Modeling groundwater flow under chaotic urbanization constraints in Kinshasa Capital Region (D.R. Congo)

Abstract

Groundwater is used as an alternative source of drinking water in the chaotically urbanized African mega city of Kinshasa (DR Congo). However, groundwater abstraction without proper management leads to aquifers mining. The main objective of this study was to better understand the regional groundwater flow regime and to build a groundwater management tool for an area of 2187.36 km2 using Visual MODFLOW Flex. The model's input data were collected 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 groundwater development scenarios. The recharge in the area is estimated at an average of 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 which was 0.24 m and root mean squared of 16.8 m. The results for the three (3) scenarios from the baseline, which comprised 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 River is located.