A GIS-based Decision Support System to Identify Potential Sites for Soil and Water Conservation Measures (Case Study: Kakhk Watershed)

Document Type : مقاله پژوهشی


Ferdowsi University of Mashhad


1 Introduction
Water crises and soil erosion are some of the most important challenges threating food security around the world, and Iran is no exception in this case. Watershed management measures are common practices for soil and water conservation. Identifying and prioritizing suitable sites for implementing soil and water conservation measures in a watershed is, in fact, an important decision in watershed management. To this end, the analysis of spatial data and comparison with technical standards of conservation practices is primarily required. Multi Criteria Decision Making (MCDM) analysis methods are a commonly used method of analysis combining data from various criteria. The Analytical Hierarchy Process (AHP) is a MCDM tool widely applied in order to identify the potential sites for flood water spreading, artificial discharge and rainwater harvesting. Terrace and channel terrace are historical measures in soil and water conservation in Iran. Both of these measures are commonly used for upland area to reduce steepness of hill slope. The present research aims to present a GIS-based decision support system for the site selection of terrace and channel terrace in Kakhk Watershed located in the Eastern part of Iran. Finally, the results derived from AHP are compared with the current terrace and channel terrace implemented in the watershed.
2 Materials and Methods
The case study of this research is Kakhk Watershed. Kakhk is located between 58° 31′ 22′′–58° 38′ 01′′ E and 34° 02′ 25′′–34° 06′ 14′′ N  in Khorasan Razavi Province in the Southwest of Gonabad. The above mentioned watershed drains an area of 37.8 km2. The major land uses of this watershed include Rangelands and agricultural lands. The mean of annual rainfall in this region is about 279 mm; 58.4% of this rainfall takes place during the winter.
The main criteria for allocating terrace and channel terrace were achieved through the review of past literature in the field. Based on previous studies undertaken in this field, slope, rainfall, runoff, soil depth, soil texture, distance to drainage network and economic issues were the main factors affecting the site selection of terrace and channel terrace. Therefore, spatial data were acquired and processed through Arc GIS 9.2. Software. Rainfall-elevation equation was derived through analyzing eight climatic stations near the watershed used for preparing the annual rainfall map. In order to estimate the direct runoff, the Soil Conservation Service (SCS) Curve Number (CN) method was applied. The weight of each map and classes were derived using AHP and entered in each map and classes. The AHP is a widely used multi-criteria decision-making tool which assists decision makers in planning, selecting the best alternative, and resource allocations. The selected criteria were prioritized based on the decision-making process which, in fact, judges the dominance of one criterion over another. Consistency ratio (CR) was used to assess the consistency in the comparative importance judgment. Final weights derived for each criterion were assigned and calculated in Arc GIS. Then, rasterized maps were used for producing suitability maps. Suitability levels for each map were categorized based on the obtained results from both the field survey and literature review. In order to test the applicability of the approach developed in the study, the locations with existing soil and water conservation measures were compared with locations obtained through AHP.
3 Results and Discussion
The results of the AHP analysis reveal that slope and runoff criteria have the highest weight, while the distance to drainage network has the least weight in the allocation of terrace and channel terrace. The results also indicate that 4% and 7% of the watershed are highly suitable highly for terracing. Twenty nine percent and 47% of the watershed area in the West and Southwest have low suitability and are not suitable for terracing, respectively. In addition, the results for channel terrace show that 5% and 14% are suitable and highly suitable for channel terrace. Thirty one percent and 25% of the watershed area with high slope and low depth soil have low suitability and are not suitable for channel terrace, respectively. Highly suitable sites were mainly located near the main outlet due to the existence of deep soils with suitable texture. Upland areas of the studied watershed were mainly located at the unsuitable level although the amount of rainfall was considered to be proper for conservation measures due to the limitations in slope and soil properties.
A comparison between the obtained results and the implemented measures in the watershed reveals that 59% of the area with channel terrace and 21.8% of the area with terraces are located at highly suitable levels. The mismatch between the obtained results using implemented measures may be due to not taking into account the other criteria such as social and economic issues and also people participation during the process of implementation.
4 Conclusion
The current study aims to apply a combined GIS and MCDM approach to allocate and prioritize sites for the implementation of terrace and channel terrace within the Kakhk Watershed in west of Iran. The obtained results in the present study suggest that decision support system may assist local watershed managers in soil and water conservation. Using further criteria in site selection and using more MCDM methods are also recommended for future studies.


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