International Journal of Geo-Information Article Identification of Groundwater Potential Zones Using GIS and Multi-Criteria Decision-Making Techniques: A Case Study Upper Coruh River Basin (NE Turkey) Ümit Yıldırım Department of Interior Architecture and Environmental Designing, Faculty of Arts and Designing, Bâberti Settlement, Bayburt University, 69000 Bayburt, Turkey; [email protected]; Tel.: +90-(458)-211-1152 (ext. 2209) Abstract: In this study, geographic information system (GIS)-based, analytic hierarchy process (AHP) techniques were used to identify groundwater potential zones to provide insight to decisionmakers and local authorities for present and future planning. Ten different geo-environmental factors, such as slope, topographic wetness index, geomorphology, drainage density, lithology, lineament density, rainfall, soil type, soil thickness, and land-use classes were selected as the decision criteria, and related GIS tools were used for creating, analysing and standardising the layers. The final groundwater potential zones map was delineated, using the weighted linear combination (WLC) aggregation method. The map was spatially classified into very high potential, high potential, moderate potential, low potential, and very low potential. The results showed that 21.5% of the basin area is characterised by high to very high groundwater potential. In comparison, the very low to low groundwater potential occupies 57.15%, and the moderate groundwater potential covers 21.4% of the basin area. Citation: Yıldırım, Ü. Identification of Groundwater Potential Zones Finally, the GWPZs map was investigated to validate the model, using discharges and depth to Using GIS and Multi-Criteria groundwater data related to 22 wells scattered over the basin. The validation results showed that Decision-Making Techniques: A Case GWPZs classes strongly overlap with the well discharges and groundwater depth located in the Study Upper Coruh River Basin given area. (NE Turkey). ISPRS Int. J. Geo-Inf. 2021, 10, 396. https://doi.org/ Keywords: remote sensing; analytic hierarchy processes; geographic information system; sustainable 10.3390/ijgi10060396 groundwater management; multi-criteria decision making Academic Editors: Raffaele Albano and Wolfgang Kainz 1. Introduction Received: 30 March 2021 Water is of vital importance to living life and plays an essential role in determining Accepted: 5 June 2021 Published: 8 June 2021 countries’ socio-economic levels. Surface waters (rivers, lakes, etc.) and groundwater constitute the natural, freshwater resources on earth. The changing climatic conditions, increasing human population, and changing land-use conditions, especially growth urban- Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in isation, put increasing pressure on these resources. 3 published maps and institutional affil- In Turkey, the amount of available usable water per person was 1652 m in 2000, 3 3 iations. which decreased to 1544 m in 2009 and 1346 m in 2020 [1]. As a result of the climate projections (RCP 4.5 and RCP 8.5) applied for the Coruh River Basin, which is one of the 25 major river basins of Turkey, towards 2100, it is predicted that the temperatures will increase by 0.4–6.1 ◦C, rainfall will decrease by 10%, and, therefore, the groundwater reserve will decrease by 0–7% [2]. The discharge rate of the Coruh River will reduce by Copyright: © 2021 by the author. 25% [2]. These tendencies reveal the increased pressure on the available water resources in Licensee MDPI, Basel, Switzerland. This article is an open access article the Coruh River Basin and the whole of Turkey. distributed under the terms and Groundwater is one of the most critical resources for drinking and irrigation. The total 6 3 conditions of the Creative Commons amount of water withdrawal in the Coruh River Basin is 46 × 10 m /yr, of which 54% Attribution (CC BY) license (https:// is used for agriculture and 44% for domestic use [3]. In the upper parts of the Coruh creativecommons.org/licenses/by/ River Basin, the headwater area, industrial areas in the region are minimal, due to the 4.0/). difficulty of transportations to the region. The people of the region earn their living from ISPRS Int. J. Geo-Inf. 2021, 10, 396. https://doi.org/10.3390/ijgi10060396 https://www.mdpi.com/journal/ijgi ISPRS Int. J. Geo-Inf. 2021, 10, 396 2 of 23 agriculture and animal husbandry, due to the restriction of job opportunities. Considering such an enormous amount of groundwater use for agricultural activity, the importance of sustainable groundwater management and planning in the basin is understood more clearly. Overabundant water withdrawal from the aquifer would damage the region en- vironmentally and economically [4]. Therefore, the groundwater potential zones should be determined by focusing on convenient water management. Traditional methods used in groundwater potential assessment studies, such as geophysical, hydrogeological and drilling techniques, are quite costly and time-consuming in spacious areas [5–7]. The de- lineation of potential groundwater zones has become more accessible and more effortless with geospatial methods, which have been widely used in recent years [8–11]. The use of remote sensing and GIS-based multi-criteria decision analysis methods (MCDM) to investigate groundwater potential zones has extremely increased over the last several decades [12–19] due to the rapid, precise and cost-effective investigation of surface and subsurface water over large areas. Several MCDM applications, such as multi-attribute utility theory (MAUT) [20], analytic hierarchy process (AHP) [18,19,21], fuzzy set theory (FST) [22,23], multi influencing factor (MIF) [24,25], data envelopment analysis (DEA) [26], ELECTRE [27], TOPSIS [28,29], and PROMETHEE [30] received much attention due to their potential use in water management assessments. Among these methods, the AHP tech- nique [31] is much more common for the GWPZs delineation, as it integrates to GIS [32–35]. It was developed by hierarchically planning, evaluating and weighting the criteria based on similar studies and expert opinions [31]. In the groundwater potential zone determination studies, many factors (e.g., lithology, soil texture, land-use land classes, drainage density, lineament density, geomorphology, slope, topographic wetness index, soil depth, rainfall, distance to the river, water table depth, and digital elevation model) related to groundwater storage based on geologic, hydrologic, hydrogeological, meteorological and terrain features were used as decision criteria for the multi-criteria decision analysis [25,36–39]. The MCDM-integrated GIS analysis for the groundwater potential index can provide the information needed for decision making more clearly and makes it easier for decision- makers to make more accurate and quicker choices during the decision phase. This study aims to determine the groundwater potential zones in the Upper Coruh River Basin (UCRB) under the pressure of changing land use (especially urbanisation) in line with changing climatic conditions and increasing living needs, using the GIS-based MCDM technique. In this way, decisionmakers will be provided with foresight and support in water and land use management for future planning. In the study, ten different decision criteria (i.e., slope, topographic wetness index, geomorphology, drainage density, lithology, lineament density, rainfall, soil type, soil thickness, and land-use classes) controlling groundwater storage were utilised for the assessment of the groundwater potential index. 2. Materials and Methods 2.1. Basin Characteristics The Coruh River Basin is one of the 25 major river basins of Turkey. The Upper Coruh River Basin (UCRB) is the headwater basin in the Coruh River, and it covers an area of about 4000 km2 between latitudes 39◦54030.70” to 40◦31016.34” N and longitudes 39◦40006.43” to 41◦10044.14” E. A large part of UCRB is located in the Bayburt province (73.8%), and the remaining part lies in the Erzurum (21.4%), Gümü¸shane(2.7%) and Erzincan (2.1%) province, NE Turkey (Figure1). ISPRS Int. J. Geo-Inf. 2021, 10, 396 3 of 23 ISPRS Int. J. Geo-Inf. 2021, 10, x FOR PEER REVIEW 3 of 23 Figure 1. The Coruh River Basin location (the boundary is shown in dark blue colour) in the part of Figure 1. The Coruh River Basin location (the boundary is shown in dark blue colour) in the part of Northern Turkey and the extent of the Upper Coruh River Basin (UCRB) and the gauging station’s Northernlocation. Provincial Turkey and boundaries the extent are ofshown the Upperin grey Coruhcolour. River Basin (UCRB) and the gauging station’s location. Provincial boundaries are shown in grey colour. The UCRB ranges from 1486 m to 3265 m, with slopes ranging from 0° to 64° (Figure ◦ ◦ 2a,b).The The UCRB basic characteristics ranges from 1486 for the m toUCRB 3265 are m, withpresented slopes in ranging Table 1, fromand the 0 toones 64 about(Figure 2a,b). Thethe current basic characteristics GWPZs modellingfor theare given UCRB in are Figure presented 2a‒f. The in Coruh Table River,1, and which the ones has the about the currentthird-highest GWPZs runoff modelling coefficients are of giventhe 25 ma injor Figure river2 a–f.basins The in Turkey, Coruh originates River, which in thehas the third-highestMescit Mountains runoff in the coefficients Bayburt province. of the The 25 majorriver flows river into basins the Black in Turkey, Sea after originates crossing in the Mescitthrough Mountains the Bayburt, in Erzurum,