Fluctuations of water table level and quality in Niksar Plain

This study is done with the purpose of determining the change in groundwater depth and the quality of water in irrigated areas of Tokat-Niksar Plain. Sixty eight groundwater monitoring wells in the Niksar Plain are in active status. Monthly groundwater depth and electrical conductivity values were measured during the years of 2003 through 2019 by the State Hydraulic Works VII. District Tokat Directorate and/or Irrigation Units. Maps, graphs and charts indicating distributional water table depth, phreatic fluctuation obtained and the change of groundwater quality were generated by processing water quality results of local 18 deep weels at different times, and data obtained from the observation wells in computer environment on ArcGIS 10.3 software. The groundwater observation areas is determined as 6 364 ha. An apparent increase in water table levels was observed especially in the year of 2008. It was observed that pH values are between 6.70-8.50, electrical conductivity values are between 510-1 118 micromhos/cm in aquifer deep wells. In general, irrigation water quality was determined as C2S1. In the studied of 68 observation wells, pH is between 6.12-7.8, electrical conductivity is between 100-4 420 micromhos/cm. As a result of the evaluation of groundwater measurements monitored monthly, the area where the groundwater depth is 0-1 m is 924 ha (10%); 1-1.5 m is 2 980 ha (33%); 1.5-2 m is 969 ha (11%), 2-3 m is 719 ha (8%); 3-4 m is 2 836 ha (32%) and deeper than 4 m is 487 ha (6%). The month in which the irrigation water demand is the highest was determined as the month of August. It has been observed that agricultural irrigation activities have been increased, crop pattern has been diversified in the last decade. In addition, a proportional increase in the irrigation efficiency has been observed in the last decade. Studiously protecting and augmenting observation wells and boreholes, increasing the number of them, and frequent monitoring activities are advised. The monitoring of the water table depths and salinity of the groundwater should be continued carefully. 2019, 143 PAGE KEYWORDS: Niksar Plain, Water table, Groundwater, Observation well, Salinity, Hydrogeology, Aquifer