Artificial Recharge on the River Beds in Urban Areas (Case Study: Karaj River)

Facts show that the level of groundwater has notably dropped in the Karaj River basin in recent ears. In the long term, this drop may ultimately reduce the quality of water resources and increase eh cost of waster extraction and cause the depletion of groundwater resources as the result of land settlement. Therefore, a solution to this problem should be found. This research examines the possibility of artificial recharge of the river in an area between Bilaghan diversion dam and grain mines near Sarhadabad in order to increase enhance the aquifer. Based on the facts and figures collected through piezometry wells over the last 30 years, it was concluded that the lever of groundwater has extremely lowered in recent years. In order to establish the existence of sufficient water for recharge, records of the years 1992-2003 were reviewed. The records show the flow of the river at the desired point is 92 million cubic meters per year. To determine the surface infiltration rate of the river bed, two representative infiltration pools were dug. The pools recorded water infiltration with a rate of 103 L/s.ha in a three-week period. Regarding the 150-hectare area of the river basin, above 1.3 million cubic meters of water may be depleted through infiltration and the same amount may be substituted through recharging. To examine the possibility of transmitting surface water to the aquifer, geological sections and texture of the underground soil layers have been evaluated, and regarding the absence of a clay layer with low penetrability and also because of the possibility of transmitting more than 2,000 cubic meters of water per day the feasibility of introducing surface water to groundwater resources was approved. To design the type of retarding structures on the river bed, two methods – balance slope and sediment movement threshold – have been compared. Since the results showed that inappreciable erosion occurs in the design conditions, therefore, the second method was selected as the appropriate alternative. Flood routing, using HEC-RAS computer software were used to design location and height of the retarding dams.