Abstract:
Management of groundwater resources can be
improved by using groundwater models to perform risk
analyses and to improve development strategies, but a lack
of extensive basic data often limits the implementation of
sophisticated models. Dar es Salaam in Tanzania is an
example of a city where increasing groundwater use in a
Pleistocene aquifer is causing groundwater-related problems
such as saline intrusion along the coastline, lowering
of water-table levels, and contamination of pumping
wells. The lack of a water-level monitoring network
introduces a problem for basic data collection and model
calibration and validation. As a replacement, local watersupply
wells were used for measuring groundwater depth,
and well-top heights were estimated from a regional
digital elevation model to recalculate water depths to
hydraulic heads. These were used to draw a regional
piezometric map. Hydraulic parameters were estimated
from short-time pumping tests in the local wells, but
variation in hydraulic conductivity was attributed to
uncertainty in well characteristics (information often
unavailable) and not to aquifer heterogeneity. A MODFLOW
model was calibrated with a homogeneous
hydraulic conductivity field and a sensitivity analysis
between the conductivity and aquifer recharge showed
that average annual recharge will likely be in the range
80–100mm/year.
