Abstract:
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
