Browsing by Author "Martenes, Kristine"

Now showing 1 - 2 of 2

Groundwater exploitation and recharge rate estimation of a quaternary sand aquifer in Dar-es-Salaam area, Tanzania
(Springer-Verlag, 2010-09-10) Mjemah, Ibrahimu Chikira; Van Camp, Marc; Martenes, Kristine; Walraevens, Kristine
Dar-es-Salaam City gets water supply from surface water and groundwater. The groundwater is used to supplement surface water supply and has increasingly become a major source of water supply in the city. The study area comprises three major parts: the central coastal plain with quaternary fluvial–deltaic sediments, the deltaic Mio-Pliocene clay-bound sands and gravels in the north- west and southeast and the Lower Miocene fluviatile sandstones of Pugu Hills in the west of the study area. The main objective of this study was to quantify the integrated water balance. The major source of renewable groundwater in the aquifer is rainfall. Hence, the average recharge of 256.2 mm/year (for the year 2006) to the aquifer was estimated using the balance method of Thornthwaite and Mather, which is equal to 99.4 hm 3 /year for the whole alluvial aquifer. This value was balanced with total groundwater abstraction of 8.59 hm 3 /year, baseflow to rivers of 75.7 hm 3 /year and discharge into the sea (15.11 hm 3 /year).
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.