected for field and laboratory analysis. The criterion followed in the selection of the supply wells was to sample the heavily pumped wells due to dense population. Groundwater samples were collected at four months interval for a period of two years starting June 2004 to June 2006 from the supply wells located in Khartoum, Omdurman and Khartoum North (Bahri) for physical and chemical major ions analysis. The results of the chemical analysis and water levels investigations were presented in figures and maps using different software. The overall objective of the study is to derive better understanding for the quality, flow and supply of the groundwater in the state. The study also tried to understand the contribution of the River Nile waters to the groundwater where the groundwater quality in the study areas is strongly affected by the River Nile water chemistry as well as the Nile’s floods and droughts. The reason behind the drop of water levels in the area, according to the geological cross sections, is the presence of thick clays in the study areas of Khartoum, Omdurman and Khartoum North. The clays caused reduction in the hydraulic conductivity as well as it retarded the flow of water. The cross sections also indicated poor well designs especially in Omdurman study area where screens are located on clays. Chemically, the study showed that in Khartoum study area, the groundwater type is Calcium-Magnesium bicarbonate rich at the Blue Nile side wells, Sodium-Potassium sulphate rich at the supply wells located further away from the Niles and Sodium- Potassium bicarbonate rich at the wells located near the White Nile side. The water samples indicate high contents of Chlorides and Nitrates. The water salinity is attributed to the presence of the calcareous kanker nodules and pebbles.