Study of Hydrogeomorphic Indices in Flood Sensitivity (Case study: Aland Chai Basin, Northwest of Iran)

Flood is a disaster that causes a lot of economic damages to farmlands, forests, gas and power transmission lines, roads, engineering structures and buildings. This study has attempted to analyze the role of hydrogeomorphic indices in flood sensitivity of Aland Chai Basin in the northwest of Iran. To achieve this aim, the study area was first divided into 15 sub-basins based on topographic and drainage characteristics using a digital elevation model (DEM) with 12.5m spatial resolution. Then, Hydrogeomorphic parameters of sub-basins have been studied from three aspects of drainage network characteristics (Such as Stream order, Streams number, Streams length, Stream frequency, Bifurcation ratio, Length of overland flow, Drainage density, Drainage texture, Texture ratio, Infiltration Number, Constant of channel maintenance, and Rho Coefficient), shape characteristics (Including Basin area, Compactness coefficient, Circulatory ratio, Elongation ratio, Form factor, and Shape Factor) and relief Properties (Relief, Relief ratio, Ruggedness number, and Gradient). Hydrogeomorphic analysis plays an important role in the analysis of hydrological behavior of the basins, especially in basins that lack information.

Aland Chai basin is located between 38, 30´ and 38, 48´ latitude and between 44, 15´ and 45, 01 longitude in the north of the West Azerbaijan province, Iran. This basin has an area of 1147.30 km2 and it is situated in the north-western part of Iran. Basin elevation variations are from 1093m in the Aland Chai River bed to 3638m above sea level in the Avrin Mountain. The main river of this basin is Aland Chai, which is one of the most important rivers of Khoy city. This basin is one of the sub basins of the Aras River basin, which surface water flows into the Aras River after joining the Qotour River. MACBETH Multi-Criteria Decision Analysis Model was used to weight the parameters and the weighting of the parameters was performed in M- MACBETH software. Bana e Costa, Vansnick, and De Corte firstly proposed MACBETH method in 1990s. The MACBETH method (Measuring Attractiveness through a Categorical Based Evaluation Technique) is based on the additive value model and aims to support interactive learning about the evaluation problem and the elaboration of recommendations to prioritize and select options in individual or group decision making processes. It helps to rank the alternatives based on aggregated value of relative weighted attractiveness of alternatives under the decision criteria. MACBETH method uses 7‐semantic scale (No, very weak, weak, moderate, strong, very strong, and extreme), which is an ordinal scale.

In the first step, the information of each sub-basin was obtained based on 22 hydrogeomorphic parameters from three aspects of drainage network characteristics, shape characteristics and relief Properties in ArcGIS software. These parameters were prepared using the geomorphological laws of Horton, Schumm, and Strahler. In the next step, all necessary weights were calculated for factors and Sub-basins using MACBETH method. The weighting results showed that among the characteristics of the drainage network four parameters of drainage texture, texture ratio, drainage density and bifurcation ratio with coefficients of 16.96, 13.84, 13.49 and 12.46 percent and three parameters, area, compactness coefficient, and Circulatory ratio with coefficients of 29.63, 27.78 and 20.37 percent among the shape parameters respectively, and two parameters of relief and slope with coefficients of 43.75 and 31.25 percent among the relief Properties were the most important parameters. On the other hand, parameters of Rho Coefficient, Shape Factor, Constant of channel maintenance, and Infiltration Number with coefficients of 0.35, 1.85, 2.42, and 3.11 had the least weight.

Floods usually start abruptly and cause irreparable damage in a short period of time. In this study, an attempt was investigated to analyze the role of hydrogeomorphic indices in flood sensitivity of Aland Chai Basin. Based on the effective parameters, flood occurrence inside of Aland Chai basin could be separated into 5 distinguished classes, from very high to very low flood susceptibility. Sub-basins ranking in terms of flood risk sensitivity based on final weights obtained from MACBETH method showed that sub-basins 1, 2, and 3 have the highest ranking and have very high sensitivity to flooding. These sub-basins comprise 286.67 km2 (24.98%) of basin area. Sub-basins 4, 9, 11, and 15 are also highly susceptible to flooding. Also sub-basins 6 and 13 have very low susceptibility toward flood occurrence. In total, about 45% of the study area has high flood sensitivity. Therefore, according to the results of the study, it is necessary to take protective measures such as watershed planning and dam construction in the sub-basins that are highly sensitive to prevent flooding or reduce potential damages in case of flooding.