HYDROGEOLOGY OF NIKSAR BASIN, TOKAT, TURKEY

The study area comprises the Niksar Basin of Tokat district, located in the Middle Black Sea region, Turkey. The Kelkit River flows through the center of Niksar Valley. The lithological units exposed on the northern and southern part of Kelkit River have disparate geological sequences; grouped as "Pontid" and "Anatolid" respectively. The micritic and biomicritic limestone of Upper Jurassic - Lower Cretaceous, limestone of Upper Cretaceous and the detrital limestone of Upper Cretaceous - Lower Paleocene form characteristic karstic aquifers. In the valley a thick sequence of loose gravel, sand and clayey materials of Pliocene and Quaternary is deposited. The presence of clay lenses in these materials created suitable hydrodynamic conditions for the formation of confined aquifer. The Karstic aquifers recharged through precipitation and valley-fill aquifer through Kelkit River. These aquifers fulfill water supply demands of entire population of Niksar Town and surrounding villages. This paper summarizes hydrogeological research conducted on all basinal formations. The Karstic aquifers and the unconfined aquifer of valley-fill sediments systematically analyzed. The physical characteristics of the aquifer formations, karstification, occurrence and movement of groundwater, recharge and discharge sources and discharge hydrograph analysis were conducted. The discharge rate of five major karstic spring ranges from 55 to 430 l/s and the average storage capacity from 0.24x10⁶m³ to 2.24x10⁶m³. The groundwater budget of valley-fill aquifer represents that during the study period aquifer received 2.33x10⁹m³ and discharged 2.63x10⁹m³ of groundwater.