FLOODWATER MANAGEMENT THROUGH SPREADING OF IT AND STORAGE IN AQUIFER AND ITS IMPACTS ON AGRICULTURAL WATER SUPPLY CASE STUDY : PART OF ZANJAN PLAIN, IRAN

摘要

The changes of land use (rainfed and released areas to irrigated lands) needs utilization and optimization methods for harvesting of base flow and flood water. Therefore, the floodwater harvesting and its recharging and storage within the aquifer can be considered as an utilization and optimization method for floods. The study basin is located in the part of the Zanjan plain, in the northwest of Iran, this function has been achieved by constructing a spreading system in the part of Zanjan plain. This area is located between two rivers of Sohrain and Gharecharian. The most part of the plain is under rainfed and released dry lands. This paper is attempting to evaluate the impact of water spreading on vegetation (cover and production), water supply for agricultural activities on the spreading area as the landuse changes (rainfed and dry land to irrigated land) due to increasing the qanat discharge and construction of wells. Mean vegetation cover percentage in the spread area during five years (1999-2003) increased from 22.22 to 56.18% and standing crop production changed from 733.4 to 2541.8 Kg/ha. The discharge of qanats increased in downlands of spread area. In one case it caused an increase of the cultivated alfalfa area from 3 to 6.5 ha and in another case the water supply for a garden of 10 ha was improved. Aguaculturing activities were also started in these qanats. In addition, rise of the ground water table in this part of the plain led to construction of 10 exploitation wells resulting in changing of 300 ha of rainfed and released areas into irrigated land. It seems that floodwater harvesting and its spreading and storage in aquifer can be considered as one of the managing aspects for water resources that can play an effective role in sustainable development on agriculture and natural resources.