DEVELOPMENT, CALIBRATION AND VALIDATION OF A MACRO - CATCHMENT RAIN WATER HARVESTING MODEL: OVERCOMING LIMITED HYDROLOGICAL DATA IN SEMI-ARID AREAS OF TANZANIA

Rainwater harvesting (RWH) has become a critical water conservation method throughout the world. Success of RWH depends upon efficient design based on accurate hydrological modelling Model designed specifically to macro catchments RWH are very few and site specific. This study therefore report on development, calibration and validation of a Macro catchment RWH in the area with limited hydrological data in semi arid areas of Tanzania. Macro catchment model was developed from modifying Parched Thirst (PT) rainwater harvesting model for micro catchments systems. Conceptual model modeling, coding and performance testing were conducted at Newcastle upon Tyne University. Calibration and validation were carried out in Mwembe – Makanya catchment in Same District in Kilimanjaro region. Two experimental models were set for runoff generation and data were collected for two rainy seasons from each site. Three tests were conducted to validate the model: runoff amount for single and significant storms; total monthly runoff and seasonal runoff over the 2-years period. The result showed that the model was able to simulate macro catchment rainwater harvesting in slope between 3 15%, Validation results showed high correlation between observed and simulated runoff during long rainy season (R2 0.98). The study was able to establish a boundary scenario which can assist in validation of simulation of runoff in ungauged catchment. The model for the macro catchment RWH system included runoff generation and routing. The addition of the routing component enabled the model to simulate runoff in large catchments. The Parched Thirst (PT) model for macro catchment can be used in simulation of runoff from large catchments. The model can also be used in planning of water resources in other sectors requiring estimation of long term series of runoff records.