Within multicriteria problems we can distinguish two different groups. On the one hand, those decision problems in which the set of alternatives to be considered by the decision-making center is infinite, both in the monochiteria and in the multicriteria case, they are usually called continuous problems given the mathematically continuous nature of the set of feasible solutions.
On the other hand, there are discrete decision problems in which the set of alternatives to be considered by the decision-making center is finite and usually not very high. The practical interest of discrete multicriteria problems is evident. Thus, there are many decision contexts in which a reduced number of possible alternatives or choices must be evaluated based on various attributes.
For the appropriate treatment and analysis of the type of problems mentioned last, a large number of Multicriteria Decision methods have been developed, all of them of great interest and important application in practice. Specifically, we will refer to a wide set of multicriteria decision methods that can be grouped together under the common name of Overcoming Methods, since all of them revolve around the theoretical concept of overcoming relationships, proposed by a group of French researchers in the mid-years. sixty and that today has a wide acceptance within the world of the Discrete Multicriteria Decision. They are:
- The Analytical Hierarchies Method (AHP). The ELECTRE Method. The axiomatic Method of ARROW and RAYNAUD.
All these discrete methods are characterized because they are overclassification methods. What does this mean? Alternative A over-classifies alternative B (or alternative A is preferable to alternative B), when A is equal to or greater than B in a majority of criteria and when in the other criteria the difference in score is not too important.
Basic foundations of overclassification methods:
- They are theoretically less robust but easier to apply to real problems. They have a reduced number of alternatives or possible choices that must be evaluated based on various attributes or criteria.
We cannot fail to mention that over-classification is established based on two concepts: concordance and discordance. The concordance quantifies how much for a large number of attributes alternative A is more preferred than B. The discordance quantifies the extent to which there is no attribute for which B is better than A.
In our practical case, we will develop the Analytical Hierarchies (AHP) method , which is based on obtaining preferences or weights of importance for the criteria and alternatives. For this, the decision maker establishes "value judgments" through the Saaty numerical scale (from 1 to 9) comparing both criteria and alternatives in pairs.
For the application of this method, it is necessary that both the criteria and the alternatives can be structured hierarchically. The first level of hierarchy corresponds to the general purpose of the problem, the second to criteria and the third to alternatives.
| Value | Definition | Commentary |
| one | Equal importance | A and B are equally important |
| 3 | Moderate importance | A is slightly more important than B |
| 5 | Large importance | A is more important than B |
| 7 | Very great importance | A is much more important than B |
| 9 | Extreme importance | A is extremely more important than B |
CASE STUDY:
The availability of water resources in quality and quantity can determine the potential for economic growth of a country, due to the variety of consumption and production activities that depend on it. The Sarapiquí river basin is one of the most important for Costa Rica in terms of the use of its water resources, widely used for the generation of electrical energy, consumption, fishing, shipping and ecotourism activities. However, the basin has problems of deterioration of natural resources, such as deforestation and forest fragmentation, change of land use and inadequate use of water.
For this reason, the generation of information and tools that allow directing the scarce financial resources to promote a process of planning the development of the basin is considered a priority. To satisfy this need, the present investigation was carried out with the objective of developing an Analysis methodology, for the identification of priority areas of water resource management in the Sarapiquí river basin, Costa Rica.
Methodology
- Description of the study area:
The basin is located in the northern sub-slope of the country (Caribbean slope) between 10 ° 05 'and 10 ° 50' of North Latitude and 83 ° 52 'and 84 ° 20' of West Longitude. It comprises areas of the provinces of Heredia, Alajuela, San José and Limón, it has an extension of 2025 km (INEC 2000) and three perfectly differentiable levels (high, medium and low basin) from its source to the mouth of the San Juan river, border with Nicaragua.
In the basin, 51 communities and 71 peasant settlements are registered, mainly in the middle basin (IDA 2002). The population is 51,454 inhabitants and 59.4% of the workers are engaged in agricultural and livestock work. The literacy of the population over ten years of age is 91.1%. The hydrological network (703.6 km) is made up of a main current called the Sarapiquí River, 18 tributaries and some 16 streams.
Nine life zones are recognized in the basin; the climate is tropical rainy, with an annual precipitation between 3000 and 5000 mm. The elevation range of the basin ranges from 2,700 to 10 meters above sea level, with various types of relief: plains, foothills, low plains, slopes from rolling to rugged, valleys and hills and a mountainous relief with ridges and peaks. The predominant coverage is forest (54.7% of the area), 51.4% of this coverage is within protected wild areas in the upper part of the basin; the rest are fragmented forests with different levels of intervention (ITCR 2000). According to FONAFIFO (2002), since 1997 payments for environmental services have been assigned in 30,346 ha distributed throughout almost the entire basin.
- Characterization of the basin and identification of the main users of the water resource:
The biophysical and anthropogenic aspects of the basin were characterized in detail through the generation of primary information and review of secondary information.
The information was digitized using the GIS tools. Most of the data required descriptive statistical analysis for transformation and adaptation to the area of interest. The identification and characterization of the main users, as well as the qualitative estimation of the perceived benefit, were made in space (location and areas of influence of use) and over time (identification and characterization of current and potential users). used a semi-structured qualitative interview, subdivided into two thematic sections: description of the productive activity and form of water use by types of users. The main users were grouped by uses: human consumption, agriculture (livestock, agriculture and agribusiness), river transport,tourist activity (hotels and recreational navigation) and hydro-energy production.
Priority of areas for water resource management through Multi-Criteria Analysis (AMC)
A preliminary list of priority criteria was proposed, discussed, and validated in a workshop with experts and stakeholders in water resource management (local leaders, representatives of government institutions and NGOs, private companies, natural resource managers, and researchers). With the workshop, a final list of criteria was obtained, the conceptual definition of each one and the priority focus of water management areas: quality and usable quantity in the basin.
The criteria were evaluated by means of an opinion survey of the same experts (electronic consultation), using as input the detailed information of each criterion and the evaluation mechanism within and between criteria. Each criterion was rated on a scale of 1 to 5 (higher values indicate a higher degree of management priority). The assessment between criteria consisted of weighing them on a percentage scale, according to their degree of influence (Table 1).
Table 1.
Priority criteria of areas for water resource management in the Sarapiquí river basin, Costa Rica.
Percentage value of water management priority
Criteria Quality Quantity
| Precipitation | 10 | 35 |
| Proximity to the river | twenty | |
| Well depth | fifteen | |
| Current land use | 10 | |
| Population density | 5 | |
| Proximity of the road to the river | twenty | |
| Dry months | 5 | 35 |
| Soil texture | 5 | 10 |
| Pending | 10 | twenty |
The results of the expert assessment were standardized to be subjected to multicriteria analysis by means of the spatial analyst (Spatial Analyst) with the tools of the ArcView 3.2a Model Builder (MB). The initial information layers correspond to the databases of each criterion, transformed into raster format. Two independent spatial analysis projects were created: one for the priority of water quality management areas and another for the usable quantity.
The modeling procedure began with the entry of the information, later the categories of values were created by criteria and finally the attributes that describe the priority criteria were introduced. The general table of priority criteria was constructed with the results of the assessment within and between criteria (see an excerpt from the table in Table 2). The analysis concluded with the execution of the model, which related the spatial information and the coding of the general table of priority criteria with their respective evaluations. The result of the AMC was the generation of maps and databases to determine the priority areas for managing the quality of the water resource and the usable quantity of the water resource.
Table 2.
Extract from the general table for the assessment of priority criteria for the management of the quality of water resources in the Sarapiquí River basin, Costa Rica.
Information layers (%) Categories Attributes Values
| Proximity of the river: | twenty | one | 0 - 50 | 5 |
| The distance of communities | two | 50 - 100 | 5 | |
| and productive activities to | 3 | 100 - 300 | 4 | |
| rivers is an indicator of | 4 | 300 - 500 | 3 | |
| risk of contamination | 5 | 500 - 9 757 | two | |
| by anthropogenic sources | No data | No data | Restricted |
Additionally, an AMC model was generated in a scenario that considers the reforestation of 200 m on both sides of the river banks of the basin as a measure of water resource management. In a raster format, the buffer zone of the reforested areas was created, which was superimposed on the current land use information layer used in the preparation of the model of priority areas for water quality management. The new current land use information layer replaced the one used to determine the water resource quality model, but the remaining eight criteria were retained with their respective assessments (considering that reforestation will have a coverage effect similar to that of secondary forest) and the general table.The model was deployed and a new quality map of the water resource was obtained under the scenario of recovery of the vegetation cover on the banks of the rivers of the basin.
Results and Discussion
- Condition of the water resource:
The state of the water resource in the basin and the interrelation of the resource with the activities of the users show marked differences throughout the basin. Each user group has specific needs in terms of water resources and their use causes changes in water conditions; This situation is more evident as one descends into the basin. The Sarapiquí River is considered non-potable in terms of biological quality (total coliforms, faeces and potability), due to the high degree of bacterial contamination. The users of the water resource agree that the river has undergone changes in a short time, mainly due to sedimentation in the channels, the decrease in water in wells, streams and springs, and deforestation of the banks.The current and potential causes of degradation are due to the existence of particular biophysical and anthropogenic characteristics that affect both the quality and the quantity of usable water.
Water quality: A particular condition of the anthropogenic development of the basin is the high degree of dependence of some activities on the main channels. The degree of access of residents and tourists to the river banks is high in some sectors, because the waters are used for multiple purposes. This is evident in the location of road and urban infrastructure starting in the middle basin, from where the main road runs parallel to the river bed, a few meters from urban areas, tourist sites and production systems. In the basin there are no natural causes of deterioration in water quality; the causes are due to anthropogenic agents: dumping of domestic garbage, sewage, pollutants from agricultural activities, agro-industrial waste and river transport.
Usable amount of water: The abundance of water in the basin has been erredicated by natural causes (dry months and surface runoff), as well as by human action (loss of forest cover, contamination, sedimentation and the presence of reservoirs for hydroelectric production). Likewise, in the basin there is no way to manage and regulate the use of the channel for navigation and tourism, which has caused controversy among users.
Analysis of priority models for water resource management areas
The results of the area priority model for water quality management show that the Very High priority category is non-existent and the High priority reaches just 0.4%, which represents 810 ha of the total area of the basin. The predominant areas were Medium and Low priority (the latter for 79.0% of the area). The predominance of forest cover in the basin determined low risk values for water quality conditions, according to the priority criterion of current land use. However, it should be taken into account that the base coverage information was generated in 1992 and that the field visits corroborated the outdated information; Additionally, the level of detail does not reflect the condition of discontinuity or fragmentation of the remaining forest in the basin.
On the other hand, highways, communities and the productive systems developed on the banks represent sources of contamination of the water resource, for which a high weight (20%) was assigned to the priority criteria: Proximity of roads to rivers and Proximity of population centers to rivers. This high relative value influenced the determination of the Medium priority zones, which is observed in the distribution pattern of these areas in the basin. The few High priority areas correspond more than anything to localities with shallow wells, where the risk of contamination is greater.
The priority model of areas of management of the usable amount of water shows a predominance of areas classified as Medium (65.3%) and Low (33.0%) priority. The model does not identify Very High or Very Low management priority sites, and the High priority category is 1.7%, corresponding to around 3,500 ha.
The Medium priority areas are located in the upper and lower basin, because rainfall in these areas is less. The limited availability of information to select priority criteria in this model resulted in the excessive influence of the Precipitation criterion (process of recharging the basin, weighted with 35%); This is a strong limitation of the model, which should desirably incorporate criteria related to water supply and demand and the measurement of flows. The middle basin has the highest demand for water and the highest level of liquid waste, elements that could not be incorporated as criteria for the model because the necessary information was not available.The upper basin presents significant High priority areas determined by the predominance of steep slopes and by the additional influence of less precipitation and more dry months.
Considerations of the priority methodology with AMC:
The AMC methodology developed with GIS tools has characteristics that make it practical for identifying priority areas for water resource management. Its application in this study demonstrated strengths related to the flexibility and versatility of its development, the opportunity to incorporate participatory elements and the possibility of manipulating secondary information to consolidate it with primary information. However, it is necessary to identify their weaknesses and needs for improvement in approaching studies of this nature.
Depending on the knowledge of the basin problem, the availability of information and its compatibility with the requirements of the AMC, this will be the effectiveness of the selected priority criteria and their assessment. It is essential to analyze the criteria according to the particular characteristics of the basin; In addition, it is convenient to work with a wide number of criteria to reduce the possible influence that one criterion has on the others.
The wide extension of the study area did not allow generating primary information on key issues to define management priorities, such as the capacity of aquifer recharge and location of main users.
In addition, the scale and level of detail of some secondary information (current land use, soil texture, and population density) required prudent treatment in digital databases, so the information had to be modified and adapted at times. to perform spatial analysis.
The results of the research suggest that the approach to the management of areas to ensure water quality in the basin should be specifically oriented to the education of the sources of contamination by correcting productive practices and environmental education to the communities surrounding the courses of water, as well as the recovery of the natural cover on the banks of the drains of the middle and lower basin. For this reason, the model was developed under the scenario of reforestation of the river banks for the priority areas of future water quality management, which showed an evident recovery of the conditions of the basin as a pattern. In this model, the Very High Priority category is non-existent, and the critical areas of Alta, M ediana and Low Priority were 0.1%; 18.9% and 8.1, 1%,respectively, of the total area of the basin.
Conclusions and recommendations
In the AMC it is recommended to have as many priority criteria as possible to reduce the influence of any particular criterion. In addition, it is convenient to make the evaluation of criteria based on the characteristics of the basin and the direct influence that the basin has on the conceptualization of each of the criteria, to avoid any criteria being overvalued.
The MB tool is practical, flexible and feasible for applying AMC and for identifying priority areas. It can be used as a modeling tool for decision-making in watershed management and recovery strategies, as well as a monitoring tool to evaluate the performance and results of its implementation. Also, it can be used with a limited base of secondary information, supplemented and updated as new information is generated.
It is recommended to apply and validate the methodology in a smaller basin, where more accurate primary information and more efficient field verification can be generated.
Identifying priority areas in hierarchical categories provides information on where short, medium and long-term efforts should be directed towards the recovery of water resources. The application of mitigation measures, such as the riverbank reforestation plan, can have considerable effects on the recovery of priority levels of water quality.
It is necessary to address the problems and possible solutions regarding the management of the water resource with a comprehensive approach that recognizes the multisectoral nature of its use. It is desirable to have decentralized authorities that coordinate and promote efforts for water management, such as compensation programs for environmental benefits and the internalization of environmental costs for the management of the water environmental service. Such programs can be developed with the collaboration of users and providers of the water service, such as hydroelectric companies, tourism companies, agro-industries and production systems that are possible generators of funds for the management of water resources in the basin.
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