بررسي عملكرد شبكه پخش سيلاب موغار اردستان در تغذيه مصنوعي سفره هاي آب زيرزميني

Evaluation of the Moghar Floodwater Spreading System for the Artificial Recharge of Groundwater in Ardestan

Floodwater spreading system is an efficient and appropriate method for optimization of runoff utilization, particularly in arid and semirid regions. Beside the reduction of flood damages, this technique is also useful for artificial recharge, rangeland rehabilitation, and desertification control. The objective of this research was to evaluate the efficiency of Moghar floodwater spreading system which was designed and performed for artificial recharge of groundwater and for improving groundwater quality in the region. First, data on piezometric wells were collected. Then, infiltration rate as well as the physical properties of both sediments deposited in different strips and those of the natural soil of the area were determined. Groundwater samples from different irrigation wells as well as the flood water entered the system were taken and their chemical characteristics were evaluated. The results indicated that more than 100,000 tons of fine sediments with mean thickness of 43 cm and mostly containg silt-sized particles were deposited in the system. From the frist to fifth strip, the amount of sand content in the sediments decreased whereas the clay content increased. Consequently, the infiltration rate decreased from 1.35 cm/h in the first strip to 0.65 cm/h in the fifth one. Due to the formation of a thick and dense crust in different strips, their infiltration rate is not high. The second time flooding occurred in 1375 and seems to have had the highest influence on rising the groundwater level. Reduction of infiltration, evaporation of a very good quality floodwater, overuse of groundwater resources by farmers particularly in dry seasons, and the occurence of recent severe drought lowered the efficiency of this system. It seems that a great portion of water entering the system would be lost through evaporation if no measure is taken for reducing the floodwater turbidity. In conclusion it is highly recommended that an integrated watershed management system is implemented in the area in order to reduce the turbidity of floodwater, which in turn increases the profitabity of the system.