Development and application of hydrological decision support tools Pangani River Basin in Tanzania.

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University of Dar es Salaam
Various stand-alone Decision Support Tools were developed for describing and highlighting the major hydrological variables (decision issues) in Pangani River Basin. The tools consist of Spatial Rainfall (RAIN GEOSTAT), Evaporation (EVAP-DSS), Soil Moisture (D CSMB) and Integrated Water Resources Assessment Model (IWRAMP). The three spatial models were used to estimate spatial rainfall, evaporation and soil moisture variables in the entire Pangani basin for the benefit of hydrological and agricultural planning purposes. The spatial rainfall and evaporation estimates were further improved by incorporating digital elevation model (DEM) underscoring the influence of elevation in Pangani basin. The soil moisture model (D CSMB) was used to assess sustainability of rainfed agriculture in the basin. It was showed that it is practically impossible to depend entirely on rain fed agriculture without supplementary irrigation confirming the already existing situation of extensive irrigation practice in the basin. The IWRAMP model was developed to address the major management issues of the basin and highlighted three major findings 1). It was found that the NYM reservoir was not efficiently operated and alternative operation procedure was developed. The new procedure improves the long term release by as much as 4 m3/s, minimizes the spill and maintains minimum storage level at acceptable levels; 2) Kirua swamp was identified as a major water losing swamp specially when water release from the reservoir exceeds 30 m3/s. This undermines the improved release situation from NYM reservoir, which would otherwise boost the hydropower production at Hale and Pangani Fall. Thus, the gain in water release from the reservoir should either be accompanied by improved channel system (such as construction of river training works) or irrigation may be encouraged in areas between the reservoir and the swamp to convert the additional water for beneficial use and 3) if the new reservoir operation procedure is strictly followed, in normal hydrological years an additional area of 10,000 ha can be brought under irrigation upstream of NYM reservoir. Finally, the study results should be viewed in the context of the study period and needs further improvement as new data becomes available.
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Hydrology, Pangani river basin, Watershed, Runoff
Moges, S. A. (2003). Development and application of hydrological decision support tools Pangani River Basin in Tanzania. Masters dissertation, University of Dar es Salaam. Available at (