Abstract:
Water balance for Dar es Salaam Quaternary coastal aquifer
(DQCA) was calculated according to the method of Thornthwaite and Mather.
Monthly potential evapotranspiration estimates were calculated from 39 years
(1971–2009) of routine meteorological data using Penman-Monteith,
Thornthwaite, Hargreaves and Hamon methods. Results were compared in order
to show possible differences that could be attributed to the methods.
Determination of groundwater recharge rates gave a mean value of 184 mm year -1
which is equivalent to 71.39 x 10 6 m 3 year -1 indicating that 16.5% of the long term
average annual precipitation of 1114 mm ends up as groundwater recharge.
Groundwater abstraction from DQCA was estimated to be 69.3 x 10 6 m 3 year -1 .
These results are alarming in two aspects: high abstraction rate and the increasing
trend of borehole drilling. Groundwater abstraction which is nearly equal to the
amount of the groundwater recharge is far greater than the least conservative
sustainable yield calculated at 70% (equivalent to 49.97 x 10 6 m 3 year -1 ).
