Application of Isotope and Dye Tracing Methods in Hydrology

Iran with an annual average precipitation rate of 260 ml is included as arid and semi-arid regions of the world. So, water scarcity as a primitive problem has caused undevelopment in agricultural, economic, social and industrial fields. Constructing dams across the rivers is one of the most accepted methods to control and exploit surface waters. Reservoirs formed by constructing dams make fluvial morphology changes from a river-course form into a lakewise one. This makes changes into groundwater flow behavior at the dam site, i.e. a kind of conversion takes place from the role of the aquifers as a recharge source for the rivers before dam construction into making the river - reservoir - as the recharge source for the aquifer. As a result, water leakage might occur in the reservoir. Isotope and dye tracing methods could be then used to investigate cases such as: present condition of the river, the process of surface water leakage into aquifers, specifying water leakage locations, the relationships between different water resources, age, class, type, velocity and direction of groundwater flows, the status of permeability of formations of the reservoir, karst development, etc. (author)