Browsing by Author "Bakundukize, Charles"

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Investigating seawater intrusion due to groundwater pumping with schematic model simulations: The example of the Dar es Salaam coastal aquifer in Tanzania
(Elsevier, 2014) Camp, Marc Van; Mtoni, Yohana; Mjemah, Ibrahimu C.; Bakundukize, Charles; Walraevens, Kristine
Water supply requirements in Dar es Salaam city (Tanzania) are rising rapidly by population growth and groundwater is increasingly used to fullfill the needs. The groundwater is taken from the Dar es Salaam Quaternary coastal aquifer (DQCA), stretching inland from the coastline. As thousands of wells have been drilled in the coastal strip and pumping rates are uncontrolled, seawater intrusion is deteriorating the quality of fresh groundwater. To investigate the response of the fresh/salt water interface to coastal pumping, simulations with a schematic two-dimensional cross-sectional model have been done. Depending on the depth of the wells in the 150 m thick DQCA and their distance from the coastline, different pathways of seawater intrusion and shifts of the interface can be recognized. The local presence of a semi-pervious layer can have a significant impact on the fresh/salt water distribution. Although the modeled section is not related to a specific location along the coastline but rather represents an average aquifer buildup, the results of the simulations can be used to formulate recommendations when drilling new wells and for a better monitoring of the salinisation process along the coast. It proves that even simple schematic models can give meaningful contributions
Saltwater intrusion and nitrate pollution in the coastal aquifer of Dar es Salaam, Tanzania.
(Springer, Environimental Earth Science., 2013-11-03) Mtoni, Yohana; Mjemah, Ibrahimu Chikira; Bakundukize, Charles; Van Camp, Marc; Martenes, Kristine; Walraevens, Kristine
Dar es Salaam Quaternary coastal aquifer is a major source of water supply in Dar es Salaam City used for domestic, agricultural, and industrial uses. However, groundwater overdraft and contamination are the major problems affecting the aquifer system. This study aims to define the principal hydrogeochemical processes control- ling groundwater quality in the coastal strip of Dar es Salaam and to investigate whether the threats of seawater intrusion and pollution are influencing groundwater qual- ity. Major cations and anions analysed in 134 groundwater samples reveal that groundwater is mainly affected by four factors: dissolution of calcite and dolomite, weathering of silicate minerals, seawater intrusion due to aquifer over- exploitation, and nitrate pollution mainly caused by the use of pit latrines and septic tanks. High enrichment of Na ? and Cl - near the coast gives an indication of seawater intrusion into the aquifer as also supported from the Na–Cl signature on the Piper diagram. The boreholes close to the coast have much higher Na/Cl molar ratios than the boreholes located further inland. The dissolution of calcite and dolomite in recharge areas results in Ca–HCO 3 and Ca–Mg–HCO 3 groundwater types. Further along flow paths, Ca 2? and Na ? ion exchange causes groundwater evolution to Na–HCO 3 type. From the PHREEQC simu- lation model, it appears that groundwater is undersaturated to slightly oversaturated with respect to the calcite and dolomite minerals. The results of this study provide important information required for the protection of the aquifer system.