پژوهشنامه مدیریت حوزه آبخیز
پیاپی 29 (بهار و تابستان 1403)

Soil erosion, a significant form of land degradation, poses severe challenges to humanity in different ecosystems. It serves as a comprehensive index for evaluating the development and sustainability of land management programs. Assessing the status and spatial extent of soil erosion has become crucial in developing countries. Biological management, a recommended and effective means of controlling soil erosion in the early stages of all processes, offers a practical solution. Biological methods, such as minimum tillage operations and limited intervention in nature, prove to be more cost-effective and efficient than structural measures. Despite these advantages, biological measures have not received adequate attention in soil erosion control. This research addresses this gap by applying biological management in the Kilanbar Watershed (Kermanshah Province, Iran), demonstrating its effectiveness and cost-efficiency.

The layers of elevation from sea level, aspect, and slope steepness were prepared and combined in the geographic information system (GIS) software to prepare 38 land units. In the Kilanbar Watershed, 14 land units with the ability to perform biological management measures were extracted based on the expert and technical opinions of the watershed manager and considering different bases to improve the performance and decision-making of the units with an area of less than 300 ha. The Kilanbar Watershed is located in Ravansar City, west of Kermanshah Province. The study area is approximately 10798 ha. The highest and lowest elevation points of the watershed are 2183 and 1388 m above mean sea level, respectively. The mean annual precipitation, temperature, and relative humidity are 533 mm, 11.4 °C, and 45.1%, respectively. The status of soil erosion in each land unit was completed based on the scoring of the BLM form based on the visual and expert opinions, and a map of the erosion pattern was prepared in the land units. Ambrotropic and hyetographs were drawn using the 30-year precipitation and temperature data of the Ravansar synoptic station to determine the periods of drought and wet conditions and to identify suitable plants with the characteristics of the region. A climatic–agricultural map was prepared and integrated into the GIS using meteorological station data (temperature, precipitation, evaporation, and transpiration), and plant species were selected according to ecological expectations for watershed biological measures.

According to the BLM form results, one and eight land units are in partial and low erosion conditions, respectively, and five other land units are in medium erosion conditions. According to the erosion pattern map, the majority of the studied area, about 70% of the watershed, is in a low and medium erosion state, which naturally confirms the high ability to use appropriate biological measures to control soil erosion. According to ambrothermic and hyetograph measurements, June to September were dry months, and precipitation changes were more significant than temperature changes from October to May. According to the climatic–agricultural map, the region is divided into five classes. Class 4 (4819.3 ha) and Class 1 (364.83 ha) had the largest and smallest areas, respectively. Finally, the zoning of suitable rangeland species in the watershed showed that rangeland species of Asteragalus ascendes, Avena fatua, Picnomon sp., Achillea millefolium, Bromus tomentellus, and Hordum blubosum dominantly covered the region. Based on the study results, appropriate plant species were introduced for the studied watershed. Accordingly, conservation and reclamation measures were recommended to improve land productivity and ecological conditions and avoid land use changes for the study area. The essential measures include vegetation in rangeland ecosystems aiming at preventing the role of the canopy cover from directly impacting raindrops on the soil surface, increasing water infiltration in the soil, stabilizing soil aggregates due to roots extension, increasing grazing capacity and livestock production, and increasing its efficiency and productivity with time.

The findings of this study hold significant potential for the Kilanbar Watershed. The proposed biological erosion measures, tailored to the ecosystem's unique conditions, are effective, low-cost, and environmentally compatible. They offer a sustainable solution for managing soil and water resources in various ecosystems. Implementing these measures can significantly reduce soil erosion in the watershed, particularly in areas with low to moderate erosion status. This research is an essential initiative in applying biological erosion measures in the Kilanbar Watershed, demonstrating that soil erosion can be effectively and practically controlled in approximately 67% of the watershed through biological methods in the critical land-use areas of rangelands and agriculture. It is important to note that applying biological erosion measures requires comprehensive and integrated investigations, considering the different parts of the ecosystem. With these findings, the proposed approach in this research can be extended to other watersheds across the country, particularly those with slight to moderate erosion status, while maintaining the principle of comprehensiveness and respecting the unique conditions of each watershed.

Climate change directly impacts hydrological components, water resources, and watershed outflow. Calculating the amount of possible changes in rainfall and runoff will play an important role in the policy-making and planning of water resources under climate change conditions. In this research, runoff simulation in the eastern watersheds of Mazandaran province (Talar, Tajan, Nekarood, and Babolrood) was investigated under the impact of climate change in the future period (2021-2040).

In this research, one of the atmospheric-ocean general circulation models, named HadGEM2, was used under climate scenarios (RCP 2.6 and RCP 8.5) to investigate climate change. The Lars-WG model was used for the downscaling of climate data during three stages of data calibration, data evaluation, and meteorological data generation for the future period. This purpose was achieved using the daily data of rainfall, maximum and minimum temperatures, and sunshine hours of the selected stations of four watersheds in the current period (1997-2016), and the model was implemented for the base period. After ensuring the ability of the Lars-WG model to simulate meteorological data by comparing the data produced by the HadGEM2 model and the observational data of the base period, this model was implemented to generate future data using climate scenarios (RCP 2.6 and RCP 8.5). The daily values of the climate data of rainfall, maximum and minimum temperatures and sunshine hours were produced and simulated for the next 40 years (2021- 2060). Runoff simulation in the future period and the effect of climate change on runoff were investigated with the IHACRES hydrological model, which is a continuous conceptual-dynamic model for simulating rainfall-runoff at the watershed scale, using climate scenarios. For this purpose, the daily data of rainfall, mean temperature, and discharge of the current period (1997-2016) in four watersheds were introduced into the IHACRES software. Then, the 1997-2008 and 2009-2016 periods were selected for calibration and validation, respectively, to determine the ability of the IHACRES model to simulate future runoff. After calibration and validation, the climate data produced by the HadGEM2 model were introduced into IHACRES, and the daily series of discharge was predicted for the future period (2021-2040). Then, the annual average of the observed discharges in the current period and the simulated discharges in the future period under the RCP 2.6 and RCP 8.5 scenarios, as well as the 20-year average runoff in the stations in the future period, were compared and evaluated with the observation period.

The results of the climate change investigation showed that mean monthly minimum and maximum temperatures in all months of the future period would increase in all four watersheds in both scenarios RCP 2.6 and RCP 8.5 compared to the current period (1997-2016). Compared to the current period, the mean monthly rainfall in both scenarios does not have a constant trend and is different in various months. The results of the runoff simulation show that the changes in the discharge of the watersheds under the effect of climate change are not constant compared to the discharge of the current period. This could be attributed to the inconsistency of the trend of changes in the precipitation of the future period compared to the current period. Despite the increase in the average rainfall, the discharge will decrease in some years in the future period, which can probably be related to the increase in temperature in the future period due to climate change. Despite the decrease in the average rainfall of that year, the increase in discharge could be caused by, for example, the possibility of heavy rains or showers in that year, thereby increasing the amount of discharge. Compared to the current period, the 20-year mean of the predicted discharge has decreased in the selected stations (Talar, Tajan, and Nekarood watersheds) in the future period for both scenarios. In the station considered for the Babolrood watershed, however, this value has increased in the RCP 2.6 scenario compared to the current period. In the Polsefid station of the Talar watershed, the simulated discharge under the RCP 2.6 and RCP 8.5 scenarios was equal to 6.18 and 6.12 m3/s, respectively, which shows a decrease compared to the observed discharge of 7.41 m3/s. In the Soleimantange station of the Tajan watershed, the predicted discharge under the RCP 2.6 and RCP 8.5 scenarios was equal to 7.33 and 7.29 m3/s, respectively, which has decreased compared to the observed discharge of 9.82 m3/s. In the Sefidchah station of the Nekarood watershed, the simulated discharge under the RCP 2.6 and RCP 8.5 scenarios was equal to 3.85 and 3.72 m3/s, which reveals a decline compared to the observed discharge of 4.10 m3/s. In the Babol station of the Babolrood watershed, however, the discharge under the RCP 2.6 scenario was predicted to be equal to 11.40 m3/s, which has increased compared to the discharge (11.34 m3/s) during the observation period. Under the RCP 8.5 scenario, it was simulated with a value of 11.22 m3/s, less than the observed discharge.

In general, the impact of climate change on water resources is one of the major challenges facing water resources planners and can have serious consequences for ecosystems and communities. Based on the findings of the research and the importance of climate change effects on the hydrological conditions of the watersheds in the study area, it is necessary to apply appropriate policies for the sustainable management of water resources.

Depending on rainfall systems and conditions influenced by unprincipled human activities, floods cause a lot of damage to natural resources, settlements, and projects every year. Hydrometric stations are often destroyed during floods or small watersheds lack hydrometric stations, which means that the estimation of runoff and maximum flood discharges requires a suitable method to calculate runoff and flood values in these basins. Prevention of this damage is doubly important when the study area overlooks places with a high density of settlements and urban facilities that can threaten the lives of many residents. The amount of runoff in each sub-basin of the watershed overlooking Malayer City was estimated in this study.

The watershed overlooking the city of Malayer with an area of 14,700 hectares is stretched from the north to the northeast of the city. The processing of digital elevation models identified five sub-basins overlooking the city and field visits. The curve number method was used to estimate runoff height and flood volume in each sub-basin. The most intense rainfall event (88 mm per day) with a return period of 30 years was designed as rainfall, considering the amount of previous rainfall 5 days before this event with a cumulative value of 45.2 mm. To calculate the physical parameters of the watershed in this study, topography, geology, vegetation, soil, and land use maps were digitized using a geographic information system. Simultaneous maps of land use and rainfall were provided using Sentinel-2 images, containing 13 spectral bands and a spatial resolution of 10 meters. Utilizing the SCS method, the layers of land use, vegetation, and soil hydrological groups were combined to produce a curve number map. The value of the curve number was corrected for the wet condition based on the rainfall 5 days before and the location of the basin in the previous wet conditions. A weighted curve number approach for each sub-basin was compared with another approach based on the arithmetic mean of the curve number for each sub-basin, as well as a weighted runoff height approach for each curve number. Kirpich's method was used to calculate the concentration time of each sub-basin. In the next step, using the maximum daily rainfall data from the Malayer synoptic station in the statistical period from 1991 to 2021, the rainfall height values were converted to runoff height using the SCS relationship, and then the peak flood discharge was calculated for each sub-basin.

The lack of permanent vegetation and the presence of annual grasses are among the reasons for the high potential of the sub-basins in runoff production. As a result, the average curve numbers of arithmetic and weighted average methods are 79.09 and 81.46, respectively, which shows the high capacity of the basin in producing runoff. Converting curve number values to peak flood height and flow using two commonly used methods of curve number calculation and comparing it with the results of the weighted runoff height calculation approach for each curve number in the working units of the study area showed no significant difference. Finally, the runoff height maps and the peak discharge of each sub-basin were drawn. The northern sub-basin of the basin with an average runoff height of 44.32 mm and a peak discharge of 168 m3/s has the highest participation in flood discharge toward the city of Malayer, and sub-basin 4 in the south-eastern part of the basin has the least participation in flood generation. The results of the relationship between the area and runoff height showed that the basins with a larger area did not necessarily contribute the most to the occurrence of floods in all three calculation methods of the curve number and runoff height. Other factors also play a role in these results, such as the extent of rocky outcrops and reduction time of concentration due to the high slope as one of the reasons for this problem. The formation of the longest watercourse in the basin with a length of 16314 meters under Sub-basin 3, which has the highest peak flood flow after Sub-basin 2, is one of the discussed technical points that can handle the rapid discharge of the peak flow of about 100 m3/s. However, the study of its longitudinal slope of about 2% indicates the high risk of flooding caused by the lack of evacuation in rains with a high return period, which in turn is a serious risk for the threats caused by floods in the southeastern part of the city. The intersection of the end part of the main waterway with the exit of other sub-basins and the collection of runoff under the upstream basins are other problems that increase the risk of flooding in the downstream areas.

It is suitable to use the curve number method to estimate the amount of runoff produced in the basins overlooking the settlements that do not usually have hydrometric stations. Because of its low-density pastures and rain-fed agriculture, the watershed overlooking Malayer has a high potential for runoff production.

Debris is one of the important phenomena of slope movements in mountainous areas. Harsh climatic conditions and the availability of tectonic and geological structures in the central Alborz Mountain heights have caused a significant amount of debris to form on the slopes. Studying this process by relying on two opportunity and threat patterns is particularly important. Therefore, the current research tries to analyze the susceptibility of the occurrence of the Haraz Valley debris flow in the range of Plour to Baijan by providing a suitable index to prioritize the factors affecting the formation and expansion of debris to achieve its more accurate zoning.  

The effects of six layers of information, including lithology, height, slope, aspect, distance from the fault, vegetation, and land use, were investigated on the occurrence and spread of debris flow. First, the debris location in the area was identified using the geological map of Damavand, with a scale of 1:100,000 and Google Earth images. Then, the distribution map of the debris was prepared after field survey and recording points by a GPS device and transferred to the GIS environment. Maps of independent and influential variables on the spread of debris, including lithology and distance from the fault, were prepared from the Damavand geological map, and the height, slope, and direction of the range were prepared using the ASTER digital elevation model. The vegetation and land use maps were prepared from the national coverage map of Iran by processing Sentinel images on the Google Earth Engine Cloud platform. In the next step, the distribution map of the debris was combined with each map of the affecting factors, and the weight of each class of independent variables was obtained based on the density area model. Then, a zoning map of the susceptibility of the spread of debris was prepared in five classes of very high, high, moderate, low, and very low susceptibility. The average effective weight of the deposit susceptibility index was also calculated to determine the prioritization of affecting factors and prepare a more accurate map for the zoning of the expansion of debris.  

The analysis of factors affecting the spread of debris in the studied area using the density area model shows that Melafir stone units (weathered basalts) have the most weight among all the stone units and all factors affecting the spread of debris in the region. After that, biogenic limestone, alluvial defenses, and Lar Formation are more important factors. The investigation of the elevation factor shows that the frequency of debris increases from 2100 meters up, and the elevation class of 2400-2700 meters is more sensitive. In terms of the slope factor, most of the debris in the region was observed in the slope between 10 and 40 degrees, and the largest deposit cover is related to the slope layer of 20-30 degrees. The calculation of the area density of the debris in different aspects shows that the northwest and north slopes have the most weight and susceptibility. The process of freezing and melting snow is evident in the destruction of rocks and the creation of most of the debris on these slopes. Examining the distance from the fault also showed that the frequency of debris is significant up to a distance of 1000 meters, and the highest weight of this layer, based on the density area, belongs to the zero-500-m layer of the faults. In addition to transmitting seismic stresses, faults cause the penetration of water caused by melting snow into rocks and are influential in destroying rocks and causing debris. In terms of vegetation and land use, pasture lands are the most susceptible to debris. The results of the statistical analysis of the density area and preparation of the regional zoning map showed that 5, 21.15, 29.78, 29.53, and 14.54% of the area of the region have very high, high, medium, and low susceptibility, respectively, to expand debris. According to the Debris Susceptibility Index (DSI) model, land use, lithology, and slope have the highest priorities with average effective weights of 21.04, 20.12, and 18.72, respectively, and are the main factors controlling the spread of debris in the area. The factors of slope, elevation, aspect, and distance from the fault were the next priorities.

In the current research, the distribution of debris in different classes of independent variables was analyzed using the Density Area Model, and the importance of each class of parameters affecting the spread of debris was determined based on the weighting of the layers relative to each other. To evaluate the effic iency of the results of the density area model and verify its performance, a zoning map of the expansion of debris was prepared using the DSI model. The evaluation of the accuracy of the models using the empirical probability (P) shows that the density area and DSI models are suitable for zoning the susceptibility of debris in the area with probabilities of 0.79 and 0.80, respectively. The layers of high susceptibility to very high expansion of the deposit cover about 26% of the area, which is considered an environmental resource from one point of view. Hence, it can be exploited as a sedimentary deposit for use in engineering structures by forming a volume reserve, and from another point of view, it is a potential risk in agricultural fields, residential areas, and hydraulic structures.

Soil erosion is one of the global problems that threatens water and soil resources. Protecting and recovering bare and uncovered soils, as well as diverting surface runoff from the soil, are an efficient method for reducing soil erosion in sensitive and erosion-prone areas. Among the activities to prevent soil erosion are to maintain the natural vegetation of the area and stabilize bare and uncovered soils with the help of temporary or permanent methods. The use of erosion control blankets is a soil bio-engineering method that can effectively reduce runoff and sediment and increase slope stability. Therefore, the current research aimed to temporarily stabilize soil using protective covering treatments, such as jute, straw, wood chips, Festuca grass cover, and nano zeolite super absorbent, to reduce the amount of runoff and sediment.

The study area is the Darabkola Forest (the educational-research forest of Sari University of Agricultural Sciences and Natural Resources), with an area of  about 2612 hectares located in the southeast of Sari City between 52° 14′ E and 36° 28′ N. To measure the amount of runoff and sediment in the Darabkola Forest, plots with dimensions of 70 x 50 cm and a depth of 10 cm were created using galvanized sheets. Then, plots were placed on the ground with a slope of 3%. Erosion control blanket treatments made of jute filled with wood chips, straw, and nanozeolite superabsorbents were prepared and located in the plots, as well as jute cover, jute cover with Festuca grass, and Festuca grass. Rain simulation tests were conducted for each sample (30 minutes with an intensity of 50 mm.h-1) and the amount of runoff from the plots was measured at 5-minute intervals using a graduated cylinder placed at the bottom of the plots. Sediment concentration was measured by weighing the samples after settling the runoff and passing it through filter paper. Sediment concentration was calculated by dividing the amount of sediment by the volume of runoff. Data were analyzed using one-way ANOVA for seven treatments. Duncan's test was used to compare the means. Pearson's correlation analysis was also used to investigate the relationship between runoff and sediment concentration in runoff.

The results of statistical analysis showed that the highest amount of runoff (0.77 mm.h-1) belonged to the control treatment, and the lowest amount was recorded in the treatment of straw and the Festuca herbaceous species (0.24 and 0.27 mm.h-1, respectively). Overall, the straw treatment reduced the amount of runoff by 69% and the Festuca herbaceous species treatment reduced it by 64% compared to the control plot. The results of sediment concentration revealed 63% and 52% decreases in the amount of sediment in the samples belonging to the treatment of jute cover and jute cover together with Festuca species, respectively, compared to the control plot. The highest sediment concentration was measured in the control sample (7.13 g/ml). The presence of Festuca in the soil reduced the sediment by 2%, which shows that the presence of a herbaceous species such as Festuca does not considerably reduce the sediment concentration compared to the other treatments such as jute. Examining the coefficients obtained from Pearson's correlation analysis between runoff rate and sediment concentration in runoff for different treatments indicated that the stabilizer addition to the soil reduced sediment and reduced surface runoff in some treatments. A positive and significant correlation was found between runoff and sediment in wood chips, straw, Fesuka, and nanozeolite treatments, while a negative and significant correlation was recorded for Jute + Festuca and the Jute treatment.

This research demonstrates that the use of erosion control blankets with combinations of different materials, such as straw and stubble, nanozeolite, and wood chips, along with the Festuca grass cover, can reduce runoff volume and reduce soil erosion and waste, especially in forest road trenches containing soils without vegetation. Moreover, grass cover (such as Festuca) increases water permeability in the soil and prevents soil loss. Therefore, using these erosion blankets can reduce soil erosion around forest roads.

Landslides are among the environmental hazards that annually cause significant human and financial losses in extensive mountainous regions of our country. Therefore, identifying the important and influential factors in the occurrence of this phenomenon can be used as a practical tool to reduce potential damage. Consequently, recognizing the environmental factors affecting the occurrence of landslides in forest road networks is of great importance. Due to its mainly mountainous topography and extensive tectonic activity, Ramsar County has a natural potential for widespread landslides within the communication network area. The objective of this study is to assess the susceptibility of landslide occurrence in the Ramsar County area by considering influential factors, especially forest road networks, and utilizing Geographic Information System (GIS) capabilities.

To achieve this goal, the locations of landslides were determined using field studies, historical reports, and Google Earth images. A total of 95 landslides were identified in the region, which were divided into two groups for modeling (70%) and validation (30%). Sensitivity analysis of landslide occurrence was carried out based on criteria such as slope, slope direction, land use, distance from residential centers, terrain curvature, precipitation, temperature, erodibility, elevation, vegetation cover density, lithological units, soil texture, drainage density, distance from roads, and topographic wetness index. Land cover density and vegetation greenness were calculated using 16-day products from Landsat 8 satellite in Google Earth Engine, and the final output was calculated using weighted regression methods in GIS and Excel software. Receiver Operating Characteristic (ROC) curves were employed for model evaluation and validation.

The most significant factors affecting landslide susceptibility include soil type, slope of the terrain, vegetation cover, geology, hydrogeological flows, topography, precipitation, and communication lines. Susceptibility zones and landslide density are more pronounced in peripheral areas of transportation corridors. The construction of extensive structures, side effects of road construction, and the disruption of natural terrain balance for road construction and expansion have led to continuous occurrences in these areas. The correlation of parameters influencing landslide occurrence with the landslide distribution layer indicates that approximately 76% of landslides have occurred in slopes ranging from 11 to 38 degrees. Erosion of slopes by high-velocity runoff flows has caused more than 63% of landslides to occur within 500 meters of watercourses. Alongside the three main factors of soil type, natural slope, and slope erosion, landslide occurrence is influenced by road reconstruction and development without considering slope stability principles. More than half of the observed landslides in the area have occurred in a sequence of rock, shale, sandstone, and volcanic rock, accompanied by coal layers. The discontinuity of the landslide layer with the distance from the road indicates that landslide occurrence up to a distance of 400 meters from the road has been due to direct effects of road construction and embankment activities, disrupting the balance of slopes adjacent to the road, gradually decreasing with the distance from the main road. The results show that the Frequency Ratio model provides an acceptable accuracy with an area under the curve (AUC) of 0.76 for landslide susceptibility mapping. The final susceptibility map indicates that class 5 with very high susceptibility covers 13.06% of the total area, class 4 with high susceptibility covers 16.35%, class 3 with moderate susceptibility covers 22.32%, class 2 with low susceptibility covers 27.46%, and class 1 with very low susceptibility covers 20.79%. Consequently, 31.79% of the total area is at risk of severe landslides. Considering the final map and the close relationship between road presence and landslide occurrence, it can be stated that the northwestern and eastern forest roads of Ramsar County are more exposed to landslide occurrence.

It appears that the removal of vegetation cover, alteration of watercourse routes, modification of natural terrain slopes, and excavation of soils and rocks for road construction in the area have led to landslide occurrences around forest roads. The marginal areas of transportation corridors show a significant discrepancy in susceptibility coefficients, highlighting the potential importance of landslide occurrence in these regions. It can be concluded that providing appropriate recommendations and strategies to reduce landslide risks, improving area management, and implementing preventive measures in this region are highly necessary. This study demonstrates that through accurate analyses and alignment with environmental conditions, effective measures can be taken to reduce the effects of landslides and enhance the stability of operational areas. Therefore, a combination of geological, hydrogeological, topographic, and geographical information analyses can be used as an effective tool for studying, predicting, and managing landslide risks in mountainous regions.

Large-scale and regional planning requires observed data on environmental variables, such as runoff and suspended sediment load from watersheds. Data is fundamental for generating information and knowledge, and scientific management of a system is impossible without a monitoring and measurement plan. Management of watershed systems and water resources is no exception to this axiom. With ongoing trends in socioeconomic development, climate change, increasing pressure on natural resources and watersheds, and, consequently, an increase in floods and sediment yield, there will be a greater need for more accurate information about sediment and runoff processes in the near future. Many tools and instruments for measuring runoff and sediment components have been produced and marketed by a number of foreign companies. However, their cost is very high in Iran, on the one hand, and a device that measures both components at once is very rare, on the other hand.To carry out simulations that are both accurate and efficient, it is essential to have access to sufficient and reliable data and information for verification and validation purposes. In the field of water resources and watershed management, data and information are considered to be crucial tools. By providing important insights into the management of water resources, the availability of data and information can help enhance the efficiency and optimization of water usage, prevent natural hazards (such as floods and droughts), manage water quality, and improve the management of water supply and demand. Therefore, this study aimed to design and construct an automated flood and sediment load-monitoring device with the ability to record the runoff height of watersheds and a planned sampling of runoff for measuring suspended sediment using cheap sensors and tools.

This study presents an innovative device designed to monitor runoff discharge and suspended sediment sampling. The device has been constructed and installed at the outlet of the sub-basin under study. A regular cross-section was constructed at the outlet to facilitate the installation of the device, which enabled the monitoring of the runoff hydrograph of the sub-basin outlet and suspended sediment load sampling. In this research, analog hygrometer sensors were used to measure the height of runoff with 3 cm intervals (measurement accuracy of 3 cm). DC pumps with valves were used to collect the sediment sample, which created a vacuum in the sampling container and caused the runoff sample to be transferred into the container. To evaluate the device's capabilities in real and natural conditions, it was installed at the outlet of a sub-watershed in the eastern loess lands of Golestan province, located upstream of Qapan Oliya village in the Kalaleh district for two years to record the hydrograph of likely flood events and take runoff samples at the user-defined depths of flood (two samples at depths of 20 and 60 cm in rising limb and one sample at a depth of 20 cm in recession limb of hydrographs). The samples were stored in 0.5 liter containers, and the user was informed by sending an SMS to replace the filled containers with empty ones. It is noteworthy that the device under consideration facilitates the collection of runoff samples at any frequency and at any height for research requirements. The device boasts a remarkable advantage in the form of its SMS notification feature, which keeps the user informed about the monitoring site and equipment status, including runoff sampling, power outages, and battery status. The device incorporates a built-in battery that remains active during power outages in the electricity network to record flood events. Additionally, the user can communicate with the device via a mobile phone at any time and receive SMS updates on the device's operating status, such as power, battery, memory level, and event registration. Furthermore, to ensure accurate rainfall data recording, a WatchDog tipping bucket rain gauge has been installed within the studied sub-basin.

During these two years, only three rainfall events leading to runoff and flooding occurred in this sub-watershed, and the designed device successfully recorded the hydrograph of all three events and informed the user. In each of these recorded flood events, at least two runoff samples (one sample in the rising limb and one sample in the recession limb of the hydrograph) were collected and stored by the device to be transferred to the laboratory to determine the suspended load. The present study has demonstrated that the automated runoff and sediment monitoring device, which has been specifically designed to measure a range of parameters such as flow rate, water level, and suspended sediment load, represents a valuable and practical tool for those seeking to monitor runoff and sediment at the outlet of watersheds.

Data and information play a vital role in water resources and watershed management. The availability of such data and information in the management of watersheds and water resources helps enhance water use optimization and efficiency, prevent natural disasters such as floods and droughts, manage water quality, and improve water supply and demand management. Therefore, the prototype of the designed device shows that this device has a good capability for the industrial production of an inexpensive runoff and sediment monitoring tool to scientifically manage small-scale watersheds.

Simulation of the rainfall-runoff process for estimating runoff due to rainfall is an important step in planning and management of natural resources and water resources, especially in watersheds without hydrometric stations. However, this process has its own complexities and several affecting factors such as precipitation factors (amount and intensity of rainfall), vegetation cover (type of cover and cover density), soil factors (soil texture, soil initial moisture, and permeability), and land management quality. This study aimed to provide a model for simulating the rainfall-runoff process using artificial neural network (ANN) modeling and runoff data of field plots.

The study was executed on a slope at Guilan University using clay-loam soil in a repetitive way, with paired plots subjected to different vegetation and land management treatments. The amount of rain was measured after every rainfall using a storage rain gauge. Runoff values were estimated by plots, and from the difference between precipitation and runoff values, the initial loss values at the surface of each plot were calculated for each precipitation event under different soil moisture conditions. The total precipitation of the previous five days was estimated as the previous soil moisture. Regarding the agronomic management method, two patterns of plowing in the slope direction and plowing perpendicular to the slope direction were used and compared to patrolling native rangeland species. The changes in slope, soil texture, and soil properties were negligible due to the limits of the area, thus soil was not used as an input affecting runoff. Since the aim was to evaluate the effect of vegetation cover and agronomic management on runoff production, it was necessary to provide the same conditions for the level of paired plots to neutralize the effect of soil. To model the obtained data, they were divided into two categories: educational and subject data. The parameters of runoff values were considered the output of the model, and the precipitation values, percentage of rangeland and tree canopy, precious soil moisture, and percentage of leaf litter were regarded as the optimal inputs of the model. The land slope was estimated by surveying. Vegetation cover and leaf litter percentages were measured using the ratio of vegetated area to the total plot and microplot area. It is difficult to quantitatively determine the type of coverage, but the height of the vegetation was also considered due to the simulation of the effect of raindrops, rain spraying, and tree foliage.

The amount of reserve was actually very small due to the limited area of plots. Based on statistical analysis, the rainfall and previous soil moisture factors have a positive relationship with runoff production. Vegetation and leaf litter have an inverse relationship with runoff values. Finally, the most important factor in controlling runoff production is vegetation cover (R2 = -0.71). The highest efficiency in controlling runoff production was observed in a plot with a rangeland cover of 100% canopy cover. Vegetation somehow determines the amount of leaf litter and humus in the soil. Tree species have also been limited in controlling runoff reduction, and if rangeland cover is located under the canopy of trees, it will cause double efficiency in reducing runoff production. However, there is generally no maximum pasture cover under trees or forest lands. The results showed that the amount of runoff production can be reduced by up to 10% due to the limited number of trees due to vegetation. In previous studies, this effect of forest cover varied between 40% of dense forests and sparse forests. The results also show that both factors of the type of leaf litter and the amount or percentage of leaf cover are influential in controlling runoff. Regarding the effect of plowing patterns, the results show that plowing and strip cultivation in the direction perpendicular to the slope direction lead to a decrease in the runoff rate, more runoff penetration, more moisture retention in the soil, and better conditions for vegetation growth and development. Finally, these cases will lead to a significant decrease in runoff production. A comparison of the measured runoff in these two plots in different precipitation events has indicated that the plot with plowing and perpendicular cultivation in the direction of slope after the complete establishment of vegetation can be up to 50% more effective in reducing runoff production. The results of the trial-error method in the neural network model indicate that the rainfall values, the type of vegetation cover, and the percentage of vegetation canopy are the optimal inputs for simulating runoff values. The results also show that the hyperbolic tangent transfer function and the LM learning technique are the best options for the optimal structure of networks. Neural network training in two stages showed that the used model was highly efficient in estimating runoff values. Based on the validation results, the MLP is an efficient network for simulating runoff values or the rainfall-runoff process. Moreover, a comparison between the simulated and the observed values of runoff in the experimental phase showed a good agreement between the simulated and the observed values. The values of MSE = 0.97, R2 = 0.004 and MSE = 0.91, R2 = 4.2 were obtained in the training and testing phases of the model, respectively, and, finally, a high-performance model was presented to simulate the rainfall-runoff process. The result of the modeling process showed that rangeland cover had the highest efficiency in controlling runoff.

Vegetation characteristics, such as vegetation type and density, are the most important factors controlling runoff in sloping lands. In addition, land management, cultivation patterns, and plowing methods are other important factors. Therefore, it is possible to estimate the total losses and initial loss based on soil characteristics, land slope, and previous soil moisture and to select suitable cultivation patterns or vegetation types for runoff control or planting and model their yields during the rainfall-runoff process. A tested model based on the neural network can also be a tool for estimating runoff values on a monthly and annual scale based on the precipitation data of meteorological stations. The model can be used to simulate the effect of different vegetation scenarios on runoff production or to estimate runoff based on the precipitation of meteorological stations.

The coefficient of hydraulic roughness of rivers is one of the most important factors in the planning, design, operation, and maintenance of water resources projects in river engineering studies. The value of the hydraulic roughness coefficient varies in diverse and complex conditions of rivers and is affected by various factors, usually in hydraulic models the roughness coefficient shows the most sensitivity compared to other parameters. A correct estimate of the roughness coefficient improves the understanding of flow hydraulics and river conditions. Despite many efforts, the inability to accurately estimate the roughness coefficient and the use of Manning's constant value (n) are the main error factors in flood simulation and flow depth calculation. The flow roughness coefficient is typically not constant and changes dynamically as the flow depth changes. The best way to determine the roughness is to measure the flow rate and calculate Manning's n through the inverse solving of Manning's equation. The present study mainly aims to determine more precisely the roughness coefficient of the Sanij River upstream of the Faizabad hydrometric station.

The studied area in the current research is the Sanij watershed, 30 km from Yazd city in Taft city, Yazd province. This basin has an area of 153,173 square kilometers. To achieve the objectives of the research, after conducting field studies, the Faizabad hydrometric station at the outlet of the Sanij watershed was used to collect the required flood discharge and ash-flow data in the study area; Therefore, the hydraulic radius and the value of Manning's roughness coefficient were estimated through the inverse solving of the corresponding equations and the determination of other hydraulic parameters such as velocity and slope. The slope was measured with an inclinometer and a leveler.

The lowest value of the n is equal to 0.034, corresponding to a discharge of 180 m3s-1 , while the highest value of the Manningʼs roughness coefficient is equal to 0.119, corresponding to a discharge of 2.083 m3s-1 . As the discharge decreases, the roughness coefficient increases. The function of the roughness coefficient in relation to the discharge (with R2  = 0.80) indicates their inverse and significant relationship. The function of the hydraulic radius in relation to the discharge (with R2  = 0.944) indicates that the discharge and hydraulic radius have a direct and significant relationship. The roughness coefficient has an inverse lower less-significant relationship with the hydraulic radius. Every flood creates different roughness levels with different sedimentation rates; therefore, Manning's roughness coefficient will vary depending on variations in particle diameter. Usually, the channels or rivers of dry areas are temporary, in the descending branch of the hydrograph and at the end of the flood, larger parts remain on the surface of the bed, and it causes errors in the estimation of Manning's roughness coefficient based on experiments and local visits. The apparent error is caused by the larger diameter particles remaining on the surface of the bed and the carrying of fine particles by the flow. On the other hand, during the flow, the orientation of the sediments is generally in line with the direction of the flood, which creates the least hydraulic roughness; But with the reduction of flood intensity and the remaining of coarse-grained particles, in addition to the increase of hydraulic roughness, the random roughness of particles, which plays an effective role in Manning's roughness coefficient, increases. In flows where the flow depth is lower than D90, or smaller than the diameter of large pebbles in the bed, Manning's roughness coefficient reaches its highest value under static-hydraulic conditions, and inflows with greater depth From D90 due to special hydrodynamic conditions, the lowest value of Manning's roughness coefficient was observed. In other words, at high flow rates, the relationship of the roughness coefficient on the entire flow is reduced; therefore, with the increase of the flow depth, the value of n decreases and the hydraulic radius increases. This phenomenon is mostly seen in rocky channels and rivers. The current research showed that in the rivers of dry and rocky areas, we usually encounter overestimated values of Manning's roughness coefficient due to the presence of large pebbles in the bottom of the dry bed. This phenomenon can be seen especially in floods with lower discharge and the cause of this can be related to the reduction of hydraulic roughness in the bed during the flood flow. This phenomenon can be effective in overestimating or underestimating the roughness coefficient.

The results show that the roughness coefficient changes from 0.034 to 0.119 in the study range and has an inverse and significant relationship with discharge (R2  = 0.8). Moreover, the roughness coefficient has an inverse relationship with the hydraulic radius (R2  = 0.59). The roughness coefficient is not constant and changes in different flood events. Discharges with a depth less than D90  are those in which Manning's roughness coefficient reaches its maximum value of 0.11. In this study, the lowest Manning's roughness coefficient was observed in discharges with a depth greater than D90  and a flood height greater than 50 cm, as in the discharge of 115m3s-1 , the roughness coefficient “n” decreased to a limit of 0.034. The roughness coefficient is unstable in different events, because during the passage of the current or in the ascending and descending branches of the flood hydrograph, depending on the speed and power of the flow, the bed granularity is dynamically changing, and Manning's roughness coefficient (n) is instantaneous. It changes. During the peak flow, it is difficult to understand the hydrodynamic roughness coefficient and it can lead to overestimation or underestimation of the roughness coefficient; Therefore, it is better to consider this case to achieve more accurate values of roughness coefficient in river engineering studies

Rivers are complex systems in which all kinds of chemical, biological, and physical processes take place and change under the influence of various factors and variables in terms of dimensions, shape, direction, and pattern. The changes that occur in the conditions of rivers have many effects on the river ecosystem. Carrying out any activity in rivers requires knowing the rules governing the river and predicting the river's reaction to it to avoid the related harmful consequences. It is usually difficult to understand the processes of rivers by measuring hydraulic parameters on a real scale. On the other hand, sediment transport modeling is also a very complex and difficult matter because the information that is used to predict bed changes is basically uncertain and the theories used are experimental and highly sensitive to a wide range of physical variables. The high costs of laboratory equipment and the limitation of using measuring devices are among the other reasons that limit the use of physical methods and lead experts to mathematical and numerical modeling to simulate the flow inside water channels. Continuous change is one of the governing principles of every river, and a change in flow conditions also causes changes and displacement in other geometric characteristics of the river. Because rivers are often moving in their alluvial beds, different types of bed forms have been formed in the river bed due to the shear stress in the bed. The formed shapes cause a part of the surface water flow in the river to enter the porous environment below it and return to the surface water flow after oxygenating and feeding benthic organisms. This type of currents that arise from the mixing of surface current and subsurface current in the porous environment under and around the river is called hyperic current. The surface, subsurface, and underground water systems and exchanges between them are in three levels: point, interval, and watershed. Fallen tree trunks are common structures in rivers. One of the factors in creating hyperic exchange is the presence of a pressure gradient at the border of surface flow and the porous medium. The pressure gradient is caused by various factors such as obstacles in the flow path or bed forms. Depending on the magnitude of these factors, they will affect the amount of exchange and the depth of the hyperic expansion. The first step in understanding the hyperic phenomenon and its application is to examine changes in the characteristics of this area, including the amount of current exchange, depth, and retention time. Therefore, the objectives of this research are to investigate the effect of natural obstacles created by tree trunks on hyperic characteristics and the effect of the arrangement of natural obstacles created by tree trunks on hyperic characteristics.

The current field research was carried out in the Garambadesht River of Gorgan in the summer and winter of 2021 to investigate the effect of fallen tree trunks on the river path as a natural flow barrier in different tree trunk thicknesses (30, 60, and 90 cm). As one of the most important sources of drinking water for the city of Gorgan, the Garmabadesht River, originates from the slopes of Yazdaki Mountain at a point 27 km southeast of Gorgan and continues to flow northward. Then, it passes through the high and complex heights and enters the eastern plains of Gorgan. To carry out the present research, piezometers were installed in the upstream and downstream of the tree trunks and then evaluated using a numerical model in the Comsol software environment, compared to the simulation of the hyperic flow to estimate the amount of exchange flow.

This study obtained convincing findings regarding the correlation between piezometer observational data and numerical simulation results. A 91% correlation was obtained between piezometer observation data and simulation results, which was used as a basis to investigate the computational exchange flows from the numerical model. The findings showed that the amount of exchanged flow in blocked conditions was higher than in non-blocked conditions. This issue shows that tree trunks can have a significant impact on the dynamics of hyperic flow, an important consequence of which is the direct impact on river ecosystems, especially in relation to the preservation of coastal vegetation and aquatic habitats. The investigation of the retention time of the flow lines in three obstacle states shows that the increase of the obstacle in the flow path has increased the retention time because the flow lines have become deeper and their length has increased with the increase in the height of the obstacle, thereby increasing the retention time.

The results indicate that the maximum amount of equilibrium discharge occurs in the case where the thickness of the tree trunk is 30 cm in winter. The amount of exchange flow with obstruction is higher than that without obstruction. The equilibrium flow rate in winter is higher than the exchange flow rate in summer. The investigation of the penetration of flow lines shows that the penetration rate of flow lines has increased with the increase in the thickness of the barrier. Considering the vastness of the research field, it is appropriate to conduct more research to discover more understanding of its mechanism.

One of the important effects of global warming is the increase in extreme atmospheric phenomena, the most important of which are sudden changes in temperature, excessive heat, abnormal cold, heavy rains and floods, drought, and dust caused by the drying up of wetlands. Changes in climatic components due to climate change have impacted the intensity and frequency of extreme rainfall events and, subsequently affecting society and the natural environment. Therefore, examining the future modifications of different precipitation indices is more necessary to implement management plans, especially for Iran, which needs progress in climate modeling studies aiming at improving knowledge about climate change and its effects on the whole country. In this study, changes in the trend and breaking point of rainfall-based indices were studied using the CMIP6 series model under three optimistic, medium, and pessimistic scenarios in Mazandaran province for two periods: the near future (2021-2060) and the far future (2061-2100).

In this research, the spatiotemporal trend and breaking point of the precipitation in Mazandaran province (15 stations) were investigated in the future period from the precipitation data of SSP scenarios (126, 245, and 585) in the two 2021-2060 and 2061-2100 periods.  Using the R-Climdex software in the R software environment, the precipitation limit indices were determined for different scenarios and periods. Then, the trend and breaking point were examined using the Mann-Kendall, Sen, and Pettitt tests. Precipitation indexes were defined by an expert group under the supervision of the World Meteorological Organization as limit indexes and climate change indexes. After receiving the output of models and their micro scaling, data were grouped in the future period based on three scenarios in all studied stations. The daily rainfall indexes were extracted using R programming developed by Zhang and Yang at the Canadian Meteorological Service Climatic Research Branch. Therefore, 11 and 16 indices out of 27 existing indexes were related to precipitation and temperature, respectively.

Under the optimistic scenario (SSP126), the indexes of the number of consecutive wet days, days with heavy rain, and very wet days in the eastern half of the province will increase significantly. Based on the pessimistic scenario (SSP585), the profile of wet days and the annual amount of rainfall will decrease in different areas of the province. In terms of the occurrence of the breaking point, the daily intensity of precipitation and wet days will have a breaking point in the order of increasing in the 2060s, rising in 2061, and decreasing in 2051 in the eastern half of the region only in the pessimistic scenario of the profile of consecutive wet days. Under the other scenarios, however, no sudden changes will be observed in the data series. According to the median scenario, there will be no changes in precipitation indexes regionally, and only the daily intensity index of precipitation will increase in a limited number of coastal stations in the near future. Under a pessimistic scenario, however, changes in limit indexes will often be reduced so that the index of the number of wet days (with 1 mm rainfall) will decrease in the near future in most parts of the province with high intensity. The annual amount of rainfall on wet days in coastal and western regions, as well as two indexes of the number of days with heavy and very heavy rain, will decrease in the high stations of the western areas. However, the risk of flooding events may be reduced in the near future, and the probability of widespread droughts increases due to the reduction of wetness profiles in pessimistic conditions. In the distant future, precipitation indexes will not change significantly, and only the number of days with heavy rainfall will decrease in the high areas of the eastern province. In terms of sudden changes, there will be no sudden change or significant breaking points in the data series of all the precipitation indexes until 2100 by moving toward an optimistic and median scenario. Moving toward a pessimistic scenario, there will be an incremental change point for indexing the number of consecutive days at a few provincial stations for the 2070-2060s. The daily intensity of precipitation and the number of wet days (with 1 mm precipitation) will also experience a sudden incremental change in 2061 and a decrease in 2051 in the eastern half of the province, indicating a sudden increase in the intensity of downpours and a reduction of the number of days with low rainfall.

According to the results, it can be concluded that the study of the occurrence of severe meteorological events, including rainfall, as one of the main issues in the field of water resources, agriculture, and natural hazards in Mazandaran province, is necessary for long-term planning in various fields. Knowledge of the future perspective of extreme rainfall events can be used in soil, water, and agriculture management planning, especially in the economic development plans of the province.

Soil erosion and sedimentation are among the major problems and environmental challenges in watersheds. The sediment load in rivers causes numerous issues, such as sedimentation in dam reservoirs, changes in river courses due to sedimentation in their beds, reduced water carrying capacity in waterways and water transfer facilities, and changes in water quality for drinking and agriculture. These problems are of great concern to researchers and water resource managers as they can investigate sedimentation, erosion, and potential effects on biological processes. Therefore, it is essential to investigate and evaluate suspended sediment concentrations to determine water quality and hydrological functions. In this regard, the use of accurate, extensive, and cost-effective techniques, such as remote sensing, is invaluable for improving sedimentation estimation and, consequently, water quality assessment. Understanding the spatial relationships between upstream vegetation and sedimentation is crucial for the effective control and optimal management of water resources and soil. The present study aimed to determine the relationship between vegetation cover and suspended sediment concentrations in the Doab Mereg and Gamasiab watersheds.

In this research, the Sentinel-2 satellite data were investigated in the first step. If there were cloudy conditions, dust particles, or other radiometric problems, they were removed from the calculations. Then, factors such as band type (visible and infrared bands), river width (higher than the image pixel - 40 meters at the Doab station and 80 meters at the Polchehr station), separation power, and sensor location (10 and 20 meters) were considered to select the appropriate image pixel for obtaining the spectral reflectance of water. The pixel corresponding to the hydrometric station and its surroundings was selected to extract the spectral reflectance. Then, the suspended sediment concentration statistics of the Doab Mereg station located in the Qarasu River and the Polchehr station located in the Gamasiab River in the five-year period (2016 to 2020) were used simultaneously to investigate the correlation between the spectral reflectance of the Sentinel-2 image bands and sediment concentration. Next, the Normalized Difference Vegetation Index (NDVI) for the two May and June seasons was extracted using Sentinel-2 images. The relationship between vegetation cover and suspended sediment concentration recorded at the station and extracted from the images was estimated separately.

The results of the correlation analysis of suspended sediment concentration showed that the best result for the Doab and Polchehr stations belonged to band 4 (R2 = 0.86) and band 5 (R2 = 0.83), respectively. The suspended sediment concentrations varied from 0.17 to 76.45 and 0.44 to 118.86 mg/liter in the Doab Mereg and Polchehr stations, respectively. In the Doab station, the depth of the power state had the highest correlation coefficient between the observational data (recorded in the station) and the data extracted from the images. In the Polchehr station, it had a high correlation coefficient in both polynomial and exponential modes. The best values of the coefficient of determination (R2) of the normalized vegetation cover difference index for the Doab and Polchehr stations were 0.98 and 0.64, respectively. This means that the amount of sediment decreases with an increase in vegetation cover. The average values of the vegetation index for the Mereg watershed (0.35) and the Gamasiab watershed (0.28) show the relatively sparse vegetation in the area. The lowest average values of vegetation cover in the studied season (spring) were respectively equal to 0.11 and 0.21 in the Mereg watershed in June and the Gamasiab watershed at the end of May. The results of the regression test showed a strong and significant relationship between the density of vegetation and the amount of suspended sediment concentration recorded in the hydrometric stations of the two basins.

The results showed that six models were extracted for the studied area, which had acceptable and suitable R2 and error values. Among the obtained models, better results were obtained in the single-band model than in the case of using the band ratio. The highest correlations belonged to bands B2, B3, B4, and B5 in the Doab Mereg station, and to B4 and B5 in the Pol Cheher station. The highest R2 values obtained for the two stations were 0.86 and 0.83, respectively, in the exponential model. The results of this study show that Sentinel-2 can be used as a suitable tool to estimate suspended sediment concentrations with acceptable accuracy in small-scale basins and flood conditions, which has been confirmed in a number of similar studies. Sediment rate refers to the positive effect of vegetation on soil protection and the reduction of sediment production and transport within watersheds. In general, the results demonstrate that vegetation has been effective in the quantity and quality of the spatial changes in the sedimentation rate of the basins. In fact, the NDVI vegetation index, as a representative of the vegetation, can be successfully used to create a statistical model of the changes in the sedimentation rate. The revitalization of vegetation should be included in development plans.