Modeling groundwater flow under chaotic urbanization constraints Kinshasa capital D.R Congo

The availability of drinking water is a challenge for the chaotically urbanized megacity of Kinshasa with population of over 10 million. REGIDESO, the national water supply company counts a daily deficit of 270,000 〖m˄〗^3/day. In order to cover this water deficit, groundwater is seen as an alternative. However, groundwater extraction without proper management may leads to aquifer depletion. The main objective of this study was to better understand the regional groundwater flow regime and to predict the effects of groundwater management in an area of 2187.36 〖km〗^2 using Visual MODFLOW Flex. To this end, the model’s petrophysics and hydrodynamics input data were collected or derived from various databases of national agencies and companies in charge of water engineering and management. Large scale steady-state and transient regional model was set up for the period 2000-2014, calibrated and validated to optimize groupwater development scenarios. The recharge in the area is estimated to be 236.21 mm/yr and is high in the southwest and less in paved areas and sandy-clayey soils in the east. The calibrated model had Nash-Sutcliffe Efficiency (NSE) coefficient of 0.9 and correlation coefficient of 0.98 and 0.96 for the steady-state and transient state, respectively. The accuracy of the calculated ground water levels was also judged by standard error of estimation at 0.24 m and root mean squared of 16.8 m. the results for the three (3) scenarios, which included increasing pumping rates by 10, 25 and 50%, indicated a further decrease in groundwater levels by 0.05m, 0.076m and 0.12 m, respectively. The modeled groundwater flow indicated that the flow direction for the whole study area is mainly from highlands towards lowlands, heading north, where the Congo Rover is located.