Evaluation of Net Recharge in Al Salt Urban Area/ Jordan Using Scs Curve Number Method

Amany Ta’any, Rakad Ta'any, Omar Rimawi and Ali Elnaqa

Al Balqa’ Applied University, Faculty of Agricultural Technology, As Salt 19117 Jordan.

ABSTRACT: This study deals with the calculation of net recharge at Al Salt urban area. The “Net Recharge” is the annual total quantity of water which infiltrates from the ground surface to the aquifer. It is expressed as the annual recharge rate (mm/year) evaluated on the basis of field measurements, derived from the water balance equation, or estimated with the help of aerial photographs or satellite imagery. Precipitation is the primary source of groundwater because it seeps through the unsaturated zone to the water table. The amount and quality of recharge significantly affects the physical and chemical processes in the soil-rock-groundwater system. The greater the recharge the greater the contamination potential because, it may lead to leaching and transporting contaminants from the ground surface to the water table. In the present research the water balance equation was applied to calculate the net recharge in the study area. This equation was used to perform the water balance on daily basis for each storm event during the period under investigation. Rainfall is usually concentrated between December and March; in this period rainfall duration is long and evaporation is low, so that it can be concluded that recharge occurs mostly during this period. The rainfall is the only parameter in the study area; therefore, daily rainfall and initial abstraction were calculated from five rainfall stations using the SCS-Curve Number method for each storm during a specific year. The potential evaporation was computed using Penman Equation, and then the water balance was solved for all storms that occurred during the period of the water years (1989-2007). The calculated average annual recharge to the upper aquifer was about 10 MCM. The recharge rate ranges between 9.6 and 12.2 %. In general, the mean groundwater ranges from about 20 – 80 mm/year. The rating for the recharge parameter in the studied area ranges from 1 to 3. The highest value refers to higher recharge rate and the lowest value indicates the lower recharge.

KEYWORDS: Rainfall; net recharge; aquifer; contamination; balance; DRASTIC; Jordan

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