Storage required for Dar es Salaam municipal water supply.

The various methods of determining reservoir storage in water resources and their classification together with time series analysis leading to synthetic data generation were reviewed. A one-month low flow frequency curve was plotted for the Ruvu River from which recurrence intervals for failure of Dar es Salaam water supply without regulation of Ruvu River were estimated. The estimates were based on projected demands as critical flows. The results shows that for reliable supply of water to Dar es Salaam in the nearest future Ruvu River should be regulated. The storages that would be required by regulating Ruvu River or Wami River to ensure reliable supply of water to Dar es Salaam were also estimated. The estimates were based on the projected demand from the year 2005 - 2020 by JICA (1994). Thomas Fiering model was used for reliable reservoir storage capacity estimates. Forty traces each of 31 years and 30 years of monthly flows were generated for the Ruvu river and Wami river respectively using the model. Reservoir storages for the projected demands were determined by Behaviour Analysis method. The estimates were based on various design time based probability of failure of the storage. Reliability curves were plotted for each demand and design probability of failure for both rivers. The reliability curves are considered as useful decision tool in the choice of an appropriate storage capacity for a desired yield based on the choice of risk of the designer. Storage estimates of 99% reliability for each demand and probability of failure were determined from the reliability curves for both rivers. Comparison of the estimated storages from both rivers revealed that storage required on the Ruvu River is low. It has been recommended that the Ministry of Water on going drilling programme should be intensified whilst Ruvu awaits regulation.