Reducing the Flood Hazard Zone in the Kashan Plain Watershed through the Implementation of the Risk Land use Planning Scenario

The plains of flood rivers are among the critical points of the flood. The Kashan Plain Watershed is one of the cases that has been flooded in numerous years. There has been many economic and financial losses in the residents of this watershed. Achieving and resolving environmental management problems in the watershed scale requires an integrated approach in evaluation and management, in which the processes and all the biophysical and socio-economic effects are considered (1). In the last decade, in a comprehensive action with a subtle and flexible combination of empirical models of evaluation of capabilities, the environmental and legal support of some pioneering countries with the approval of the law required the interference of natural disasters in the context of each development program. The new horizon of the Risk land use planning paradigm was opened, and logistic link to the efficiency of the programs and realization of the multilateral goals of sustainable development, and management of its environmental hazards was accelerated drastically (2).
In recent years, several researches in the field of Flood Risk Zoning (3,4), Impact of Land Use Change on Flood Risk Area (5,6,7,8) and Effect of Intensive Use Scenario on Flood Risk Area are presented. In this study, the risk zone of flood in watershed was determined, and the new risk land use planning approach were presented based on the uses of 1985 and 2017 as a management scenario for improving the watershed.

Kashan Plain Watershed has an area equal to 5574 square kilometers. It is located south of Qom Plain, and Salt Lake, and south west of the mountains of Vulture, and east of sand dunes of The High-Rise rig of Kashan. The climate of the study area is classified according to the Domarten method in the lowland areas except the arid or desert climate, and in the highland areas except the semi-arid climate.

There are various factors that can be effective on floods based on available data from the region; 11 effective slope percentage, elevation classes, lithological units, fault distance, distance from waterways, soil type, Stream Power Index (SPI), Topographic Wetness Index (TWI), Ground Curvature, Land Use, and Rainfall, which were selected for 1985 and 2017. Afterward, their raster maps were prepared with 30 * 30 cell dimensions.

The obtained weights were applied to the relevant layers. Then, using the mapping functions, the final map of flood hazard zonation was obtained.

A set of technical validation points (64 points, 30% of the total points) were used to validate the flood risk forecast map. The flood points were overlapped with the final map using a GIS software.

In preparation of the Risk Land Use Planning, the standardization was conducted based on two fuzzy logic (0TH1) for Criteria and Boolean (0 or 1) for limitations. In the next step, the criteria and limitations were weighted according to their importance and their impact on selecting appropriate location using Analytical Hierarchy Process (AHP) method. Further, the procedure was performed by evaluation of power for 8 uses of forestry, rangeland, agriculture, aquaculture, extensive tourism, centralized tourism conservation, and rural development by combining information layers (criteria) with Weighted Linear Combination (WLC) (8).

Finally, to prepare the flood potential map in the study area, eleven maps resulted from the GIS environment were used. The final map was classified in four different areas of potential, including low, medium, high, and very high potential zones. The results showed that from 1985 to 2017, the area of low and middle class decreased by 5.8% and 4.07%, respectively, and increased by 2.22% and 2.543% respectively. The study of Goodarzi and Fatehifar (1398) corresponds to the Azarshahr Tea watershed.

Based on the 1985 and 2017 flood hazard maps, the high and very high floodplains cover most of the catchment area. This indicates the need to prioritize conservation use in the risk management scenario.

In this study, the probability map of flood risk was prepared for both 1985 and 2017 land use. Then, in order to manage the flood risk, the new approach of risk land use planning was introduced. The results show that despite decreasing rainfall from 1985 to 2017, the floods during this period especially increase around Kashan, Aran, Bidgol, and surrounding villages. This concludes that climate change adaptation-based disaster management; containment of illegal land use change in risk land use planning of Kashan Plain Watershed for sustainable development. According to the results, more dire conditions will prevail in the region in the future. Therefore, it is recommended that organizations consider strategic flood prevention plans and prioritize risk planning.