Determining the Effects of Runoff Area Situation on Threshold Runoff and Water Storage Profile Under Micro Catchment Water Harvesting Systems

In order to investigate the roles of water harvesting patterns in water saving and increasing rain water productivity under micro catchment water harvesting systems، a field experiment was conducted in East Azarbaijan in the northwest of Iran during 1999-2006. The treatments included two MCWH patterns (small basins and semi-circular bunds)، three catchment sizes (25m2; 49m2 and 81m2)، three runoff area treatments (Natural، cleared and smoothed، wetting and compacting) and two infiltration areas (Natural، soil mixed with polymer at a rate of 1kg/tree) for two new almond varieties. Polymer had no significant effect on water holding. Although the small basin with (9×9)، runoff area compacted and use of polymer gave better results in survival، the growth and productivity of almond، the treatment with small basin (7×7) with compaction and without polymer can be recommended based on an economic analysis. Threshold runoffs were measured to be 2. 5-3. 5، 3. 5-4. 5 and 4. 5-5. 5 mm for natural، cleaned and smoothed، cleaned، wetted and compacted condite، respectively. Seventeen-year (1996-2013) average rainfall is equal to 202 mm، which shows that 84. 4، 65. 3، 51. 3 and 36. 4 of the total precipitation were more than 2، 4، 6 and 8 mm، respectively. Maximum rainfall runoff coefficient for threshold rain of 2، 4، 6 and 8 mm، was obtained to be 0. 57، 0. 35، 0. 22 and 0. 14، respectively. The design runoff coefficient for threshold rain of 2، 4، 6 and 8 mm، was obtained to be 0. 28، 0. 17، 0. 11 and 0. 07، respectively. Determination of threshold runoff has a major role in the success of water harvesting system design.