The presentresearch aimstoestimatetheamountofsurfacerunoffandrunoffcoefficientin Tel-Abta areawest oftheprovinceofNineveh for the purpose of designing and management of small scale rainwater harvesting systems. Daily rainfall data at Tel-Abta for the period (1996 – 2012) are used. The mean annual rainfall for this period is 164 mm. Two computer codes, using EXCEL Programming are developed; one is based on the SCS CurveNumberMethod "SCS- CN" and the other one is based onthe method of Threshold Rain "TR". The study revealed that the TR method resulted in average annual amounts of surface runoff greater than that of the SCS method (23 mmversus 16 mm; respectively).On average, the runoff coefficient at Tel- Abta is in the range of 0.062 to 0.24. Finally, simple equations were proposed to estimate, at Tel Abta area, the runoff coefficient dependingonthe characteristics of the monthlyrainfallin thestudyarea.
Keywords: Water harvesting, Runoff Coefficient, Threshold Rain Method, SCS Curve Number Method, Rainfall analysis