نشریه پژوهش های آبخیزداری
پیاپی 130 (بهار 1400)

Water shortage in the arid and semi-arid regions has necessitated subsurface dam construction for groundwater storage. The aim of this study was to determine the appropriate locations for subsurface dam construction using a set of field, laboratory and software methods in the arid and semi-arid regions of the provinces of Kohgiluyeh and Boyerahmad. Six axes were selected by examining the topographic maps and the drainage network. The most important factors influencing the subsurface dam construction were selected. Using the average expert opinion benefitting from a questionnaire and employing the FUZZY-AHP method, suitable places for subsurface dam construction were prioritized. Considering the geophysical studies, the characteristics of the affected strata were determined. The results of prioritization of suitable locations for subsurface dam construction showed that the Tang Nayab with a weight of 0.41 holds the top ranking. The study of the results of the most important factors affecting in subsurface dams construction indicated that water supply and bed-rock with a combined weight of 0.25 is the most effective factor in subsurface dam construction. The results of geophysical surveys also indicated that the alluvium strata had an electrical resistance of 300 to 400 ohm-meter. The results of geophysical surveys indicated that the alluvium thickness in selected site is 5 m.

It is very complex and difficult to fully understand the relationships in watersheds due to the heterogeneity and non-linear nature of hydrological and erosive behaviors. Therefore, the evaluation of watersheds requires a modeling process. After introducing the features of the eWater Source software as a management modeling environment for watersheds, two rainfall-runoff models of the GR4J and the IHACRES were compared to simulate the runoff of the Chel-Chay Watershed in the eWater Source environment. Chel-Chay Watershed, with an area of 256 square kilometers is located in Province of Golestan. In order to simulate the rainfall -runoff, the position of the watershed, sub-watersheds, stations, watershed outlet, operational units (based on land use map) and the watershed waterway network was simulated using the digital height model (DEM) in the Source environment. The GR4J and the IHACRES models were used. In this rainfall -runoff models, the continuous time series data were considered in the daily time steps. The time series of the daily precipitation of the years (2001 to 2010), and the daily evaporation and transpiration (during the same period) were used to implement the models. The models were implemented in the eWater Source environment. The discharge data for the period (2001-2010) were used to calibrate the models. The accuracy of the flow simulation based on the Nash-Sutcliffe criterion for the GR4J and the IHACRES models in the calibration period (2001-2010) were 0.79 and 0.73, and in the validation period (2011-2015) were 0.76 and 0.68, respectively. Therefore, it may be concluded that these models performed well in the simulation. The evaluation of results indicates that the GR4J model performs better than the IHACRES model for simulating the daily flow. Due to the high capabilities of the eWater Source software, this environment is recommended as a management model for the discharge of watersheds.

The social capital is based on the relationships of social actors and their communication type within a network. For this reason, the emphasis is on creating a coordinated network between different organizations in order to the successful implementation of development programs. The importance of this issue as a platform for participatory management of watersheds is also emphasized by international organizations. This study investigated the effectiveness of organizational network of the carbon sequestration project in the Tilabad Watershed in promoting the social capital. Using the social network analysis method, 30 organization and institutions related to this project were surveyed in the Azadshahr county of the province of Golestan regards the communication network. The data collection tool was a questionnaire, in which the linkage of information exchange for natural resources management was measured between the concerned organizations before and after the implementation of the carbon sequestration project. Data analysis was performed using the UCINET software, in which the algebra of matrices was used to estimate network parameters and the graph theory was employed to show the relationships. The results indicated that the implementation of the carbon sequestration project led to an increase in organizational network parameters such as size, density, reciprocity, transitivity and closeness centrality. Moreover, the geodesic distance mean and network centralization were decreased. These findings suggest an improvement in the institutional cohesion and an enhancement in the communication network stability. Therefore, the implementation of the carbon sequestration project has reinforced the social capital in the organizations' communication network; thus, it provided better conditions for carrying joint action plans in the Tilabad Watershed.

An accurate assessment of the carbon changes in different ecosystems may be used as key indicator in estimating changes in land degradation at a global scale. The goal of this study was investigate the trend of land degradation by examining the trend of changes in the gross primary production, climatic parameters (temperature and precipitation) and its relation shies with the climatic data in the 2001-2017 period in different land use system in the Province of Fars. The annual gross primary production data were extracted from the MOD17A2 8-day MODIS sensor, and the climatic data were collected from 15 stations in the region and interpolated. The slope of changes in the gross primary production, temperature and precipitation, and the correlation between the gross primary production and temperature and precipitation in each land use were investigated. The results indicated that the highest percentage of the gross primary production was obtained for the shrub land, farmland, bare land, grassland, urban and built up land and water bodies, respectively. Examination of the slope of the changes showed that overall trend of changes in primary the gross primary production was increasing, while the temperature and precipitation trend were increasing and decreasing, respectively. The reason for this is the groundwater use by farmers to provide the needed water for irrigation, resulting in an increase in the gross primary productivity. Percentage of the changes in the gross primary production, temperature and precipitation in different land uses over the mentioned time period indicated that the trend of positive changes of the gross primary production in bare land use was 78.24%, farmland was 32.32%, grassland was 81.14%, shrub land was 85.89%; in the savannah it was 100%. We observed an increasing and decreasing trend for the temperature and rainfall over this time period, respectively. Based on the results, the correlation in bare land, savanna and shrub land is mostly influenced by precipitation, whereas farmland and grassland are affected by temperature. In general, despite of increasing temperature and decreasing rainfall, the gross primary production increased in the farmland, which indicates that such expanses are susceptible to land degradation and desertification.

Understanding the flooding phenomenon and its effective factors is an essential prerequisite of its control and management. This phenomenon is influenced by hydrological, climatic and physiographic factors, as it has always been one of the most important issues in hydrology. Using the overlapping of the climate and the border maps of the country, catchments of each climatic region were demarcated. Furthermore, 314 hydrometry stations with a common period (1976-2011) in six climatic zones were selected. The instantaneous peak discharge value was calculated for a 50-year return period. 15 hydrological, climatic and physiographic parameters affecting the flood severity, namely average altitude, catchment area, the Gravelius coefficient, the slope, the main river length, the annual average precipitation, the average number of rainy days, the base flow index (BFI), the hydrograph recession coefficient (K), the curve number (CN), the permeability and the flow duration curve indices (FDC indices) of, Q2, Q5, Q10, Q20, were calculated for each catchment. The factor analysis after data standardization was performed in order to select the most important independent factors affecting flooding severity for each climatic region and the regression between the Flooding severity index and the selected factors in different climate zones were extracted and analyzed. Results indicated that the parameters used in all of the climatic regions explained more than 74% of the variance of the data. Common parameters in the first class of effective factors in all of the climatic zones were different flow parameters of (BFI, K, FDC indices), along with some parameters that were related to the intrinsic characteristic of the catchment, such as the CN and permeability. The flow exceedance value of, Q2, Q5, Q10, Q20 in all of the climatic zones were ranked first and may be recommended for estimation and prediction in the ungauged catchment. The normal distribution of errors and the coefficient of Durbin Watson (between 1.5 and 2.5) reflect the confidence of the regression equations to estimate the Flooding severity in the ungauged catchments in the different climatic zones.

Landslides are one of the major types of slope instability which cause enormous financial losses and casualties; therefore, it is imperative to consider them in the study of geomorphology, erosion and sedimentation in important watershed. The aim of the present study was to investigate and rank the landslide susceptibility using a random forest method in the Sadat Mahalleh Watershed, Sari. Elevation from the sea level, geology, land use, slope (degree, direction, shape and length), distance from linear elements such as faults, streams and roads, normalized difference vegetation index and slope form were considered as effective parameter in the landslide occurrence. Zoning landslide sensitivity was achieved by coding in the R and GIS10.3 soft wares. In order to determine the weight of each of the factors and classes effective in zoning the landslide sensitivity and validation of landslide potential prediction maps, the abundance ratio method and the receiver operating characteristics (ROC) were used. The results indicated that among the effective factors, vegetative cover and land use, had the most paramount impact on the landslide occurrence in the study area. A landslide sensitivity map was prepared using the random forest method by dividing into five class, namely: very low (3.85%), low (5.38%), moderate (23.08%), high (50%) and very high (7.69%) sensitivities. Validation of the results of the landslide sensitivity zoning maps, using the relative factor characteristics index diagram, indicated that the area under the curve (AUC) for random forest method was 0.709 and its standard error was 0.10. It is reasonable to claim that the forest method provided an acceptable accuracy for mapping the landslide sensitivity. A landslide sensitivity map provides prone complete and accurate information for natural resource managers to detect the landslide areas.

Recognizing watershed problems and investigating the causes which arose them is the most fundamental step in watershed management plans, which results in identifying key management responses in each watershed. Therefore, it is necessary to thoroughly analyze the problems and determine management strategies before developing operational plans to solve them. The aim of this study was to analyze the environmental problems of the Gorganrood Basin to determine the main managerial responses. Identifying and analyzing the main environmental problems resulted in developing management responses for the region. To prioritize different components of the DPSIR, a Likert questionnaire filled with expert opinions and the Friedman test were used. The results indicated that four driving forces, namely climate change, population growth, management structure, and rules have caused 25 pressures on the Gorganrood Basin resources. The most important pressures were part-thinking organizations, incorrect agricultural expansion and excessive exploitation of water resources. These pressures, in turn, have caused 10 disturbed states, the most important of which are water resources depletion, flooding and soil erosion. These situations have 13 adverse impacts, the most important of which are flood damages, reduced downstream water rights and reduced public confidence in the government agencies. To improve the situation, 28 management responses were presented, of which the most important are integrated watershed management, land use planning and proper organizational structure. The overall result is that cause and effect analysis using the DPSIR framework provides an appropriate conceptual infrastructure, which is a prerequisite for developing the Basin's operational management plan. Therefore, it is suggested that executive organizations identify suitable responses by using this approach before developing operational plans for each watershed.

Soil conservation aimed at reducing runoff and erosion is essential for the optimal and sustainable use of natural resources. Rice straw can be used as affordable and available organic mulch, especially in the north of the country. Effects of two coverage levels of 40 and 70% of rice straw on some hydrological components of 0.5×0.5 m plots with two types of soil with sandy-loam and sandy-clay-loam textures were investigated. Considering three replications for each treatment, 36 plots with a slope of 18% were placed under a rainfall simulator with two rainfall intensities of 50 and 90 mm h-1. The results showed that rice straw in all studied treatments had a significant effect (P≤0.01) on increasing time to runoff initiation and its end time, reducing runoff coefficient and runoff volume after the end of rainfall. The Maximum incremental changes in time to runoff and maximum decrease in runoff coefficient was in the 70% of straw treatment on the sandy-clay-loam texture with 353% increase and 108% decrease compared to control treatment, respectively. In general, 40% of straw coverage was more effective in reducing runoff in the sandy-loam soils, while the effect of 70% of straw coverage on runoff reduction was higher in the sandy-clay-loam soils. In other words, by increasing the percentage of clay, a higher covering percentage is needed to prevent the destruction of surface soil aggregates, thereby increasing permeability and reducing the runoff coefficient.

Sediment accumulation is one of the major factors that reduce the beneficial life span of artificial reservoirs. Conservation and improving vegetative cover conditions may reduce sediment accumulation. A framework for implementing the PES was proposed assuming that the cost of soil and vegetation cover conservation may be considered as an investment in water supply through economic incentives, consisting of vegetative cover change projection, erosion and sediment transport modeling, reservoir sedimentation estimation, and the PES scheme design. Based on the results of increasing the amount of total sediment production from 486637.6 m3/yr in the current situation to 564217.5 and 658925.4 m3/yr, respectively over the next 20 years, and reduction of the useful lifespan of the Shirin Darreh reservoir (17.3%), the minimum payment for ecosystem services was considered 104 million Rials/yr. Furthermore, the volume and the total value of sediment control services provided by the vegetative cover was also determined by considering a complete degradation of the vegetative cover scenario and opportunity cost of 740535.5 m3/yr and 3.7 billion Riyals. Furthermore, the maximum payment was also estimated by considering the total value of the sediment control services and the estimated net present value of range conservation to be about 3.9 billion Rials/yr.

Floodwater spreading plays an important role in restoring and enhancing the vegetative cover, improving soil fertility, groundwater recharge and desertification control. These have been achieved in some of the arid and semi-arid regions of Iran. Flood water spreading as a corrective measure, in soil seed bank composition and diversity was assessed in the Gareh Bygon Plain, Fasa, the province of Fars. Soil seed bank was evaluated in the water-spreading tracts, water-spreaders planted with Atriplex lentiformis harvesting and the control area (without water-spreading). Sampling of soil seed bank was carried out at a 0-10 cm depth prior to the initiation of seed growth in December 2017, and the composition of the soil seed bank was determined by the germination method in the greenhouse. The results indicated that from 42 species identified in the soil seed bank, 40, 40 and 24 species were present in the three areas. Water- spreaders, water-spreaders planted with Atriplex lentiformis harvesting and the control tracts, respectively. The highest species diversity and richness indices were obtained in the area under water-spreading. The RDA analysis showed that the species composition and functional groups of soil seed bank of the study area were affected by flood water spreading practices and Atriplex lentiformis harvesting planting. Furthermore, the soil seed bank density of plant functional groups was affected by water-spreading. The results indicated that 35 years of floodwater spreading has positively affected the composition, diversity and functional groups indices of the soil seed bank.