مهتاب فروتن دانش

Simulation of the rainfall-runoff process in a watershed is highly important from the point of view of hydrological issues, water resources management, river engineering, flood control structures and its storage. Rainfall-runoff estimation using a distributed hydrological model and the technique of GIS has become possible, practical and common. The Wetspa model is a distributed model simulating runoff and water balance that is performed at different time scales including hourly or daily basis. In this research, the discharge is simulated using Wetspa model in the Ghorichay watershed. This watershed (as one of the sub-watersheds of Gorganrood) with an area of 2481.5 ha is located in the south of Ramian city in Golestan province. The data used by the model are land use maps, soil texture, digital elevation model, precipitation, evaporation, temperature and discharge (for calibration and validation of the model). Calibration of 13 parameters was performed manually and automatically for 7 years at the beginning of the statistical period and model validation was performed for a period of 5 years. The results of the model evaluation show the accuracy of discharge simulation and very good agreement between the simulated data and observations based on the Nash-Sutcliffe criterion of 67.21% in the calibration period and 76.34% in the validation period. Also, the discharge calculated by the Wetspa model for the whole watershed was 28.31%, which in comparison with the observed discharge of 30.12% indicates a good simulation of the model.

1- Landuse change due to human activities is one of the important issues in regional planning. Considering the advantages and capabilities of the distributed hydrological models, they are appropriate for the survey of landuse changes as well as their quantitative estimates. Land evaluation methods are used to determine the compatibility of the land according to land capability, identification of effective factors on the floodwaters potential of the basins and zoning of the basins which are essential for runoff capability. The land is used according to their potential. For this purpose, the remote sensing data and geographic information system (GIS) were used to identify the factors affecting the flood potential and zoning of the basin in terms of flood potential.
2- THEORETICAL FRAMEWORK: In this research, a hydrological distribution model of WetSpa is used to simulate the hydrological components. This study examines the Simulation of optimal scenarios of urbanization impacts on flow hydrograph and sediment concentration using WetSpa model in Ziarat watershed in Iran. In this study, TOPSIS method and GIS were used to model the suitability of land for urbanization, providing optimal scenarios.
3- In this study, the basic WetSpa model inputs were the maps of a digital elevation model (DEM), land use and soil type in GIS raster format, and hydrometeorological data including hourly precipitation, evapotranspiration, temperature and sediment. In ArcGIS software, the distributed required maps for the model were extracted using the model input maps. Then, the model was implemented using these maps and data on rainfall, evapotranspiration, temperature, flow rate, sediment. With the help of the reference tables in the ArcView software environment, the spatial parameters of the model were determined in each cellular network.
After modeling the suitability of land for residential development through TOPSIS and GIS methods, the effects of the optimal scenario of residential development on the hydrograph and sediment were assessed. According to expert opinions, three scenarios including the current state of the residential areas of the basin, the development of residential areas with alternative low forest cover, and the residential development with alternative crops were considered, and also WetSpa model was implemented through mapping the three scenarios.
4- The accuracy of flow simulations based on the Nash-Sutcliffe model efficiency was 0.67.The evaluation of suspended sediment simulations for the calibration period based on the Nash–Sutcliffe criteria was 0.63 for the suspended sediment concentration. According to the assessment criteria considered in this study and using TOPSIS, 37 hectares of Ziarat watershed area conditions are to create residential area. After running WetSpa model with the optimal scenarios, increased roughness coefficient reduced the flow velocity and runoff coefficient as well as the peak discharge watershed. Also, the amount of suspended sediment concentration and sediment transport was reduced to the current land use scenario. Thus, by applying the optimal scenarios, urbanization, flow hydrograph and sediment density showed better conditions in comparison to the current land use scenario.
5- CONCLUSIONS & SUGGESTIONS: Changes in the flow hydrograph parameters are insignificant among the scenarios. After applying optimal scenarios, the extent of residential areas has decreased, which has led to a slight decrease in surface runoff and peak discharge in Ziarat watershed. By applying the optimal scenario, the amount of runoff coefficient has decreased slightly, which is a slight decrease in runoff coefficient due to a slight increase in penetration and evaporation. Also, the coefficient of roughness has increased slightly with the application of optimal scenarios, which is due to the reduction of the size of residential areas in the optimal scenarios. After applying the optimal scenarios, the flow velocity has been reduced slightly, which is a slight decrease in flow velocity due to a small decrease in the runoff coefficient and a slight increase in roughness coefficient. So, with the implementation of the optimal scenarios for the development of residential areas, hydrograph and sediment had better conditions than the scenario of the current state of residential areas. According to the results of this study and similar studies in Ziarat watershed, it is hoped that the authorities pay more attention to the crisis in the watershed and the increase in the indiscriminate and unprincipled residential areas in the watershed so as to prevent the unexpected consequences of the change before it can be prevented.

Certain kinds of land use can change the hydrology of the Watershed, altering the way water and pollutants move through the drainage basin. For example, as an area of land is converted from open space (e.g., woodland) to residential, the amount of runoff for that area of land will increase as the amount of impervious surface increases. Rain, which would have once seeped into the soils beneath the forest floor and been absorbed by tree roots, instead flows off impervious surfaces (roofs, driveways, streets, parking lots, etc.) into the nearest stream, pond, or lowland area. Landuse change due to human activities is one of important issues in the regional planning. In many areas of Iran,land use and land management, regardless of land ability. This caused the loss of capital and reduce the capacity of the environment.Land suitability is the fitness of a given type of land for a defined use. The land may be considered in its present condition or after improvements. The process of land suitability classification is the appraisal and grouping of specific areas of land in terms of their suitability for defined uses. Land evaluation is a process for matching the characteristics of land resourcesfor certain uses using a scientifically standardized technique. The results can beused as a guide by land users and planners to identify alternative land uses.
In this study, using multi-criteria decision making and GIS to modeling suitability of land for urban development, and determining the compatibility between existing applications, in Ziarat watershed of Golestan province, was investigated. Ziarat watershed is important in Golestan Province and yet critical in terms of land use change, Erosion and flooding. In This basin in recent years, regardless of ecological capability for urban development and the lack of attention happened land use change. In this study, referring to the 10 experts in the relevant fields and using Analytical Hierarchy Process (AHP) is a weight for each criterion.The analytic hierarchy process (AHP) is a structured technique for organizing and analyzing complex decisions, based on mathematics and psychology.In this study combining maps of criterion and suitability of land for urban development of SAW and TOPSIS technique was used. Finally, the study examines the compatibility between existing land use in the Ziaret watershed of Golestan province has been paid.
According to the results, the residential areas using TOPSIS and SAW techniques were 37 and 79.4 hectares of the total area of the Ziarat watershed, respectively. But the current situation residential areas in the watershed were 141.3 ha. In modeling suitability land for urban development due to the presence of spatial dependence between criterion maps, the best way to combine criteria and calculate the suitability of the user, using the TOPSIS technique. The results land uses compatibility showed that, residential land use with compatibility 0.118245 was lowest compatibility between current land uses in the watershed.
In conclusion, given the ability of GIS and multi-criteria decision-making methods in modeling the suitability of land for urban development, the magnitude of the expert opinions are more accurate and more up to date data, the use of these techniques and tools associated with a better outcome.As a result this technique is very effective in the watershed the case lack of data. Also when there exist complications due to a number of qualitative and quantitative criteria, MCDM play an important role.As the results of land suitability modeling using SAW and TOPSIS techniques with the use of specific software functionality ArcGIS 10.1 is clear that a small area of the basin have been created conditions of urban areas. These areas are mainly in places where the experts and according to the evaluation criteria studied in this research are a perfect opportunity for urban development, has been created.According to results of Land suitability modeling in the catchment area of residential areas is more than twice the land area.Also residential areas have been constructed in the basin in inappropriate places such as steep slopes and river boundaries, and have not conditions residential.