Introduction: Understanding hydrological phenomena is essential for the optimal use of water resources. Surface runoff is an important part of the hydrological cycle. Accurate runoff estimation can make a significant role in water engineering and the proper utilization of resources for the various uses of agriculture, drinking, hydropower and the environment. Therefore, the use and development of accurate and reliable methods to model the runoff of the catchments are essential. One of the new methods of runoff calculations is cellular automata. Cellular automata is a fundamental method for simulating complex systems.Methodology: In cellular automata, the lattice space is divided into a number of cells and creates a cellular space (Fig2). A set of cells adjacent to the central cell is called a neighborhood (Fig1). In the runoff production process, the cell state is the water level, which is the sum of the cell height and water depth. The height of the cell is determined from the digital elevation model and the determination of water depth is controlled by the effective precipitation at the present time step and the balance between inlet and outlet flow at the last time step. The transition rules in the cellular automata model determine the behavior of cells at different time steps and define the future state of the cell. The first transition rule determines which neighboring cell can get water from the central cell at each time step (Fig3). The second transition rule is used to calculate the amount of flow to neighboring cells, in which the Manning equation is used. The first and second transition rule applies to all cells at each time step and as a result, the output flow from each central cell to its neighbors is determined. In the general view, each central cell is a neighbor of other cells, as a result, a third rule must be used for calculating the total flow for each cell. The evaluation of the cellular automata model is performed using the statistical indicators of correlation coefficient and root mean square error and Nash-Sutcliffe efficiency coefficient.Results and Discussion: First, the runoff is simulated on a uniform rectangular surface and the results of the cellular automata model are compared with the results of the Akan analytical solution. In order to evaluate the efficiency and accuracy of the cellular automata, the statistical parameters of the models were calculated. The results showed that the cellular automata model has high accuracy and efficiency (Fig 5). Then runoff in the Con catchment is simulated. This catchment is located in the northwest of Spain. (Fig 6). The results showed that the cellular automata model has been able to simulate runoff well in the catchment surface (Fig 7). At the outlet, the discharge is calculated based on the cellular automata and compared with the observed discharge. The results of the cellular automata model are shown with three different time steps (Fig 8). So far, various mathematical models for rainfall-runoff estimation have been proposed. In integrated models, the whole catchment is considered as a unit. These models have a simple structure and appropriate computation time, but are accompanied by many assumptions and the spatial distribution of variables is not considered. Therefore, integrated models are not suitable for large catchments. In semi-distributed models, the catchment is divided into a number of sub-catchments. In these models, important features of the catchment are shown, but for each sub-basin, moderate data is considered and the exact spatial distribution of data is not considered. In distribution models, spatial distribution data is considered, but the time required for computation and modeling is high. Therefore, it seems necessary to develop methods that have a simple structure and high accuracy at the same time. Due to the accuracy of the results and the ability to access the required information anywhere in the catchment, the cellular automata model can be used to predict runoff.Conclusion: The results showed that the cellular automata model has a high accuracy compared to the Akan analytical solution. Also, in simulating the runoff of the con catchment, the runoff network at the catchment surface was well simulated. Comparing the computational discharge results from the cellular automata model and observational data, the values of the correlation coefficient, mean the square root of error and Nash-Sutcliffe coefficient were 0.99, 0.11 and 0.97. As the result, due to the accuracy of the results and the ease of implementation, the cellular automation model can be used to predict runoff in catchment without data and reliable results can be achieved.

One of the factors impacting quality of water resources is pollution due to urban storm runoff during first stage of storm runoff and is commonly called "firsflush". At this stage the pollution load is rather high. However, if this pollution is properly controlled and managed, the size of the required treatment facilities will be considerably reduced. The surface runoff pollution in the city of Isfahan is high and necessitates the implementation of some control system. For this purpose, ten rainfall events were studied during fall and winter between 1999 and 2000. The data were gathered through grab sampling from Sio-se-pol bridge watershed. Statistical methods were used for analyzing data. The pollution load distribution vs. runoff volume was investigated.The results indicate that total solids (TS), suspended solids (SS), organic compounds and lead concentration exceeded discharge standards. TS, SS and organic compounds were more significant during the firstflush. SPSS (a statistical software package) analyses showed that there is a correlation between TS in the firstflush and runoff flow rate.Statistical analysis of the results indicated that rainfall depth and duration increase SS washoff during first stage of runoff. Also it was found SS washoff increases with increasing average discharge during firstflush.The results also indicated a correlation exists between the SS in the firstflush and the rainfall depth, event maximum intensity, average intensity, rainfall compounds and rainfall characteristics. Finally, an equation was suggested to predict pollution loading of runoff during firstflush.

Surface gravel cover is an important factor for contoroling of soil erosion in dry area specially in area that plant can not grow because of excessive dryness and salinity. The objective of this study was investigation effect of different surface gravel cover on runoff and sediment yeild. For this porpose, 36 field plots with 20 meter length and 0. 5 meter width at 3 percent slope were constructed in research field of agriculturev faculty, Shahrekord university. Treatments were including four level gravel cover (0, 10, 20 and 30 percent) and three surface flow rate (2. 5, 5 and 7. 5 L min-1) at three replications that expriment was done in a factorial with randomized complete block design. The results showed that as increasing surface gravel cover decresed the runoff rate and sediment yield significanty (p<0. 001) in comparision with control treatment as linear and exponential, respectively. Aso, statisticaly comparision of the effect different gravel cover on runoff and sediment indicated that the effective gravel cover on runoff and sediment was different with increasing surface flow rate, as suitable gravel cover for surface flow 2. 5 and 5 L min-1 was 20 percent and for surface flow 7. 5 L min-1 was 30 percent gravel cover.

Declining pervious areas is one of the most important effects of land use changes and replacing natural watersheds with urban zones. This phenomenon increases the surface runoff and the possibility of urban floods. In recent years, the unprecedented expansion of urbanized areas of Mashhad City has caused an increase in runoff potential. Since, on the other hand, there is a serious lack of water resources for the city, a comprehensive study on urban surface runoff and methods of managing the runoff has become a serious necessity in Mashhad. In this study, after sub-basin delineation, based on the available data, first the rainfall-runoff process for a number of urban and natural sun-basins was calibrated using HECHMS rainfall-runoff model. Then, the volume of surface runoff was computed for the whole city of Mashhad. Finally, management methods of surface runoff especially in terms of runoff storage were considered both technically and economically. The results showed that despite the high volume of produced runoff, runoff management merely based on storage is not reasonable due to spatial restrictions. In other words, the cost ratio for storing and using each cubic meter of runoff is very high and economically not feasible. Consequently, the main approach in runoff storage in Mashhad needs to focus on utilizing the potential of existing lakes and reservoirs. In addition, the other important approach should be based on storing the water released from Golestan Dam located 5 km of the southwest of Mashhad.

High concentrations of heavy metals in soil are toxic to plants, animals, and human beings. The present study was performed in the region in the south of Tehran, which is exposed to pollutants and where the runoff from urban areas is being extensively used for irrigation. Soil samples were collected from 8 stations. The soil distillation method was used to extract heavy metals from the samples and their concentrations were determined using atomic absorption to decide whether the concentrations of such heavy metals as Pb, Cd, Zn, Cu, and Ni exceeded hazardous limits requiring protective measures to be taken. Results showed that the concentration gradients of all the parameters studied increased in the north-south and west-east directions. The average concentrations of Pb, Ca, Zn, Cu, and Ni were 61.12, 1.42, 61.07, 25.85 and 29.22 mg/kg, respectively, in the northern stations, and 76.40, 2.62, 172.05, 69.85 and 37.40 respectively, in the southern stations. Comparison of which might have been the cause for the wider distribution of heavy metal concentrations in this region. Moreover, the runoff passing through the deepest parts of the southern region and the extensive application of the flow for irrigation could have caused the higher accumulation of heavy metals in this region. Our findings also indicated that it is necessary to treat surface runoff and to avoid runoff application for irrigation as measures for preventing environmental pollution.

Introduction Arid and semi-arid areas often have sparse and scattered vegetation cover. In many arid regions of the world, open spaces between plants are occupied by particular living organisms called biological soil crusts (BSCs) or biocrusts. BSCs are the dense population of living organisms such as cyanobacteria, algae, fungi, lichens, and mosses in different proportions that live on the soil surface or within the upper few millimeters of soil. The aim of the present study was to investigate the effect of biological soil crusts on surface runoff quality in hillslopes around Ajigol Wetland in the Golestan Province of Iran.   Materials and Methods The study area is located in the northern part of Golestan Province. Elevation in the study area ranges from 7 to 32 meters above sea level. The topography of the area is gentle and the land surface is composed of loess deposits. According to the climatic conditions, the research area is classified as arid and semi-arid regions. Due to a lack of rainfall, high evaporation, and uneven distribution of rainfall throughout the year, as well as high soil salinity, it has low-growing and weak rangeland plants. The vegetation in the area is composed mainly of annual grass species scattered heterogeneously. They often appear after rain events and have a short growth period finishing the life cycle in one season. In this research a field rainfall simulator was used. First, field visits were conducted to select places for positioning rainfall-runoff simulation plots in different types of biocrusts. To eliminate the effect of slope on runoff processes, locations were selected whose slope was around the dominant slope of the region (around 20 %). Rainfall-runoff simulations were carried out using a rainfall simulator over 1 x 2-m plots with and without biological soil crusts. The intensity of the simulated rainfalls was about 80 mm h-1 and the duration of each simulation was 30 min. The plots were positioned over five different types of surface cover including 1) dominant moss cover, 2) dominant lichen cover, 3) mixed (moss + lichen) cover, 4) dominant shrub (Artemisia spp.) cover, and 5) Bare land. Sampling and measurement of some runoff quality variables (sediment, electrical conductivity (EC), acidity (pH), color, and Total Dissolved Solids (TDS)) were conducted at 15-minute intervals during the simulation, plus one more sample from a mixture of runoff of the whole simulation. For some other water quality variables (organic carbon, nitrate, phosphorus, and potassium) measurements were made only at the end of the simulation from the total runoff mixture. The data were analyzed using graphical methods (plots) and statistical tests: analysis of variance (ANOVA), Kruskal-Wallis, and Tukey’s test.   Results and Discussion The results showed that sediment concentrations were significantly (P ˂ 0.05) lower for biocrust-covered plots compared to the plots without biocrusts. Extreme differences were observed for the bare soil. EC, pH, color and TDS values also had significant differences between different covers. For organic carbon, phosphorus, nitrate, and potassium, no significant differences (P ˂ 0.05) between covers were detected by statistical tests though some notable differences were discernible on plots. The origin of runoff EC is mostly inorganic substances and it is caused by natural and human-induced pollution. There was a significant difference (P ˂ 0.05) between shrub-covered plots and plots with a combination of moss and lichen. EC for the shrub cover (Artemisia spp.) was found to be significantly higher than the mixed moss and lichen cover. The reason can be attributed to the increase in permeability and soil moisture in BSC dominated areas. Increased infiltration of water by biocrusts causes salts and ions to move deeper into the soil and this reduces the salinity of upper soil layer and surface runoff. With regard to runoff color, a significant difference (P˂ 0.05) was observed between bare soil and the other cover types. By producing polysaccharides and viscous materials, BSCs preserve and stabilize the soil surface materials and reduces the transport of metal ions (such as iron and manganese), decayed plant materials, organic matter, and animal waste as the main factors for the coloration of runoff. In contrast, more detachment and transfer of materials from bare soil have caused the runoff to become thicker and darker. The amount of sediment concentration from bare land was higher than shrubland and biocrust covers. For example, the average sediment concentration in the runoff from plots of bare land was about three times that of Artemisia plots. Another notable point was the large difference in sediment concentration between bare soil plots themselves. The reason for this was attributed to the presence of remaining roots of annual plants in the bare soil plots, which influence runoff and soil loss.   Conclusions Overall, the results indicate the major effect of BSCs on runoff quality. So, taking proper measures to protect them and prevent their destruction is of great importance for soil and water conservation as well as water quality preservation in downstream wetlands. Therefore, it is necessary for government agencies to pay more attention to BSC-covered hillslopes around the Ajigol Wetland so no more damages are imposed on these fragile unique resources. As no comprehensive map of BSC covers the study area is present, it is recommended that such a map be prepared using satellite and drone imagery. Then, by combining the results of this study with the information obtained from mapping and generalizing it to the entire region, it is possible to make an overall estimate of the effect of BSCs on the water quality of downstream wetlands which is necessary for better-informed planning and decision-making. Exclosure and cover protection measures to prevent physical damages caused by human activities need to be implemented for the BSC-covered areas so they can continue their function as living mulch and protect soil from water and wind erosion.

Background & Aim: Urban runoff is one of the most valuable and renewable water resources in many arid and semi-arid parts of the world. Understanding how to use these resources is very important. The purpose of this study was to determine the physical, chemical and biological properties of surface runoff in Zahedan for irrigation uses. Methods: The present work was a descriptive cross-sectional study. Grap sampling was taken at two rainfall events at the intersection of Azarakhshi and Pasdaran crossings. The samples were examined for physical, chemical and microbial parameters according to the standard water and wastewater testing methods and qualitative irrigation parameters. The results were compared with Iranian and FAO environmental standards for irrigation uses. Results: The mean COD and BOD5 parameters were 359 and 56. 6 mg/l, respectively and the mean heavy metals of nickel, zinc, cadmium, lead, copper, chromium, iron in solution were 6. 8, 66. 66, 1, 2. 2, 8. 93, 5. 1 and 92. 5 mg/l, respectively. The mean total coliforms were 38333/33 MPN/100ml. The average of irrigation quality indices including SAR and Na% were 20. 1 and 59. 2%, respectively. Conclusion: The results showed that the surface runoff of Zahedan in many parameters including heavy metals such as nickel, zinc, lead, copper and chromium, turbidity, TSS, TDS, sodium, total coliform CODs and CODs are above the maximum permitted DOE and FAO limits for irrigation usage.

Despite of soil disturbance, transfer to the laboratory and preparation inside the plots which themselves lead to lower validity of the results, the experimental study on runoff and erosion at plot scale with many research advantages are inevitable. However, there has been less attention to evaluate the effects of soil preparation on runoff and sediment variables. The present study was therefore conducted to compare surface runoff in two undisturbed (natural) and disturbed (during various steps of preparing soil for laboratorial studies) soil conditions. To achieve the study purposes, 1×1 m-plots were considered in a slope with sandy-clay-loam soil and gradient of 18% under simulated rainfall with three intensities of 40, 60 and 80 mm h-1. The study slope was located in the vicinity of Kodir village in upper Educational and Research Forest Watershed of Tarbiat Modares University. The time-to-runoff in the output of each plot was recorded and the runoff volume and coefficient at five three-minute intervals was subsequently measured. The results showed that the average time-to-runoff, runoff volume and coefficient were significantly (p£0.01) increased 2.29, 3.45 and 2.79 times, respectively due to the soil disturbance which clearly indicated the impossibility generalization of laboratorial runoff and erosion results to natural conditions without considering the effects of soil disturbance. The results showed the synergistic interaction of soil disturbance and rainfall intensity on time-torunoff and antagonistic interaction on runoff volume and coefficient.

Karstic lands are one of the important resources in Iran and in the world. Therefore, investigation of these catchments are necessary for better using. In this article, the main objective is to compare hydrological characteristics of two types of catchments, calcareous rock and noncalcareous rock formed. Vehrgan catchments is a karstic watershed that mostly covered by limestone, and is located in Zagross mountain ranges on the Chahar-mahal-bakhtiary, Esfahan and Lorestan states boundaries, compared with a nonkarstic catchments, namely Golpayegan catchments that having a 160 kilometers distance from west of Esfahan and north of Vehregan in view of maximum discharges, runoff coefficient, specific discharge and relation between maximum instantaneous discharge and maximum daily mean discharge with the similar climate, catchments area, slope and annual rainfall. This study indicates that runoff coefficient is 1.28 for Vehregan's karstic catchments and is 0.32 for Golpayegan that is a non-karstic catchments. Specific discharge for vehregan catchments on a concurrent period is 0.0174 and for Golpayegan is 0.051 discharges for vehrgan catchments on a concurrent period is 0.0174 and for Golpayegan is 0.051 m3/sec/km2. Relation between maximum instantaneous discharge and maximum daily mean discharge in the water year 49-69 for vehregan karstic catchments is between 1.001 and 1.76 with an average of 1.45. This relation for Golpaygan catchments for that period is between 1.01 and 2.01 with an average of 1.38. The main result of this study is that application of rational and empirical formulas for karstic catchments is unreliable.