JWSS - Journal of Water and Soil Science

Catchment prioritization in terms of natural disaster intensity as well as prevention and control practices plays a main role in the natural resources and watershed management. In this study, a total of 24 sub-catchments in the Zohreh-Jarrahi basin were prioritized according to their morphometric parameters and using the mixed model of TOPSIS-Multivariate regression. A total of 12 morphometric parameters including constant component of channel maintenance, drainage density, ruggedness number, infiltration index, stream power index, stream frequency, slope, drainage texture rate, relief rate, form factor, bifurcation ratio and topography wetness index, in addition to rainfall, were studied and scored. Parameters were weighted by using multivariate regression and the spatial distribution of the observed flood events. TOPSIS model was used for the prioritization process. The results obtained from the weighting analysis showed that the ruggedness number, slope and rainfall had the highest effect on flooding in the study area with the score of 0.068, 0.024, and 0.016, respectively. According to the prioritization results, sub-catchments of Seidoon, Emamzadeh Jafar, and Takht Deraz, which had the minimum distance to the positive optimum (0.0028, 0.0029, and 0.0029, respectively) and the maximum distance to the negative optimum (0.0097, 0.0098 and 0.0095, respectively), showed the highest flooding intensity with the score of 0.7745, 0.7690 and 0.7625, respectively. In order to validate the results, prioritization results were compared to the observed flood events. Validation results also indicated the efficiency of the mixed model in delineation of catchments prone to flooding. Three sub-catchments of Seidoon, Emamzadeh Jafar and Takht Deraz were observed to have the highest number of observed flood events, thereby showing the high effectiveness of the model and also, the role of the morphometric parameters in flooding.

Soil erosion has been one of the most important problems of watersheds in the world and is considered one of the main obstacles to achieving sustainable development in agriculture and natural resources. Identifying and prioritizing regions sensitive to soil erosion is essential for water and soil conservation and natural resource management in watersheds. The present research was performed in 2021 year to prioritize the soil erosion susceptibility in 12 sub-watersheds of the Roudzard watershed in Khouzestan province using morphometric analysis and multiple criteria decision-making (MCDM) methods. In this regard, 11 morphometric parameters including shape parameters such as compactness constant (Cc), circularity ratio (Rc), form factor (Rf), elongation ratio (Re), linear parameters such as drainage density (Dd), stream frequency (Fs), drainage texture (Dt), bifurcation ratio (Rb), Basin length (L), Length of overland flow (Lg), and topographic parameter including Ruggedness number (Rn) were extracted and their relative weights were calculated using Analytic Hierarchy Process (AHP). The prioritization sub-watershed to soil erosion was performed using TOPSIS, VIKOR, and SAW methods, and the results were combined using rank mean, Copeland, and Borda methods. The final prioritization was compared with the amount of specific erosion in the MPSIAC model by determining Spearman's correlation coefficient. The result of the evaluation of morphometric parameters by using the AHP model showed that drainage density (0.161), drainage texture (0.158), and stream frequency (0.146) had the greatest effect on the erodability of the sub-watersheds. In contrast, the form factor (0.049), Elongation Ratio (0.036), and shape factor (0.026) had the least effects on erodability of the study area. In this research, the Spearman correlation coefficient between the final result of prioritizing the sub-watershed and the MPSIAC model was obtained as 0.8 in p-value<0.01. The results of prioritization of the sub-watersheds in terms of their sensitivity to soil erosion showed that sub-watersheds 11, 12, and 10 with an area of 191.83 km² are categorized as very sensitive to soil erosion due to high value of linear parameters, low value of shape parameters, sensitive geology formation, and poor vegetation cover and located in rank 1 to 3, respectively. According to the results sub-watersheds 11, 12, and 10 have the highest amount of specific erosion equal to 16.03, 12.48, and 11.6 tons per hectare per year, respectively. Therefore, these sub-watersheds are a priority for watershed management operations. The results of the present study showed that MCDM methods and morphometric analysis are suitable tools for identifying areas sensitive to soil erosion and using the combined methods of the results and it is possible to take advantage of each of the different multi-criteria decision-making methods.