نشریه پژوهش های آبخیزداری
پیاپی 140 (پاییز 1402)

In recent years, due to the rapid growth of the population, the increasing development of urbanization and the industrialization of societies, as a result, the hydrology of urban watersheds has been accompanied by many changes. These changes over time have caused floods and inundation of roads in urban areas, and on the other hand, flooding in these areas due to the density of population and facilities can cause severe damages and reduce the quality of runoff. New approaches have been proposed to manage runoff and prevent flooding and water pollution, and in this case, the development of low-impact LID is one of these approaches. The purpose of using this technique is to simulate the hydrological conditions of the urban area before development. For this purpose, in this research, the evaluation of quality parameters (BOD, TP, TN) was investigated using the best low-impact development management practices (LID/BMPs) in Gorgan city.

In the first stage, information related to intensity-duration-rainfall curves, urban and land use maps, and urban development maps were collected for Gorgan urban watershed. EPA-SWMM model was used to create a hydrological model in Gorgan city and investigate the effect of LID on runoff. According to the urban development of the region, six options of green roof, biological system, garden waterway, rain, infiltration trench and permeable covers, with a 6-hour rainstorm were considered with a return period of 2, 5 and 10 years for qualitative analysis using parameters Nitrate, phosphate and BOD.

The results of the calibration and validation of the model based on the Nash-Sutcliffe criterion more than 0.5 showed that the SWMM model has the required accuracy for simulating the quality of urban runoff. The results showed that, respectively, the green roof system, rain barrel and permeable covers have the best performance in improving the quality of surface runoff in the region by reducing surface runoff pollutants compared to the existing situation. The use of low-impact development methods in the region depends on various factors, including environmental, economic and efficiency factors. The results indicate that all the LID scenarios selected in the research were effective in improving the quality of surface runoff, but each of the scenarios showed different capabilities.

Conclusion and Suggestions:  
Even though all the LID scenarios examined in this research were effective in controlling surface runoff and improving its quality, but with the implementation of the green roof, rain barrel and permeable covers, the amounts of phosphate, nitrate and BOD compared to the existing situation and other scenarios has decreased further. As a result, the impact of green roof management measures, rain barrel and permeable cover has been greater. Finally, it is suggested that in order to improve the quantity and quality of surface runoff, these methods should be considered in the implementation priorities.

Today, the destruction of natural resources is one of the most important and serious challenges facing development programs. Soil erosion is among the processes that directly and indirectly threaten our country's soil and water resources. Water erosion appears on the earth in different forms, one of the advanced forms of which is the gulies. Gully erosion is one of the important processes of soil destruction, which in different climates causes significant soil losses and the production of large amounts of sediment. The purpose of the present research is to investigate the morphological characteristics of the gullies of Khuzestan province and the role of its influencing factors in the expansion of the gully areas.

 First, by collecting available data and comparing it to satellite image and other data, the province's gullies have been defined. The first field visit focused on verifying the integrity of these areas and correcting the gullies boundaries. The total area of Khuzestan province approximately is 64000 km2 in the dry desert climate, and more than 33,862 ha of it is under the influence of gully erosion. The hot semi-arid climate also covers approximately 12,1% of the province and 16,116 ha have experienced gullies erosion. After determining the area of gullies and dividing the areas above and below 500 ha, due to the difference in appearance, topography, and vegetation, 2 and 1 representative areas were selected from the hot-dry desert and hot-semi-arid climates, respectively, and 2 replicates were selected from each representative. Longitudinal and cross-sectional profiles of representative and replicated gullies were drawn and after soil sampling, all morphological features of the gullies were measured.

According to the results, most of the gullies of the province have been created in the plains with a low slope with deep soil and loamy sand texture, silt or silt loam with pasture, and sometimes agricultural land and U-shaped cross-section. Darkhazine and Sharif gullies, with 1260 and 912 cm, and Darkhazine gullies with 420 cm value have the maximum width of top, bottom and depth in the cross-section of 75%. Also, the gullies of Choghazanbil, Darkhazine and Choghazanbil with values of 30 cm have the lowest depth, top and bottom width in the cross-section area of 75%. The overall profile is scratched, and in terms of depth class, they are in the category of medium-deep gullies with a vertical top.

Intrinsic characteristics of soil, formation and geological type, climate, intensity of rainfall as natural factors, and destruction of vegetation, land use change and the lack of proper management, unprincipled road and bridge construction operations, construction and installation of oil facilities and electricity bars as human factors have played a role in the process of gully expansion. However, the diversity and change of the number and degree of influence of different factors from one point to another and the difference in their participation in the formation and expansion of the gully are based on the environmental conditions of the land. These conditions require that more research be carried out to identify as many factors as possible in the phenomenon of gully erosion and their participation in the formation and expansion of this phenomenon in different places and with different environmental conditions.

Lack of awareness of rural people is the main factor in the destruction, erosion, and change of natural resources. Therefore, rural development programs should be pushed towards participatory management to preserve and restore natural resources. Modification and change of behavior is done when the beliefs of the rural community change. Most people believe that preserving natural resources is one of the duties and powers of governments. But the fact is that sometimes these interventions have been destructive. Since the development of human resources is one of the basic principles in participatory management, And participatory management in rural communities is implemented at an optimal and effective level when the gap between the past generation and the rural youth can be resolved by developing education in the field of awareness regarding the correct handling of natural resources. the first step is to develop and improve the awareness and knowledge of human resources through a change in behavior, attitude, and individual skills. The infrastructural limitations of villages and their limited access to education and communication facilities make educational and promotion media one of the most important means of transferring information, knowledge, and skills to rural people.

This research, using the survey and documentation method, try to investigate the participation of residents of watersheds in West Azerbaijan province (Takab, and Shahindej) in watershed management projects and identify the most important influencing factors. The samples were selected using stratified random sampling and the data collection tool was a questionnaire. The face validity of the questionnaire was confirmed by agricultural extension and education experts and watershed experts, and its reliability was estimated to be 82% using Cronbach's alpha.

 Multivariate regression analysis with the combined method showed that income, education, and the amount of media use are the most important influencing factors in public participation. Also, there is a positive and significant relationship between the influence of the media and the active participation of the village people in watershed projects.

Therefore we conclude that, the use of educated rural youth to produce, publish or use the media can significantly contribute to increasing the participation of villagers in watershed management projects.

Marl lands are very sensitive to erosion in arid and semi-arid regions and are one of the most important sources of sediment production. Research has shown that there is a relationship between the geological characteristics of marls and different forms of erosion. In some marl formations, rangeland plant species have grown and stabilized which causes erosion control and soil stability. In order to better understand the status of these ecosystems, this study was conducted to identify the established plant species on marl lands and investigate the relationship between vegetation and physical and chemical properties of marl soil in three types of surface, rill and gully erosion in Semirom region.

Semirom is one of the marl regions that was selected for the current study in the classification and determination of marl erodibility indices of Isfahan province. In order to evaluate the erosion condition in three forms of surface, rill and gully erosion, BLM (Bureau of Land Management) form was completed in the same marl units and areas without vegetation cover. In the next step, three soil samples were collected from 0-20 cm depth in three repetitions in marl units including three forms of erosion. Physical and chemical soil properties including texture, EC, N, P, K, SAR, OC, CEC, CaSO4, pH, T.N.V and CaCO3 were measured. For vegetation studies in the study area, after preparing the floristic list of plant species, vegetation characteristics including canopy cover percentage and density per plant species, as well as the percentage of gravel and litter were measured and recorded. The statistical analysis of the data was done as a completely random design using SAS software and the averages of soil properties were compared according to the Least Significant Difference (LSD). Correlation analysis between soil and vegetation characteristics was also done by R statistical software.

Results and Discussion:
The results showed that in terms of erodibility, Marl lands with vegetation cover, had a better condition than without vegetation. The soil in the gully erosion was in better conditions in terms of nitrogen, phosphorus and organic matter and had better vegetation than the other two types of erosion. The results of correlation between physical and chemical soil properties and vegetation showed that the canopy cover factor was 95% and 86% correlated with the percentage of gypsum and the percentage of sand, respectively. The dominant species which showed the most protection capacity against erosion in surface, Rill and Gully erosions were Astragallus cephalantus, Cousinia cylindracea and Elymus gentry with 34.2, 33.3 and 22.05 percent of the highest combination of density and canopy cover, respectively. In terms of growth form, in all three types of erosion, forbs had the highest percentage of density and canopy cover.

The results of current research could be considered as a novel achievement in order to prevent soil erosion through establish appropriate species in marl lands with similar climatic conditions.

Awareness of the pattern of spatial and temporal variations of the rainfall erosivity is essential for improving soil erosion estimates, especially considering snow cover in different months. In the Caspian Sea Basin, due to the low distance between mountain regions and rainy plain, estimation of rainfall erosivity factor without considering snow cover correction coefficients is associated with a significant uncertainty. Accordingly, the current study aims to analyze the spatiotemporal variations of the rainfall erosivity factor with considering snow cover correction coefficient in the Iranian part of the Caspian Sea Basin.

To prepare monthly, seasonal and annual rainfall erosivity factor, monthly rainfall data of 56 synoptic stations of the Caspian Sea Basin were obtained from the national meteorological organization and statistical yearbooks with a common statistical period of 20-25 years (1996-2020). As a result, the rain erosive layer in different time bases using Co-Kriging geostatistical method with auxiliary variable of height above sea level with less root mean square error (RMSE) was used as the most common evaluation index and selection of the optimal method. Then the monthly snow cover layer was prepared from MOD10CM product and the rainfall erosivity for each month was modified.

Based on the results, the average annual rainfall erosivity factor of the Iranian part of the Caspian Sea Basin was 254.61 (MJ mm ha-1 hr-1), while by considering the snow cover correction coefficient, the rainfall erosivity value was redused to 210.53 (MJ mm ha-1 hr-1). Also, Bandar Anzali and Manjil synoptic stations have the highest and lowest values of the average annual rainfall erosivity factor equal to 749.30 and 162.87 (MJ mm ha-1 hr-1), respectively. In addition, after considering the snow cover correction coefficient, the highest monthly rainfall erosivity values of 27.27, 25.81 and, 25.56 MJ mm ha-1 hr-1 were observed in April, October and, November, respectively. On the other hand, 12.81% of the studied area is in the medium to very high levels of rainfall erosivity in the northern part of the Caspian Sea Basin, which can be used to prioritize different areas in order to carry out conservation measures to reduce the effect of the rainfall erosivity factor on the amount of soil erosion and sediment yield were used.

Based on the results of the current research, it can be stated that the fluctuation of rainfall erosivity in different months and seasons is also affected by the rainfall time distribution throughout the year. Therefore, the maximum amounts of rainfall erosivity in most of the studied areas correspond to the main times of agricultural activities, i.e. planting and harvesting, which are critical times for soil erosion. Investigating the spatial pattern of rainfall erosivity in the Iranian part of the Caspian Sea Basin shows many relative changes between different regions from the plains to the highlands. Although this pattern is somewhat consistent with the pattern of climate changes from drier and less rainy areas to wetter and morerainy areas, the type of precipitation and especially snow in high areas has reduced the rainfall erosivity in these areas. Therefore, the temporal evaluation of rainfall erosivity resulting from the current research, in which the snow cover correction coefficient is applied, with the timing of the presence and density of vegetation on the soil surface, provides more reliable results for land management managers and planners, especially in the agricultural sector, to choose the right type of crops for each will place the area.

Ecological quality is an inclusive measurement unit of the elements, configuration, and performance of an ecosystem in the temporal and spatial scales. In addition, assessing ecological quality could provide valuable information for experts and managers in the first step of directed planning and comprehensive watershed management. Therefore, the current research was conducted to calculate the ecological quality index (EQI) in one of the upland watersheds of Yamchi Dam, which is not without the effect of human interference.

Nir Watershed as a study area is located in the southwestern part of Ardabil Province. To carry out the current research, first, the essential variables of ecological quality assessment (normalized difference vegetation index (NDVI), fractional vegetation coverage (FVC), leaf area index (LAI), net primary production (NPP), moisture index (IM), land surface temperature (LST), soil erosion, ecological integrity index, and runoff retention index) were collected and calculated. The variables were chosen to represent the three functions of ecosystems maintaining, supporting, and regulating. After standardization, weighting of the variables was done using the advanced multi-criteria, i.e., Projection Pursuit Model (PPM). Afterward, the EQI was calculated based on the sum weight of all variables for 11 sub-watersheds of Nir.

The wide range of variability of the variables used in the entire Nir Watershed area was confirmed. In general, sub-watershed 1 had the maximum mean of the first to fourth variables (FVC, NDVI, NPP, and LAI) and the minimum mean LST. While sub-watershed 11 had the opposite situation in terms of these five variables. All five variables reflect the structure and function of vegetation and therefore the ecological quality. The status of other indicators except ecological continuity (EC) was also evaluated in sub-watershed 1 in a medium status. Based on the PPM weighting method, the FVC (0.39) has the highest importance, and moisture and runoff retention indices with an equal weight of 0.01 have been assigned the least priority. In addition, the ecological quality results showed that watersheds 11 (0.10) and 1 (0.90) respectively have the lowest and highest levels of EQI. In general, according to the zoning resultd, it was found that the northeastern and southeastern parts of the watershed have the lowest EQI which covered 29% of the area.

The results can be used as one of the main goals of managing watersheds regarding preserving the ecosystem's health and integrity. Moreover, the priority of rehabilitation budget allocation can be assigned according to the resilience degrees of studied sub-watersheds.

Given the application of hydrological response in a watershed, various methods have been used to determine this response and the results have shown a high degree of accuracy and accuracy variability depending on the data used. By reviewing and summarizing the results of research carried out in the modeling of rainfall-runoff, particularly the time-area method, it was found that in most of these studies, the concept of watershed time concentration was used, which in most of the formulas used, the physical properties of the watershed were used and the dependence of time concentration on rainfall conditions was not studied. Therefore, this study was conducted to evaluate these methods using the kinematic wave method in the GIS environment, the HEC-1 method, and optimization methods using genetic algorithms in a V-shaped experimental watershed.

Observational data available in the V-shaped experimental watershed of the University of Illinois was used for rainfall-runoff modeling. The studied watershed had an impermeable aluminum surface and two uniform side sheets with a one-sided slope towards the channel with a constant value of 1%. In addition, a central channel with a one-sided slope towards the outlet of the watershed with a constant value of 1% was present. The roughness coefficient in this watershed was determined based on trial and error at 0.014.

After preparing the time-area histogram of the watershed using each of the mentioned methods, the corresponding outflow hydrographs of the watershed were determined. Then, the results were compared with observational data, and various components of the computational hydrographs were also examined. The results showed that the performance of the genetic algorithm in determining the peak time of the hydrograph with a 15% relative error was better than the performance of the kinematic wave and HEC-1 models. Additionally, the genetic algorithm model had the highest correlation coefficient with observational hydrographs with an average Nash-Sutcliffe Index of 0.968 and an average correlation coefficient of 0.983. Furthermore, by fitting the curve to the modeling results, an equation was obtained to determine the equilibrium time of the watershed relative to rainfall intensity, with a determination coefficient of 0.999. This equation expresses the inverse relationship between equilibrium time and rainfall intensity (with a power of 0.33), i.e., doubling the rainfall intensity reduces the equilibrium time by 20%. Finally, the coefficient of the equation determining the equilibrium time for this watershed was found to be 495.2, and for each rainfall intensity, its corresponding equilibrium time can be calculated with high accuracy.

In this study, under experimental watershed conditions, rainfall-runoff modeling was performed with three categories of events and three categories of different rainfall durations, each event category having four different rainfall intensity sizes. Corresponding hydrographs were obtained for each event by examining the computational hydrographs and comparing them with observational hydrographs, and it was found that the three models had one to two percent relative error in determining the maximum runoff, but in determining the time to reach the hydrograph peak, the kinematic wave and HEC-1 models had an average error of 44%. Finally, using the correlation and Nash-Sutcliffe coefficients, it was determined that the computational hydrographs produced by the genetic algorithm method were closer to the observational hydrographs and had a higher degree of correlation. It is worth mentioning that in this experimental watershed, the dependence of equilibrium time on rainfall intensity in impermeable conditions was confirmed. It is recommended that the effect of infiltration or changes in surface roughness and the determination of the dependence size be investigated.

Soil erosion by water and wind is one of the biggest environmental threats worldwide which it has various negative consequences such as soil degradation, mitigation of soil fertility, depletion of nutrients and micro-elements, degradation of soil structure, dust storms, reservoir siltation, and etc. on the natural and anthropogenic ecosystems. Therefore, accurate information of land susceptibility to soil erosion hazard by water and wind, and production of spatial maps of these hazards are necessary for mitigation of their consequences. Therefore, the goal of this research is application of two machine learning models for the spatial modelling of water and wind erosion in the Bakhtegan basin, Fars province.

In order to generate the spatial maps of soil erosion by water and wind, we have used 20 and 16 effective factors on water and wind erosion, respectively. Before the modelling stage, the multivariate adaptive regression spline (MARS) feature selection algorithm and multicollinearity test were used to identify the most important factors controlling water and wind erosion. In next stage, two random forest and support vector learning machine techniques were applied to model soil erosion. Area under curve (AUC) was applied to assess the model performance.

According to results, land use, slope, lithology, roughness, coarse fragment, clay, vegetation cover, aspect, soil bulk density and topographic wetness index were identified as the most important factors controlling water erosion. The most important factors controlling wind erosion are including elevation, land use, wind speed, slope, vegetation cover, soil nitrogen, cation exchange capacity, lithology, aspect, clay and bulk density. The AUC value for wind erosion map generated by random forest model was 99, and for water erosion map produced by support vector machine is 96. Finally, we integrated two maps and results indicate an area of study area about 18% has very high susceptibility to wind erosion and low susceptibility to water erosion.

Due to study area has several lakes consisting of Bakhtegan, Maharlo and Tashk, and also several dams, it is so important to supply water for different purposes such as drinking, agricultural, industry and environment. In case of not paying attention to this challenge especially wind erosion in the study area, this case study especially dried beds for lakes can play as sources for generating dust particles. Therefore, the findings of this research can use by managers to mitigate negative effects of this phenomena.