Flood Susceptibility Mapping using the Frequency Ratio Method in Khiav Chai Watershed, Ardabil

The severity and frequency of floods, depends on watershed characteristics, including shape, slope, drainage density and terrain parameters. Also, hydrological characteristics such as rainfall, storage, interception, infiltration, and anthropogenic activities can intensify or reduce the flood losses. Determining flood-prone and flood-prone areas is a prerequisite for flood management planning and damage.

This study was conducted to assess the flood susceptibility of Khiavachai sub-watersheds located in the west of Ardabil province with an area of 12,680 hectares using frequency ratio method. Parameters of elevation, slope, land curvature, topographic wetness index, distance from rivers, direction, drainage density, hydrological soil group, geology and land use were used to assess flood sensitivity and prioritize sub-watersheds. The spatial map of selected parameters was prepared in raster format. Then, according to the historical flood events, the spatial location of 107 flood points in the area was determined. The observed flood event points were randomly divided into groups consisting of 74 points (70%) for calibration and 33 points (30%) for validation. Then, by comparative analysis between the occurrence of previous floods and environmental parameters affecting the occurrence of floods, the impact weight of each class of parameters was obtained. Finally, a flood probability map of the study area was obtained.

According to the flood potential map, flood susceptibility of Khiavachai watershed was shown as five classes with very high, high, medium, low and very low levels. The results showed that the sub-watersheds (1 and 2) adjacent to the outlet of the basin have the highest flood sensitivity. In other words, flooding of sub-watersheds located downstream of Khiavachai watershed is due to runoff accumulation and high flood prone due to the impact of other variables of slope and rainfed agricultural land use.

Protecting the river and carrying out various watershed management operations to convey the flow in these areas can reduce the potential damage caused by floods. The proposed flood sensitivity map can be the basis for prioritizing flood areas as well as control measures for flood management. Therefore, watershed management measures to control floods in this area are more important.