The Artificial Recharge of Hashtgerd Plain (NW of Iran) HOMAYOUN MOGHIMI Geology University of Payam-e Noor No. 8, 5 th Alley, Baluchestan St., Gisha St., Tehran IRAN Abstract: The climate of Iran is arid and semi-arid. One of the regions affected by excessive exploitation of ground water resources is Hashtgerd plain in the north west of Iran. To prevent the ground water level fall_ 2 to 4 m during the past ten years_ the Artificial Recharge Plan is suggested. The water required is provided from the Kordan River which has an average recharge volume of 3.5m³/s from February to May. Hydrogeologically, experiment results show that the alluvium has transmissibility of about 3500 m²/day, vertical and horizontal hydraulic conductivity of 2 and 14 m/day, and the storage coefficient of 7% to 9%. To calculate the basin dimensions Houisman, and for the ground water level rise after artificial recharge, Hantush and Todd methods are applied. Key-word: Artificial recharge, infiltration basin, rise, Houisman method, Hantush method, Todd method. 1 Introduction In recent years, the growing flow of population and consequently excessive use of water resources in Iran, which is considered as an arid and semiarid area has led to perilous results. One of the solutions is the optimized use of surface water resources and transmitting them to ground water. In this respect, concerning the geological, climactic, water resource potentiality, industrial, etc conditions, and different methods of artificial resources can be used. The primary researches and artificial recharge has been done in Ghazvin plain in 1969, Varamin (SE of Tehran) and Naz (NE of Iran in Caspian Sea basin) plains in Sari [2, 9 ]. Due to excessive use of water resources in Hashtgerd plain and in order to enrich it, artificial recharge has been suggested. Present study is an attempt to analyze the optimal method and location of artificial recharge and its effect on the aquifer. 2 Procedure and Methodology Hashtgerd plain is about 583.4 Km 2 . The area is located between latitude of 36 ˚ , 45 ΄ - 36 ˚ , 05 ΄ and longitude of 50 ˚ , 30 ΄ - 50 ˚ , 55 ΄ (fig.1), and suggested for artificial recharge (fig. 2) is situated in the south of Kordan Village. The area is formed by plioquaternary alluvia and is of great significance from the hydrogeological point of view. Rieben [3] has analyzed these alluvia and divided them into four series of A (Hezardereh series), B (Kahrizak series), C (Tehran series), and D (fig. 2) [3] as follows in table1: Table 1 Geological specifications of Hashtgerd plain and artificial recharge area Series Geological Specifications Age D Cobble and gravel, sand Recent Era C Gravel, sand, silt and clay; forms the main aquifer; significant thickness, high permeability; more tiny-grain materials as you go towards the south (Rieben, 1955) Quaternary B weak cement, gravel and sand, and silt; darker and more heterogenic than A (Rieben, 1955), unconformity with A series plio- Pleistocene A Conglomerate, sand and gravel and lime, semi-hard cement; Dip 5˚ to 20˚ toward the south (Rieben, 1955) unconformity with Upper Red Form. & E Form. Pliocene M Upper Red formation; evaporative sediment (gypsum, anhydrate) Clay & Silt stone, unconformity E&A series Upper Miocene E Volcanic Material (Andesine, Tuff, Basalt, Shale), limestone and agglomerate Eocene 2.1 Meteorology of Hashtgerd Plain The average annual temperature of the Kordan River drainage basin is 8.7˚ C and of Hashtgerd plain is13.2˚ C (Karimabad station). To analyze the annual range of evaporation in this area, Karimabad station is used. This range is about 2000 to 2300 mm in the plain area; the maximum range refers to June and July and the minimum range refers to January and February. Regarding the 25 year precipitation statistical information in Karimabad and Kordan (Dehesomee) stations, the annual Proceedings of the 5th WSEAS International Conference on Environment, Ecosystems and Development, Venice, Italy, November 20-22, 2006 413