Journal of Himalayan Earth Sciences Volume 54, No. 1, 2021 pp. 69-89 Hydrogeological and Groundwater Investigations of Basin, Tokat,

Syed Mobasher Aftab1* 1Balochistan University of Information Technology, Engineering & Management Sciences, Quetta *Corresponding author's email: [email protected] Submitted date: 03/06/2020 Accepted date: 24/02/2021 Published online: 31/03/2021 Abstract

The study area comprises the Niksar Basin of Tokat district, located in the Middle , Turkey. The River flows through the center of Niksar Valley. The lithological units exposed on the northern and southern parts of Kelkit River have disparate geological sequences; grouped as "Pontid" and "Anatolit" 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 are deposited. The presence of clay lenses in these materials created suitable hydrodynamic conditions for the formation of confined and unconfined aquifers. The karstic aquifers recharged through precipitation and valley-fill aquifer through Kelkit River. These aquifers fulfill the water supply demands of the 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 were 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 exposed hydrogeological formations were recharged through precipitation by 0.329x109m3 and discharged by 0.317x109m3 during the study period. The karstic formations were recharged from precipitation by 45.0x106m3, while discharged from karstic springs by 47.88x106m3 of water. The discharge rate of major karstic spring ranges from 4.3 to 430 l/s and the discharge coefficient ranges from 0.004-0.026 day-1. The storage capacity of springs varies from 0.14-5.01x106m3 and the total discharged volume during the study period was 48.10x106m3. The groundwater budget of the valley-fill aquifer represents that during the study period recharged from different sources 0.266x109m3 and discharged 0.263x109m3 by all sources. The conceptual hydrogeological model of Niksar Valley simulates geological, hydroclimatic, hydrogeomorphologic, hydrostratigraphic, hydrogeological, and hydrologic field environments.

Keywords: Pontid, Anatolit, Karstic aquifer, Niksar Basin, Turkey. 1. Introduction tectonic setup with complicated aquifer systems ranges from confined to unconfined The Niksar Basin is selected to estimate the and from hard-rocks to karstic aquifers. groundwater budget and investigate Substantial efforts were made to estimate the hydrogeological features in this region. The hydrogeological framework characterization area is geographically situated between 36 43' and groundwater investigations of all 50” – 37 10' 25” East Longitude and 40 28' 25” hydrostratigraphic units. The exposed – 40 41' 50” North Latitude, as shown in Figure geological formations of similar 1. The geological, hydrogeological, and hydrogeological characteristics are groundwater investigations conducted on the qualitatively grouped as permeable, semi- basin spread over an area of 655 km2. The permeable, and impermeable units. Two investigations are part of the Ph.D. dissertation impermeable units comprised of schists, marl, submitted to the Department of Geological and mudstones. Three semipermeable units Engineering, Faculty of Engineering, Ankara comprised of conglomerate, sandstone, University, Turkey, (Aftab, 1989). The limestone with other intercalations. Two groundwater budget was estimated for the separate karstified limestone units studied valley aquifer that covers an area of 141 km2. separately as Lower and Upper Karstic Units. The Niksar Basin has a diverse geological and The karstification processes, recharge, and 69 discharge through karstic springs were September. To calculate the precipitation evaluated. The groundwater flow in different during the study period Thiessen Polygon and lithological units has directional anisotropic Isohyetal Precipitation maps were prepared behavior because of primary sedimentary, with data of seven existing and two new igneous, and metamorphic features, geological meteorological stations established in the structures, and hydrologic properties. The Niksar Basin. The cumulative yearly s t u d y c o m p r i s e s g e o l o g i c a l a n d precipitation for the study area is 555mm. hydrogeological factors affecting the vertical Precipitation for the budget period is 580mm and horizontal distribution of groundwater. and 571mm with Isohyetal and Polygon Inventory and periodical monitoring of all Methods respectively, the average of both surface and groundwater resources were methods is 576mm. The twenty-year averages carried out. The recharge and discharge zones minimum and maximum temperature of the of aquifers were evaluated, precipitation, study area ranges from 4.4-23.5oC in January surface and groundwater interaction, and and July respectively. The climogram of the groundwater fluctuations assessed. The fifty- study area based on twenty year's temperatures two groundwater springs having discharge and precipitation values represent January and more than1.0 l/s were periodically monitored. December are the rainy months. February to The recession curve analysis and reserve May and October-November are transitional, estimation of 9 major karstic springs were while June-September are dry months. The De calculated. The well-pumping and injection Martonne's (1942) aridity index (I) of 12.87 field tests have been performed. Groundwater represents that the study area embraced half- table and piezometric surface and equal dry to wet-weather. The climogram of the study variation maps were prepared. The area is presented in Figure 2a. The climatic groundwater budgets of the Quaternary aquifer pattern of the area may represent as C1 B2′ S covering the valley floor were appraised. b′4, accordingly characterize as dry-less-humid (C1), mesothermal (B2′), excess-water in 2. Hydroclimatology winter at mild-level (S), and near to areas effected by sea (b′4). The average humidity The twenty-year average precipitation value of the last twenty years is 55.3%. The amount of the study area is 547mm. The minimum humidity was 52% in March 1988 maximum precipitation of 164.5mm falls in and a maximum of 74% in December 1989. October and a minimum of 0.7mm in

Fig. 1. Location map of the study area. 70 Turc's method utilized to calculate yearly Etr soil moisture recharging. The Etpc was 742mm, which is 472mm and 86% of precipitation Etr 357mm, total precipitation 551mm, water (Turc, 1961). For the groundwater budget, the deficit 384mm, and water surplus 194mm. excess soil-water is 100%. Thornthwaite's Consequently, during the budget period, 65% (1948) climatic water balance model utilized of the total precipitation becomes part of the meteorological data to estimate monthly atmosphere through evapotranspiration. The potential evapotranspiration (Etpc) and soil moisture recharge during the same period computes actual evapotranspiration (Etr) and was up to 35% of precipitation. The monthly surface runoff. Precipitation and groundwater percolation and surface runoff are potential evapotranspiration graph have been 35% of the precipitation. The soil water budget prepared for the groundwater budget period of the area is presented in Table 1. from October 1986 to September 1987, Figure 2b. The graph representing, the periods of water surplus and deficit, soil moisture utilizing, and

Fig. 2. a) The climogram of study area based on twenty years average values, b) Precipitation and potential evapotranspiration graph, October 1986 to September 1987.

Table 1. The soil water budget of Niksar Basin.

71 3. Hydrogeomorphology shallow and rectangular drainage pattern is developed in areas where karstic rocks are The topography of the valley varies exposed. The gradient of prominent streams, between 250-400m from NW-SE parallel to the estimated with base profiles, accordingly based flow direction of the Kelkit River. The on the change in gradient streams was divided topographic slope of the valley is about 2%, the into the lower, middle, and upper parts. surrounding mountains are cut by streams with a slope range from 2-15%. The basin-low is The average temperature, precipitation, 250masl toward the western side of the valley and Kelkit River flow hydrographs of the last and the highest Kocatepe Mountain (M) twenty-year values have been prepared for 1,822masl in the NE. The hypsometric curve correlation. The average precipitation and represents the average topographic height of Kelkit River flow values have a direct the basin is 700masl. The oro-hydrographic relationship. In April, the cumulative maximum map of the basin prepared to demarcate ridges; precipitation was 39.6mm and the maximum drainage pattern, precipitation area, and water flow was 263.3m3/s, Figure 3. Similarly, in divide lines with topographic maps, 1/25,000. August, the minimum precipitation was 7.8mm In the eastern part, the ridges extended from E- accordingly flow drops to the minimum level of W following the tectonic pattern of the region, 13.3m3/s. The daily average flow values of the Seymen (1975). The prominent ridges are Kelkit River were utilized to calculate the base Taslica, Karacal M 1,808, and Alacal M flow during the study period. The flow 1,811masl. These ridges developed in Upper hydrographs of daily total precipitation and Jurassic-Lower Cretaceous limestone daily average flows were prepared to evaluate formations and form the water divide of the relationship between flow and floods. Canakci Stream (S). The northern slopes Schoeller's Hydrographycial Method was extended N-S, developed in the Jurassic and utilized to estimate the surface flow separated Eocene rocks, Golaga 1,502masl, is the highest from the base flow (Schoeller, 1962). ridges. The southern slopes extended in E-W Thereafter, the surface and groundwater flow of and were composed of metamorphic rocks of each area were analyzed. During the study the Jurassic - Eocene. Starting from west period, the Kelkit River flow to the basin was Kocadagi M 815, and Sumbulu M 1,011masl 5.57x109m3 and the base flow was are prominent ridges. 3.12x106m3. The flooding in the Kelkit River occurred from March to June. The highest The mountains surrounding the Niksar instantaneous flood of 905m3/s at Fatli Bridge Basin are covered with forests which are around was observed on April 16, 1968, and during the 53% of the landmass of the basin. The entire study, period 654m3/s on April 13, 1987, basinal plain is irrigated with the Kelkit River. (General Directorate of Electrical Affairs Etud The hydrography represents that structure, Administration of Turkey, EIE, 1968-1988). lithology, vegetation cover, and soil type affect The precipitation area of Canakci S is 93.8km2, the development of drainage pattern. Kelkit the discharge measurements were conducted 2- River flows in the center of the valley from S-N, 3 times per month at Kirec Bridge. The while all other streams flow towards the Kelkit maximum flow of 1.94x103m3/s was observed River. The Canakci S is the biggest stream on April 15, 1987, and a minimum of 0.13m3/s passing through Niksar Town from E-W. The on August 25, 1986. The cumulative yearly floor of the stream is deep and narrow and surface flow of Canakci S was 35.82x106m3 developed along Ladik-Niksar-Bereketli Fault and the base flow was 11.48x106m3. In central Zone, flows in magmatic rocks of the Eocene. part of the Niksar Valley, the groundwater table The drainage pattern of the associated streams is 0-2m deep in an area of about 50 km2. is rectangular and dendritic in nature. Toward General Directorate of State Hydraulic Works SW of Niksar, the Aybellini and Aksu Streams, of Turkey (DSI) maintaining a drainage system follow the Hanyeri-Gokcebet Fault Zone and of two-meter-deep to control the water table, flows from E-W. The valleys are narrow, V- (General Directorate of State Hydraulic Works shaped and the drainage patterns of associated of Turkey, 1968-1988). The drainage system streams are dendritic and rectangular. The having main and subsidiary surface drainage 72 canals. The water level fluctuates in the cumulative total discharge from drainage drainage canals have a similar pattern related to canals for the budget period was 129.9x106m3. the water level of Kelkit River. The minimum The surface and groundwater interaction and maximum discharge from drainage canals through the hydrographic relationship between was 3.21 and 6.15m3/s observed on October 2, precipitation, streamflow, and groundwater 1986, and October 13, 1987, respectively. The levels are presented in Figure 3.

Fig. 3. Surface and groundwater interactions: a) groundwater level fluctuations of the unconfined aquifer, discharge of artesian well and piezometric water levels, b) groundwater discharge of drainage canals, c) flood and base flow discharge of Canakci Stream, d) precipitation and flow of Kelkit River.

73 4. Hydrogeology well developed. These rocks are exposed and seen over a large area in the northeastern part of The Niksar Valley developed as a huge the hydrogeological map. The Impermeable tectonic depression, along the Kelkit River. The Basement is comprised of metamorphic series lithological units exposed on the northern and of Paleozoic, composed of schists, southern parts of the Kelkit River are grouped metaagglomerate, metachert, and metatuff. The as "Pontid" and "Anatolid" respectively, schists are impermeable, hydraulic (Blumenthal, 1950). These two groups of rocks conductivity developed in marbles, are studied separately and are separated from metaagglomerate, and metatuffs. The each other along the Kelkit River towards the southwestern part of the hydrogeological map east of the valley. The Pontid Group is is covered mostly with Semipermeable Unit composed of eleven lithological formations and (AG-3) and Impermeable Basement (GST). age-wise ranges from Paleozoic to Quaternary. The Semipermeable unit started with shale of The Anatolit Group is divided into four Lower Lutecian, interbedded with sandstone, formations ranges from Paleozoic to Cenozoic. conglomerate, and micritic limestone. The Paleozoic metamorphic rocks form the Sandstone, conglomerate, and limestone units basement in both groups, at Anatolid these have well-developed fracture systems. The rocks are exposed on a huge area while upper layers are composed of volcanic breccia comparatively cover a small area at Pontid. At of Upper Lutecian along-with andesitic lava Pontid on metamorphic schists due to tectonic flows. The hydrogeological map and activities of the Lower Jurassic a sedimentary stratigraphic column of the basin prepared succession of sandstone, conglomerate, and based on similar hydrogeological and synsedimentary volcanics were deposited. The hydrostratigraphic parameters are presented in limestone of the Upper Jurassic - Lower Figures 4 and 5 respectively. Cretaceous deposited above the succession. During Upper Cretaceous, the clayey limestone Hydrostratigraphy is related to the with andesitic tuff deposited. The marl and identification of rock units, lithological mudstone deposited in Upper Maastrichtian disparities, hydrogeological properties, and the detrital limestone deposited during the geomorphology, and structural and tectonic Upper Maastrichtian - Lower Palaeocene. The setups. Geologically exposed geological units flysch unconformably deposited in Lower comprised of clay, sand, gravel, conglomerate, Lutetian over the older formations. The Upper marl, shale, mudstone, sandstone, limestone, Lutetian andesitic and basaltic rocks cover the along-with many varieties of igneous and flysch. At Anatolid, the Palaeozoic schists metamorphic rocks. Altogether, geologically thrust over the Cretaceous Ophiolitic Series at f o u r t e e n d i v e r s e l i t h o l o g i c a l u n i t s the south of Niksar. The flysch of Lower hydrogeologically assembled into ten units Lutetian deposited unconformably over the Figure 4, and hydrostratigraphically into eight ophiolites and during Upper Lutetian volcanic groups, see Figure 5. The analysis is associated breccia covered all the older formations. The with the identification of potential groundwater exposed lithological and stratigraphic units bearing zones, recharge and discharge ranges, have different hydrogeological characteristics. evapotranspiration, surface, and groundwater The formations of similar hydrogeological interaction zones, and fluctuation in reserve characteristics are qualitatively grouped as estimations related to hydrostratigraphy. The permeable, semi-permeable, and impermeable d e s c r i p t i o n o f t h e l i t h o l o g i c a l a n d formations. hydrostratigraphic units are presented in the following paragraphs. Semipermeable Unit (AG-2) is composed of limestone of Lutetian and thin-bedded 4.1. Impermeable Basement (GST) mudstone, volcanogenic sandstone, and interbedded conglomerate lenses. The volcanic The metamorphic series of Paleozoic andesitic and basaltic lava flows, tuff, and forms the basement, which is composed of agglomerate of Upper Lutecian are s c h i s t s w i t h t h e i n t e r c a l a t i o n s o f impermeable but secondary permeability is metaagglomerate, metachert, and metatuff. The 74 marbles are exposed in the form of islands in the with marl and andesitic tuff. These limestones schists. Schists are impermeable while the show a lithologic change from micritic to secondary porosity and permeability developed biomicritic and detritic origins. An in metaagglomerate, metatuffs, and marbles. A interconnected diffused and conduit flow few springs with discharge, vary from 0.2 to 1.0 system developed together in both karstic L/s observed from metaagglomerate, metatuff, limestone units, (Atkinson and Hydrol, 1977; and marble formations. The marble is badly and Gunn et al. 1985). Both units investigated fractured and exposed in the form of small as a single aquifer from groundwater blocks and has a good aquifer characteristic. movement, recharge, and discharge point of Because of the limited exposure and recharging view. These limestone units have a well- area, the discharges took place from a few small developed karstic system. The hydrologic springs. Precipitation is the only source of properties vary with the variation of lithology recharge of the formation, the coefficient of and mode of deposition. Despite all lithological recharge varies from estimated as 1-2%. The variations, the secondary permeability is much narrow and deep dendritic drainage system greater than the primary. The groundwater indicates greater surface runoff. movement varies with the variation of lithology and groundwater-bearing rock properties. The 4.2. Semipermeable Unit (AG-1) lateral extent of the recharge area is quite significant, and precipitation is the only source The Jurassic rocks are composed of of recharge. The units discharge through conglomerate, sandstone; lave flows, tuff, marl, several small to large karstic springs. Surface and mudstone which are overlying the drainage is poorly developed. The infiltration basement rocks. The conglomerate is rate has varied, from place to place depending composed of volcanic pebbles and boulders upon structure, topography, soil cover, and which are semi-rounded and poorly sorted. solution cavities. The average value of the Sandstone is large-grained and poorly sorted. coefficient of permeability is 40%. Marl is hard and highly jointed and fractured while mudstone is thin-bedded. At places in this 4.4. Impermeable Unit (GSB) sedimentary series, lave flow is exposed. All units are well jointed, fractured, and faulted The Maastrichtian rocks form an structures. The precipitation is the only source impermeable unit, which is composed of thin- of recharge through a large surface area. bedded marl and mudstone. The marl and Recharge and discharge took place through mudstone are interbedded with thin bentonite secondary porosity and permeability. A few layers and thick tuff of blocky structure. springs having discharge, vary from 0.3-1.0 L/s Precipitation is the only source of recharge with are present in the formation. The recharge a considerably smaller area of recharge. The percentage varies as per change in lithology of coefficient of recharge estimated as varies from individual units. The estimated average 1-2 %t, no spring observed in this rock unit. coefficient of recharge for the Jurassic formation is 4%, which varies from low-high in 4.5. Permeable Upper Karstic Unit (GK-2) places where clayey to sandy units are exposed respectively. This karstic unit is of the Upper Maastrichtian-Lower Paleocene age and is 4.3. Permeable Lower Karstic Unit (GK-1) composed of detrital limestone. The limestone formation forms a separate karstic region of The Jurassic to Cretaceous age limestone good aquifer characteristics. The exposed formations has a well-developed karstic system recharge area through precipitation is small and in the area. The lower units of formation range the estimated coefficient of recharge is 40%. from Jurassic to Lower Cretaceous and are The unit discharges its water from springs that composed of necrotic, biomicritic, dismicritic, emerge by the contacts with other geological intrasparite, and detritic limestone. The upper formations. units are of the Upper Cretaceous age and are composed of clayey-limestone interbedded 75 4.6. Semipermeable Unit (AG-2) conglomerates of the Pliocene. These sediments are cropped out in the North-Western The unit composed of limestone of part of Niksar town. The gravels are well- Lutetian at the base and continues upward with rounded and poorly sorted. The unit is largely thin-bedded mudstone, volcanogenic composed of large clastic materials of the sandstone, and interbedded conglomerate Pliocene, at some places small size particles are lenses. Above these beds in the northern part of exceeded. The lithological logs of drilling wells the study area volcanic andesitic and basaltic and the geophysical studies represent that the lava flows and tuff and agglomerate of Upper Pliocene sediments are hundreds of meters Lutecian age covered a large area. At places, thick. These sediments are overlain by a 25- this unit is covered by organic clays of varying 70m thick alluvium sheet. These sediments thickness. The rock formations are have an aquifer of high yield; in the Northern impermeable but secondary permeability is and Southern slopes of Niksar Valley, a series of well developed. The surface drainage follows small and large alluvium cones are present. The the regional structure of the area. Many small alluvium aquifer recharges directly from and a few large springs are oozing out along the precipitation, Kelkit River, flood irrigation, and major fracture and fault systems. In the study perennial streams. The coefficient of recharge area, thin basaltic dykes of Miocene age cut the by precipitation is 30% and surface flows are volcanic and older formations. The basaltic 5%. The groundwater from the alluvial aquifer rocks are exposed in the form of huge blocks is drawn by digging wells, hand pumps, and with increased hydraulic conductivities. The drilled wells. The deepest well drilled in the famous excellent quality “Ayaz Spring” valley is 240m. In Niksar Valley fill material emerges from the basaltic formation. The after an average depth of 40m the gravel precipitation is the only source of recharge to a formation of Pliocene starts. The gravel, sand, large areal extent. The estimated coefficient of and clay beds are of varying thickness, color, recharge is 5.0-6.0%. particle size, and lithology. In between alluvial sediments, 2-23m thick a sheet of plastic clay is 4.7. Semipermeable Unit (AG-3) present. In the presence of the plastic clay layer, the alluvial aquifer is divided into a free surface The Semipermeable unit is started with and an artesian aquifer. In the Western part of thin-bedded shale of Lower Lutecian, which is Niksar Valley, the clay layer is thick and near to interbedded with sandstone, conglomerate, and the surface while towards the East thickness micritic limestone. Shale is impermeable, but gradually decreases and deep from the surface. sandstone, conglomerate, and limestone units The sediments above the clay bed have a greater have well-developed fracture and joint systems thickness towards the east. with increased secondary porosity and permeability. At the contact of shale and 5. Recharge and Discharge of sandstone, small discharging springs are Hydrogeological Units present. Some low discharging springs are In the study area, eight hydrogeological related to faults and fracture systems. The upper formations are exposed, almost all formations layers of this unit are composed of volcanic are naturally recharged through precipitation. breccias of Upper Lutecian. Within breccia, the These hydrogeological formations are andesitic lava flows are also present, which is discharged by natural groundwater through compact and fractured. The drainage system is small to large springs. For the study period, the deep dendritic. The precipitation is the only recharge through precipitation for each unit is source of recharge and the estimated coefficient calculated with the following relationship; I = A of recharge is 4.0-5.0%. x P x Ie. Where I is recharge through precipitation (m3), A is the area of 4.8. Permeable Unit (Qal) hydrogeologic units (m3), P is precipitation (m), and Ie is coefficient of recharge (%). The The Niksar Valley fill materials have coefficient of recharge varies from 0.01 to 0.40 started from the base with clayey-sandy depending on the lithological variations and gravels, loosely cemented sandstones, and primary and secondary porosity and 76 permeability of the hydrogeological units. The period, the total amount of recharge was exposed hydrogeological units covering an area 0 . 3 2 9 x 1 0 9 m 3 , a n d d i s c h a r g e w a s of 655 km2, the individual units range in area 0.317x109m3. The difference of 0.012x109m3 from 15 to 141 Km2. During the study period, between total recharge and discharge quantities these units' recharge amount with precipitation of all the hydrogeological formations is due to varies from 0.001-0.265x109m3. During the the average values, not considering the base same period, the discharge amount varies from flow of minor creaks, and evapotranspiration, 0.001-0.263x109m3m. During the study Table 2.

77 Fig. 5. Stratigraphic column of Niksar Basin showing the correlation between age, thickness, stratigraphy, lithology, and hydrogeologic units.

78 6. Hydrogeological Properties of Aquifers porosity. The pressing method of Castany (1963) was used to calculate the porosity of In the study area, the free surface and Quaternary loose sediments deposited by the artesian aquifers are developed in Quaternary Kelkit River and Pliocene sediments. The Alluvium and loose sediments of the Pliocene. samples were collected from a depth of 3-4 m, The general gradation trend of alluvial the porosity values are given in Table 3. The sediments has ranged from good to normal and porous box method of Schoeller (1967), the particles are different in size. The gradation utilized to calculate the permeability of of Pliocene sediments ranges from good to poor Quaternary sediments. The constant head and has great variation in particle diameter and permeameter was utilized to calculate the size distribution. The open space of filters used permeability of Pliocene sediments. The in installed tubewells in Niksar valley ranged pumping tests were conducted to calculate the T from 0.5-2.0mm (d40) as per intercepted and K values by Theis (1935) and, Jacob (1947) formations, Table 3. The porosity, hydraulic methods, and the aquifer recovery test was conductivity (K), transmissivity (T), and analyzed by assumptions of Houpert-Pouchan; storage coefficient were calculated in the lab de Marsily, (1986), is presented in Table 4. The with aquifer sediment samples and in the field reserve constant and the effective radius of the by pumping and injection or slug tests. The pumping wells were not calculated due to the secondary porosity is well developed in almost absence of piezometers. The Slug Tests were all the exposed formations, which is related to conducted in 13 shallow auger-hole wells to fractures, joints, cracks, bedding planes, and calculate the T, K, and storativity (S) values, faults. The solution cavities in limestone (Bower, 1989). The results of the slug tests are formations play a dominant role in secondary presented in Table 5.

Table 2. Recharge and discharge quantities of hydrogeological units.

Table 3. Grain size, porosity, and permeability of hydrogeological units.

79 Table 4. Results of well-pumping test analysis.

Table 5. Results of slug test analysis.

7. Hydraulic Head Conditions the artificial drainage canal system. The fluctuation caused by precipitation varies from To monitor the fluctuations in the place to place depends on topography, the groundwater table a network of 95 groundwater thickness of the vadose zone, hydraulic measuring points was established in the basin, conductivity, distance from permeable and Table 6. Continuous monitoring with a fixed impermeable boundaries, and structural interval of 5-10 days has been carried out. The elements including faults, fractures, folds, major hydrologic factors which affect the short bedding planes, dip, strikes, and lithology of and long-term fluctuation of groundwater formations. In the Northern part of the Kelkit levels are precipitation, surface runoff, River, the groundwater level falls from irrigation water, pumpage from wells, February-April, and from August-October the evaporation, transpiration, and discharge from groundwater reached its maximum level, the 80 the water level fluctuation is related to pattern of fluctuation in all parts of the confined precipitation. In the Southern part of Kelkit aquifer, the maximum and minimum level River, the minimum water level was observed observed in May and March respectively. The during the months of November-January and hydraulic gradient of the potentiometric surface maximum during May-July. The groundwater in June 1987 was 1.2 x10-3 to 6.5x10-4. The level fluctuates under the influence of the flow surface and groundwater interaction via a level of the Kelkit River. The wells drilled in comparison between precipitations, discharge Upper Jurassic-Lower Cretaceous limestone of streams, drainage canals, artesian well, and formations represent a groundwater level rises groundwater level fluctuations in the alluvium and fall quite rapidly. The eight-meter wells are presented in Figure 3. variations in groundwater level are due to a well-developed karstic system. In the central 8. Groundwater Table Maps part of the aquifer, the groundwater level fluctuations represent an irregular pattern. In Niksar Valley is comprised of confined the said area the precipitation, irrigation water, and unconfined aquifer systems developed evapotranspiration, and flow through artificial under suitable hydrodynamic conditions. The drainage canals affect the groundwater levels. water table maps of the unconfined aquifer and Comparison between precipitation, Kelkit potentiometric surface of the confined aquifers River flow, discharge of artesian well, and were prepared for the highest and lowest groundwater level fluctuations are presented in periods of the water table. The water table map Figure 3. The groundwater table is 0-2m deep in of the unconfined aquifer was prepared with the an area of about 50 km2 at the central part of the help of 85 monitoring points; among them, 13 basin, Figure 5. The General Directorate of are dug wells, 63 piezometers, 9 drilled wells, State Hydraulic Works of Turkey maintaining a and 10 artesian wells. The highest level of drainage system of two-meter-deep to control groundwater table for unconfined aquifer was the water table in the valley (DSI,1968-1988). prepared for June 1987, Figure 6a. Kelkit River The drainage system is comprised of main and and drainage canals affect the groundwater subsidiary surface drainage canals. The water levels and flow directions. The dominant level fluctuates in the drainage canals have a groundwater flow direction is towards NW. The similar pattern with the water level of Kelkit Kelkit River round the year feeds the aquifer River. The minimum and maximum discharge from the eastern side. While from the western from drainage canals was 3.21 and 6.15m3/s side round the year, the drainage canals and observed on October 2, 1986, and October 13, unconfined aquifer directly feed the Kelkit 1987, respectively. The Total discharge from River. The groundwater flow direction and the drainage canals for the budget period was hydraulic gradient is diverse from place to place 129.9x106m3. in the valley. The hydraulic gradient ranges between 2.0-3.0x10-3. The maximum rise in the water table of the unconfined aquifer was observed in June 1987 The lowest period groundwater table map of the and the minimum water level in December unconfined aquifer was prepared for December 1986. The hydraulic gradient is different from 1987, presented in Figure 6b. It represents that region to region and ranged from 1.6x10-3 to the general groundwater flow direction is 2.5x10-2. The difference in water level ranged almost the same everywhere as in the maximum from 0.01-9.4m. The artesian wells present in level groundwater map. The equal groundwater the central part of the Niksar Basin toward the flow contour lines become wider. The western side of the Kelkit River. The hydraulic minimum and maximum groundwater levels head variation of confined aquifer measured fall from 3.8-9.4m. The groundwater level of from artesian wells, the potentiometric surface the unconfined aquifer was highest in June varies from 0.02-0.40m above the ground 1987 and lowest during December 1986. Based surface of the valley. The potentiometric levels on the difference of both levels, the equal vary with the variation in precipitation and change in groundwater level map prepared, water level of the Kelkit River. The Figure 6c. The monitored minimum difference potentiometric surface represents a similar in both levels was 0.01m at piezometer No. 61. 81 The maximum difference was recorded at 9.4m Ten artesian wells existed in the valley at drilled well No. 4684. The groundwater level drilled by DSI. The piezometric surface maps change in the western and central parts of the of the confined aquifer developed in the valley valley is less than 1.0m. From the east towards were drawn with the help of artesian wells. The the northern and southern parts, the difference discharge of the artesian wells and piezometric in groundwater level is 1-4m. Towards the east, surface regularly monitored during the study it varies from 4.0-7.0m and further east it's more period for correlation, presented in Figure 3. than 9.0m. The highest piezometric surface level map for June 1987 has been prepared, shown in Figure The Quaternary and Pliocene deposits are 7a. The piezometric surface contour lines are predominantly recharged by the Kelkit River very smooth and parallel to each other and rather than precipitation. The alluvium increasing from Northward to Southward. The naturally discharges to the Kelkit River and lowest piezometric surface level of the artificial discharge took place through drainage confined aquifer was observed in December canals and pumping wells. The aquifer 1986, the map is presented in Figure 7b. The recharged with different sources during the groundwater flow direction of the confined study period. The difference in maximum and aquifer and patter of the piezometric contour minimum groundwater table maps between lines remains the same during both the highest June 1987 and December 1986 was calculated and lowest periods. The groundwater flow with the relationship; V = S x A x Δh, and ΣV = direction also remains the same from V1 + V2 + V3 + V4. Where V is the aquifer's Southward to Northward parallel to the flow of recharge volume in m3. A is an area of equal Kelkit River. The difference in the highest and change in water level m2, Δh is the equal lowest period of piezometric surfaces varies change in quantity m. The n is porosity, an between 1.10-2.20m observed at drilled average of 30%. V1, V2, V3, V4, are equal artesian well numbers 86 and 1611. The water changed in different areas of the aquifer hydraulic gradient of the piezometric surface in m3. The difference in groundwater level during 1987 in the eastern region ranges from during the lowest and highest periods of study 1.2x10-3 to 6.5x10-4, and in the western region ranges from 0 to >7m. The equal change in increased to 2.4x10-3. groundwater level at region h1 = 0 - 1m, h2 = 1 - 4m, h3 = 4 - 7m and h4 = > 7m, Figure 6c. The 9. Karstification and Karstic Springs calculated volume of equal change in water level at different areas of the aquifer are as The Jurassic-Cretaceous limestone follows; V1 = 0.019x109 m3; V2 = 0.022x109 formations have a well-developed karstic m3; V3 = 0.019x109 m3; and V4 = 0.079x109 system in the area. Interconnected diffused and m3. conduit flow system developed together in karstic limestones. The karstification, The total volume of water recharged to the groundwater movement, recharge, and aquifer during the study period was V = discharge studies were conducted, (Aftab et al., 0.139x109 m3. For the study period, equal 1997). The groundwater movement mainly change in the groundwater table map is depends on variation in lithology and hydraulic prepared by the values of the difference properties. The lateral extent of the recharge between the two lowest periods of the area is quite significant, and precipitation is the unconfined aquifer of the valley. The only source of recharge. The units discharge groundwater table equal change map based on a through several small to large karstic springs. difference in values of December 1986 and The infiltration rate has varied, from place to February 1988, Figure 6d. The groundwater place depending upon structure, topography, table was high in February 1988 as compared to soil cover, and solution cavities. To analyze the December 1986, the rise varies between 0-2 m karstification process, geochemical analysis of in different parts of the valley. During the same a few rock samples from different localities was time, the total groundwater addition (∆s) in the analyzed, (Taskin, 1977). The analysis aquifer was 0.054x109m3. represents that despite all lithological variations the CaO quantities vary between 82 49.3-55.6%. While the CaCO3 quantity in all rich carbonic acid rainwater to dissolve and samples ranges from 88.0-99.3%. The analysis wider solution cavities. It's technically represents that the excessive amount of CaCO3 confirmed that in well-developed karstic in limestone formations helps to react fast with regions, the CaCO3 is more than 90%.

Fig. 6. Groundwater table contour maps of unconfined aquifer (masl); a) highest level contour map of June 1987, b) lowest level contour map at December 1986, c) groundwater-level-change-map between highest and lowest levels, d) groundwater-level-change-map between two lowest levels December1986 and February 1988; for legend see Figure 5. 83 Fig. 7. Potentiometric surface maps of confined aquifer; a) during highest level potentiometric surface map June 1987; b) lowest level potentiometric surface map December 1986.

Several karstic and non-karstic springs emerge in depressions and major artificial emerge from karstic and hard rocks located in drainage canals. The geological cross-section the study area. The inventory and monitoring of and weekly discharge hydrographs of nine 51 springs having a discharge of more than 1.0 major karstic springs were analyzed L/s were conducted during the study period. systematically. The discharge coefficient, The karstic springs of low to high discharge are reserve capacity, and discharge volume were emerging from limestone formations of evaluated by Castany's relationship, (Castany, Jurassic-Lower Cretaceous, Upper Cretaceous, 1963). q = qo e- α(t-to), where q = t times and from Upper Cretaceous-Lower Paleocene. discharge in m3/s, qo = to times discharge or The discharge of the karstic springs varies from start at reserve discharge in m3/s. e = 2.718 or ln 1.0-500 L/s. Many other small springs are = 0.434, α = discharge coefficient in days. The emerging from different geological formations reserve estimation of karstic springs above the with a variation in discharge from 0.5-5.0 L/s. point of discharge, discharge coefficient, the The majority of these springs are originating volume of the potential reserve or reserve through faults and are classified as fault capacity (V) calculated with the Maillet springs. The andesitic and basaltic formations integration as follows (Maillet, 1905); of Eocene are severely fractured and faulted from where emerging springs are fracture springs. The small springs emerge from bedding planes and formation contacts of Paleozoic schists comprised of sedimentary In the equation to and t used to calculate series and mudstone of Upper Cretaceous, and the difference of total spring discharge. flysh series of Eocene. The valley springs Yolkonak-II spring in one of the largest springs 84 originates at the contact of valley alluvium and this regime, the spring's storage capacity V = Permeable Lower Karstic Unit (GK-1). The 2.79x106 m3. The total spring discharge unit is comprised of Jurassic to Cretaceous age volume during the entire study period was formations composed of biomicritic, 8.61x106 m3, this quantity is the sum of dismicritic, and intrasparite limestone having a discharges of two actual discharge regimes and well-developed karstic system. Two recession an increase in flow due to recharges. Yolkonak- periods encountered during the study period, in II Spring analysis, schematic geological x- both hydrodynamic regimes of karst aquifers section, origin, recession curves dynamics, and were analyzed. The first discharge regime of discharge hydrograph is presented in Figure 8. spring comprised of 145 days and discharge The minimum to the maximum discharge of varies between q01 = 240 L/s to q1 = 68. During nine major karstic springs ranges from 4.3 to the same regime discharge coefficient α = 430 L/s, discharge coefficient from 0.0009 to 0.00874 day-1, the actual discharge was q = qo 0.0255 day-1, storage capacity from 0.14 to e-0.0087t, reserve's storage capacity V = 5.01x106m3, and discharge volume varies 1.7x106 m3. The second real discharge regime from 0.27 to 8.61x106m3. During the study of the same spring comprised 115 days, period, the total storage capacity and discharge whereby q02 = 445 L/s and q2 = 17 L/s. The volume of all nine springs were 14.78 and 48.08 discharge coefficient α = 0.0085 day-1, and the x106m3 respectively. The hydraulic properties actual discharge was q = qo e-0.0085t. During of springs are given in Table 6.

Fig. 8. Yolkonak-II Spring analysis; a) geological x-section, b) recession curves dynamics, c) discharge hydrograph; for legend see Figure 5.

85 10. Groundwater Budget on hydrogeological parameters prepared with realistic field conditions of Niksar Valley. The The groundwater budget for the m o d e l s i g n i f i e s h y d r o c l i m a t i c , Quaternary and Pliocene aquifer spread over an hydrogeomorphologic, hydrostratigraphic, area of 141 Km2 were appraised, (Canik, and hydrogeological, and hydrologic data to define Aftab, (1990). The groundwater budget for the the physical parameters of water-bearing period of October 1986 to September 1987 was formations, (Aftab, 2017a, b). The model- calculated by measuring all elements of oriented northwest-southeast direction along recharge and discharge to and from an the cross-sections A-B of the hydrogeological unconfined aquifer. To calculate the map of the Niksar Basin Figure 5, and enlarged groundwater budget general budget equation of along cross-section X-Y. The model represents Schoeller, and Canik was utilized (Schoeller, geological, lithological, tectonic, and 1967; and Canik, 1971). The groundwater climatical descriptions along-with surface and budget equation in its simplest form may be subsurface hydrogeologic components of written as; confined and unconfined aquifers, Figure 10. The important input parameters of the model P + V'r1 + V'r2 + V'n + V'a = Etr + Vr + Vnr + Δs are temperature, precipitation, humidity, + Va1 +Va2 thermal index, wind speed, and direction with associated groundwater recharge. The Where P= Precipitation, V'r1= Recharge from parameters related to land cover are topsoil Kelkit river, V'r2 = Recharge from Canakci depth, porosity, hydraulic conductivity, and stream, V'n = Recharge from other aquifers, V'a residual water content. These parameters are = Recharge from irrigation waters, Etr = important for infiltration and groundwater Evapotranspiration, Vr = Surface runoff, Vnr = movement. The model also represents Discharge to Kelkit river, Δs = Addition in the hydraulic-head conditions, aquifer storability, aquifer reserve, Va1 = Discharge by drainage transmissivity, and hydraulic conductivity. The canals, Va2 = Water withdrawal from the actual evapotranspiration, surface runoff, aquifer by pumpage. During the budget period, subsurface flow, and groundwater discharge the aquifer received a maximum quantity of among different sources are resulting water from the Kelkit River which is parameters. The conceptual model represents 0.171x109m3 and 64.3% of all recharge all physical processes observed through field quantities. Aquifer discharge maximum investigations. quantity through drainage canals 0.125x109m3 which is 47.5% of total discharges. The aquifer The conceptual hydrogeological model of received a total quantity of 0.266x109m3 of Niksar Basin maybe translates into a GIS-based water and discharged 0.263x109m3 of water three-dimensional calibrated numerical through all sources. The difference of groundwater flow model of the basin. By 0.003x109m3 is due to average values of incorporating published and unpublished recharge and discharge parameters measuring additional study data, the model may errors, and unmeasured parameters, etc. The interpolate geological and tectonic recharge and discharge elements along-with relationships with the flow system of basinal percentage values are presented in Figure 9. aquifers. The model may have utilized in the future for decision support and studies on the 11. Conceptual Hydrogeological Model impact of climate change on groundwater balance in time and space. The climatical T h e d e t a i l e d r e g i o n a l - s c a l e effects on karstification processes and the flow h y d r o g e o l o g i c a l a n d g r o u n d w a t e r patterns of Niksar Karstic springs may also investigations of Niksar Basin represent a interpolate and envision. complex hydrogeological system. The significance of topography, geology, and tectonics of the area premeditated and correlated with the regional flow parameters of the study area. The conceptual model is based 86 Fig. 9. Recharge and discharge elements of groundwater budget of Quaternary Aquifer.

Fig. 10. Conceptual hydrogeological model of Niksar Valley; for legend see Figure 5.

11. Conclusion among geological formations. The average yearly precipitation 551mm, Etpc 742mm, Etr T h e P a l e o z o i c S c h i s t s f r o m a n 357mm, water deficit 384mm, and water impermeable basement in the study area, while surplus 194mm. About 65% of precipitation the isles of marble form permeable zones. The return back to the atmosphere through limestone formations of Upper Jurassic-Lower evapotranspiration. The soil moisture recharge Cretaceous and Upper Maastrichtian-Lower was 35% of precipitation, the surface runoff is Paleocene form important karstic aquifers GK- 28% of precipitation. The groundwater flow 1 and GK-2 respectively. The marl and directions of confined and unconfined aquifers mudstone of Upper Maastrichtian form are different from region to region, but in the significant impermeable boundaries GSB eastern and central regions, it's from southeast 87 to northwest. The hydraulic gradient of Author's Contribution confined and unconfined aquifers are diverse from place to place and vary from season to Syed Mobasher Aftab conducted this season; ranges between 1.2x10-3 to 6.5x10-4, research work as part of the Ph.D. dissertation and from 2.0 to 3.0x10-3, respectively. Induced entitled, “Hydrogeological Investigations of groundwater resources and the interaction Niksar (Tokat) Basin, Turkey”, submitted to the between surface and groundwater-dominated Department of Geological Engineering, by the flow of Kelkit River. Kelkit River Science Faculty, Ankara University, Turkey. d i s c h a rg e d 5 . 5 7 x 1 0 9 m 3 , b a s e f l o w 3.12x106m3, Canakci Stream discharged References 35.82x106m3, base flow 11.48x106m3, and Aftab, S M, 1989. Hydrogeological discharged from artificial drainage canals Investigations of Niksar (TOKAT), Valley, 0 . 2 2 1 x 1 0 9 m 3 o f w a t e r. T h e e i g h t Turkey. Unpublished PhD Dissertation, hydrogeological formations that exposed on an (Turkish), Ankara University, Ankara, area of 655 km2 recharged through Turkey, pp.324. precipitation 0.329x109m3 and discharged Aftab, S M, 2017a. Hydrogeology of Niksar 0.317x109m3 during the study period. The Basin, Tokat, Turkey. GSA Annual karstic formations recharged from precipitation Meeting in Seattle, Washington, USA - 49.92x106m3, while discharged from karstic Paper No. 121-9, Abstract. Geological springs 48.08x106m3. The discharge Society of America Abstracts with coefficient of nine karstic springs ranges from P r o g r a m s . 4 9 ( 6 ) d o i : 0.0043-0.01 day-1, and storage capacity above 10.1130/abs/2017AM-29989, discharging point varies from 0.14-5.0x106m3. Aftab, S M, 2017b. Hydrogeology of Niksar The groundwater budget represents that aquifer Basin, Tokat, Turkey. GSA Annual recharged from different sources 0.266x109m3 Meeting in Seattle, Washington, USA - of water and discharged 0.263x109m3 through Paper No. 121-9. Presentation, Handouts all sources. The conceptual hydrogeological PDF. model of the Niksar Valley signifies Aftab, S M, AFSIN, M., and CELIK, M., 1997. hydroclimatic, hydrogeomorphologic, Hydrogeological Study and Discharge hydrostratigraphic, and hydrogeological field Features of the Niksar Karst Springs, environments. The model characterizes Turkey. The Arabian Journal for Science geological, tectonic, climatical, surface, and and Engineering. Dehran, Saudi Arabia. subsurface hydrogeologic components of 22(2A), 131-144. confined and unconfined aquifers. Atkinson, T. C., Hydrol, J., 1977. Diffuse Flow and Conduit Flow in Limestone Terrain in Acknowledgment Mendip Hills, Somerset, Great Britain, 35, 93-100. The Higher Education Commission of Blumenthal, M M., 1950. Orta ve Asagi Pakistan financed to present the study at the Yesilirmak Bolgelerinin (Tokat, Amasya, GSA Annual Meeting held on October 22-25, Havza, , Niksar) Jeolojisi Hakkinda. 2017 in Seattle, Washington, USA (Aftab, M.T.A. Seri D, No.4, (Turkish) Ankara, 2017a, b). This classical study is part of Ph.D. Turkey. dissertation entitled, “Hydrogeological Bouwer, H. H., 1989. The Bower and Rice slug Investigations of Niksar (Tokat) Basin, Turkey” test – An update. Ground Water, 27 (3), submitted to the Science Faculty of Ankara 304-309. University, Turkey, (Aftab, 1989). The Canik, B., 1971. Yeralti Suya Rilaneosu, MTA hydrogeological investigations were conducted dergisi No. 76, (Turkish), Ankara, Turkey. under the supervision of late Professor Dr. Baki Canik, B., and Aftab S M., (1990). Groundwater Canik. The purpose of this publication is to Budget of Niksar (Tokat) Valley, Turkey. acknowledge the professional excellence of “Communication”, Journal of Science Professor Canik as a pioneer in the field of Faculty of Ankara University, (Turkish), Hydrogeology. Turkey, 8, 1-11. Castany G., 1963. Traité pratique des eaux 88 souterraines. Dunod, Paris, 657. Schoeller, H., 1962. Les eaus souterraines. De Marsily, Ghislain, 1986. Quantitative Hydrologie dynamique et chimique; hydrogeology Groundwater hydrology for recharge, exploitation et evaluation des engineers: New York, Academic Press, resources, 1, 642. Inc., pp. 440. Schoeller, H., 1967. Methods Pour Obtenir Le De Martonne, E., 1942. Nouvelle carte mondiale Bilan Des Eaux Souterrainex. Extrait de de l'indice d'aridité. Annales de Géographie “Eaux Souterraines” Assemblee Generate 51, 242–250 (in French). de Berne, Louvain, Belgium. General Directorate of Electrical Affairs Etud Seymen, I., 1975. 'The Tectonic Features of the Administration of Turkey (EIE), 1968- North Anatolian Fault Zone in Kelkit 1988.The daily discharge rates data of Valley”, Ph. D. Thesis, ITU Faculty of Kelkit River. Mines, Istanbul, (Turkish), Turkey. pp. General Directorate of State Hydraulic Works of 192. Turkey (DSI), and Ministry of Agriculture, TASKIN. C., 1977. Tokat ili Niksar ilce Merkezi Forestry General Directorate of cevresindecimento ve toz kirec hammade Meteorology Affairs (DMI), 1968-1988. olanaklarinin ararstirilmasi hakinda repor. The monthly drainage, precipitation, M.T.A. Der. No. 6004. Ankara. temperature and wind speed at different Theis, C. V., 1935. The relation between the meteorological stations in and around lowering of the piezometric surface and the Niksar. rate and duration of discharge of a well Gunn, J., G. Gunay & A. I. Johnson, 1985. A using ground‐water storage. Eos, Conceptual Model for Conduit Flow Transactions American Geophysical Dominated Karst Aquifers”, in Karst Water Union, 16(2), 519-524. Resources. Proc. Ankara Symp. IAHS, Thornthwaite, C. W., 1948. An approach toward Publication, 161, 587-596. a rational classification of climate. Jacob, C.E., 1947. Drawdown test to determine Geographical review, 38(1), 55-94. effective radius of artesian well, Trans. Turc, L., 1961. Water requirements assessment American Society of Civil Engineers, 112, of irrigation, potential evapotranspiration: , 1047-1064. Simplified and updated climatic formula. Maillet, E., 1905. Essais d'hydraulique Annales Agronomiques, 12, 13-49 souterraine et fluviale. Librairie Sci., A. Hermann, Paris, 218. Schoeller H., 1967. Quantitative evaluation of groundwater resources. In: Methods and Techniques of Groundwater Investigation and Dev. UN Water Resources Series 33: pp. 21-44.

89