Selection of a dam site by using AHP and VIKOR: The Sakarya Basin

1 Introduction

Dams play a significant role in the management of water resources, energy production, and flood protection, among many other important areas [1]. Especially in earthquake-prone areas, dam site selection involves many critical factors regarding structural safety, soil conditions, emergency management, and environmental impacts. Therefore, dam site selection should be carried out through a detailed analysis and evaluation process. Multi-criteria decision-making (MCDM) methods aim to systematically manage this process and reach an optimal solution among numerous alternatives evaluated based on different criteria [2]. The choice of the method varies depending on the problem and the needs [3,4,5]. MCDM methods are often encountered in studies where they are used alone as well as in combination with multiple methods [6,7].

In dam site selection, many criteria should be considered within environmental, economic, and social frameworks [8]. In the evaluation of water resource quality, the effectiveness of methods such as the integration of self-organizing maps and geographic information system techniques has been demonstrated in the literature [9]. It has been assessed that such approaches are also beneficial in the analysis of environmental factors in dam site selection.

Accurately determining the effectiveness of the criteria to be considered is critically important. The evaluation criteria have been obtained from similar studies in the literature [10,11,12] and from the expert opinions of seven academics working in the fields of water resources and earthquake engineering at Kocaeli, Yalova, and Altınbaş Universities. The evaluation results have been included in the decision-making process by analyzing them with mode and median statistics.

In this context, the weights of the decision criteria have been determined using the analytic hierarchy process (AHP) method. Alternatives have been ranked according to the compromised solution using the Vlse Kriterijumska Optimizacija Kompromisno Resenje (VIKOR) method. The AHP method has been preferred due to its ability to accommodate a large number of independent criteria, reveal dominance relationships among independent criteria, its suitability for group decisions, and its ease of practical application [13]. The VIKOR method offers advantages such as a consensus-based structure that reduces conflicts among decision-makers, the ability to rank alternatives without the need for pairwise comparisons, and its foundation on proximity to the ideal solution [14,15]. VIKOR facilitates decision-making by increasing the contribution of decision-makers to the process, helping to prevent potential conflicts, and making it easier to arrive at more accurate outcomes. Additionally, the VIKOR method can provide compromised solutions when the advantage condition is not met, making it adaptable to problems requiring such solutions. Studies in the literature demonstrate that the combined use of AHP and VIKOR has yielded successful results in complex decision-making processes, similar to dam site selection [16]. For this reason, an integrated model that combines the strengths of both methods has been implemented in the study. Among the alternative methods examined, the technique for order preference by similarity to ideal solution (TOPSIS) method provides more stable results in cases where the criteria are homogeneous (either all benefits or all costs). However, in this study, the TOPSIS method has been excluded from evaluation due to the non-homogeneity of the criteria [17].

By using AHP and VIKOR together, seismic risk maps have been created for a general assessment [18]. This study has been conducted in a region characterized by a higher seismic risk, utilizing a more extensive and detailed set of criteria through an integrated methodological approach.

In this study, the spatial suitability of the existing dams in the Sakarya Basin, located in Turkey’s North Anatolian Fault Zone, has been analyzed using MCDM methods. Considering six independent criteria, including earthquake, geological and geotechnical properties, valley characteristics, expropriation status, environmental impacts, and climate and meteorological conditions, a comparative assessment has been conducted among seven different dam locations.

The novelty of the study arises from the simultaneous and holistic evaluation of seismicity, environmental sensitivity, and the likelihood of sudden, high-flow floods using MCDM methods in a fault zone such as the Mediterranean basin, where seismic hazards are intense. In the literature, there has been no integrated AHP–VIKOR study that selects dam sites using such multidimensional criteria in an area close to the North Anatolian Fault Zone. This study proposes a systematic and comprehensive approach to dam site selection in the Sakarya Basin, a high seismic risk area that has not previously been analyzed using the selected evaluation criteria, thereby providing decision-makers with a reliable, applicable, and analytically grounded method, contributing to the literature at both the methodological and practical levels.

2 Methods used

The aim of MCDM methods is to identify the most accurate solution among multiple alternatives evaluated based on numerous criteria. The impartial and accurate collection of data is crucial for ensuring the reliability of the results. Data are typically gathered through expert consultations and/or surveys. Depending on the problem at hand, these methods can be applied individually or in an integrated manner.

2.2 VIKOR method

VIKOR is a method designed to obtain a compromise solution by establishing a ranking under the defined criterion weights. This method ranks all alternatives based on their scores, identifying the best and worst solutions. For benefit criteria, the best result represents the highest value ( f i + = max f _ij ), while the worst result corresponds to the lowest value ( f i − = min f _ij ). Conversely, for cost criteria, the best result is defined by the smallest value ( f i + = min f _ij ), while the worst result is defined by the largest value ( f i − = max f _ij ). In this context, the best and worst functions are determined for each criterion.

A decision matrix is constructed with criteria in the rows and alternatives in the columns. The best and the worst values for all criterion functions are determined. The values of S _j and R _j are then calculated. Separation measure is represented by S, and regret measure is represented by R. The parameter Q symbolizes the maximum group benefit, j denotes the alternatives (j = 1, 2, 3 … m), and i denotes the criteria (i = 1, 2, 3 … n).

(6) S j = ∑ i = 1 n w i ( f i + − f i j ) ( f i + − f i − ) ,

(7) R j = max w i ( f i + − f i j ) ( f i + − f i − ) ,

(8) Q j = v ( S j − S + ) ( S − − S + ) + (1 − v ) ( R j − R + ) ( R − − R + ) .

In this context, S ⁺ represents the minimum value among S _j values, while S ⁻ denotes the maximum value. Similarly, R ⁺ indicates the minimum value among R _j values, and R ⁻ signifies the maximum value. The parameter v represents the weight of the maximum group benefit, whereas (1 − v) reflects the weight of the regrets from opposing views. In scientific studies, v is typically set to 0.5. The obtained S, R, and Q values are sorted in an ascending order, and the alternative with the minimum Q value is considered the best. Subsequently, two conditions are checked.

2.2.1 Condition 1: Acceptable advantage

(9) Q (A(2)) − Q (A(1)) ≥ D ( Q ) D ( Q ) = 1 n − 1 .

In equation (9), A(1) denotes the best alternative with the lowest Q value, A(2) represents the second-best alternative, and n refers to the number of criteria.

2.2.2 Condition 2: Acceptable stability

The alternative A(1) with the best Q value should have achieved the highest score in only a few instances of S and R values. All alternatives sorted in an ascending order (A(1), A(2), … A(M)) are considered a common solution set.

If the second condition is not met, the alternative A(1) in the first position and the alternative A(2) in the second position are recommended as optimal compromise solutions. If the first condition is not satisfied, the relationship Q(A(M)) − Q(A(1)) < D(Q) is checked. If neither condition is met, the process should be revisited, and the data should be revised. The flow chart of control conditions is presented in Figure 1.

Figure 1

Flow chart of control of conditions.

The step-by-step algorithm illustrating the integrated functioning of the AHP and VIKOR methods is presented in Figure 2.

Figure 2

Step-by-step algorithm.

3 Application area: Sakarya Basin

The Sakarya Basin is located in the northwest of the Anatolian Peninsula and is one of the 25 river basins in Turkey. The area of the Sakarya Basin is approximately 53,800 km², and its total length is 824 km. The Sakarya Basin is surrounded by the Akarçay, Susurluk, Konya, Western Black Sea, and Kızılırmak Basins. Annually, 226 million m³ of water is transferred from the Western Black Sea Basin, and 55 million m³ from the Kızılırmak Basin to the Sakarya Basin. Additionally, 64 million m³ of water is transferred from the Sakarya Basin to the Marmara Basin each year. Approximately 53% of the Sakarya Basin is allocated for agricultural land, while 44% consists of forested and semi-natural areas. About 22% of the agricultural land is irrigated, and roughly 25% is left fallow [19].

The Sakarya River is the main river of the Sakarya Basin and is the third longest river in Turkey. It originates from the Çifteler and Sakarbaşı springs south of Eskişehir, at an elevation of 847 m above the sea level and flows into the Black Sea from the west of Karasu. It is surrounded by the Haymana Plateau, Elmadağ, and İdris Mountains to the east, Uludağ and Domaniç Mountains to the west, and Bolu Mountain to the north. The appearance of the Sakarya River on the map is shown in Figure 3. The Sakarya Basin experiences a range of climates, including Black Sea, Marmara-type Mediterranean, and Central Anatolian continental climates. A significant portion of the basin is located in the North Anatolian Fault Zone, a first degree earthquake zone.

Figure 3

Map of the Sakarya River [20].

4 Results

5 Conclusions

In this study, the locations of seven dams in the Sakarya Basin were evaluated using AHP and VIKOR methods based on several criteria. This research introduces a novel approach by simultaneously assessing seismicity, environmental sensitivity, and the risk of sudden flooding through MCDM methods in the Mediterranean basin, a region prone to seismic hazards. Notably, there is a lack of integrated AHP–VIKOR studies for dam site selection based on such multidimensional criteria near the North Anatolian Fault Zone. By providing a systematic and comprehensive method for selecting dam sites in the high seismic risk Sakarya Basin, this study offers decision-makers a reliable and practical solution, enriching both methodological and practical contributions to the existing literature. The obtained results are listed as follows:

• AHP and VIKOR methods have demonstrated the ability to identify the best compromise solution and the riskiest alternative.

• While conducting risk analyses of the locations of the dams through various scenarios, it is understood that, in addition to traditional methods such as event tree analysis, Monte Carlo simulation, or SWOT (strengths, weaknesses, opportunities, and threats) analysis, MCDM methods can also be utilized. In the site selection problem, the application and ease of use offered by these methods highlight AHP and VIKOR among the MCDM techniques.

• In situations where different conditions and criteria are applicable, it is understood that the risk statuses of dams can be determined using the employed methods. In this study, the prominent criterion is the earthquake, and in the initial scenario, the weight of the earthquake is 0.328. In the sensitivity analysis, when the weight of the earthquake criterion is increased by 10%, the A2 alternative ceases to be the optimal solution. Conversely, when it is decreased by 10%, it alters the ranking of the alternatives. This situation demonstrates the impact of criterion weights on the selection process.

• According to the obtained results, the region that is most advantageous in terms of earthquakes is the area where A1 and A2 are located. Therefore, it is understood that constructing a potential new dam or structure in this zone is appropriate.

• By using the AHP and VIKOR methods together, separate sensitivity maps can be generated for areas such as earthquake risk, flood susceptibility, poor valley conditions, and high expropriation costs. This can illuminate the selection of the best and worst alternatives and facilitate the creation of risk maps.

• The proposed integrated method for determining the best location among existing dam sites allows for the addition of new criteria and alternatives due to its flexible nature. It is believed that this method can be used not only for evaluating the locations of existing dams but also for quickly, easily, and consistently determining the site selection for future dams.

In the AHP method, since the criterion weights can be determined by experts in the field and/or through surveys, the reliability of the results will increase to the extent that more expert opinions and information are included in the research.

Since the region where the study is conducted is classified as a first-degree earthquake zone, the most hazardous situation for the dams located in this region is earthquake. Therefore, the weight of the earthquake criterion is superior to the other criteria.

In future studies, the criterion weights can be re-evaluated in different regions where other criteria, such as flooding, erosion, mining activities, or expropriation issues, carry more influence, allowing for the identification of areas at risk. For example, in a region where the effects of climate change are being observed and precipitation patterns have become irregular, the weight of the climate and meteorological condition criterion will be superior to that of the other criteria. With this composite method, precautions can be taken for areas at risk, or locations for new structures can be selected. It is recommended that such approaches be included in the project planning phase of municipal urban planning processes.