Mahin Kalehhouei; Raoof Mostafazadeh; Abazar Esmali Ouri; Rahmani Naneh Karan, Fardin; Fazeli, Alireza; Nazila Alaei; Zeinab Hazbavi
Abstract
Introduction
The rainfall system of a major part of Iran is mediterranean, where the precipitation amount during the vegetation period is low. In addition, the occurrence of precipitation in the non-vegetation period or beginning of the vegetation period, which does not cover the surface of the earth ...
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Introduction
The rainfall system of a major part of Iran is mediterranean, where the precipitation amount during the vegetation period is low. In addition, the occurrence of precipitation in the non-vegetation period or beginning of the vegetation period, which does not cover the surface of the earth well, is one of the important reasons for water erosion in Iran. Since vegetation has a special role in soil erosion control and runoff retention, any change in the vegetation structure and pattern, which expresses the landscape pattern and function, can have a significant effect on changing hydrological processes. Therefore, the assessment of soil and water loss and the quantification of its relationship with landscape metrics provide key information for the development of water and soil quality management strategies.
Materials and methods
The current research was conducted to investigate the hydrological component changes with landscape metrics on 2 m2 plots using simulated rainfall at an intensity of 32 mm.h-1 in a part of rangelands of Ardabil County. At first, considering the type and percentage of vegetation as the main variable, eight groups of vegetation composition along with one group without vegetation (control) were considered with three replications. The composition (and percentage) of the vegetation from the first to the eighth groups, respectively, include low-height graminea predominance (45), the composition of dense bushes with graminea (43), bushes with low-height and medium-distribution (37), sparse bushes mostly with low and medium height (31), the composition of sparse bushes with graminea (56), dense bushes in upper parts (54), low-height bushes with very low distribution (15), and dense bushes with almost uniform distribution (56). After measuring the runoff and sediment at the plot outlets, different hydrological components were calculated. Then, plots with nine different vegetation combinations were imaged in three replicates before and after rainfall simulation. After transferring the images prepared from the plots to the Arc/Map10.8 environment, nine important landscape metrics were calculated.
Results and discussion
Changes in the mean patch density (4.43-26.90), largest patch index (54.16-86.75), edge density (17.12-107.38), landscape shape index (1.50-4.47), mean shape area (4.16-37.46), mean Euclidean nearest neighbor distance (0.00-1.65), landscape division index (0.19-2.31), mean patch shape index (1.24-22.85), and the effective mesh size (15.80-43.96) indicate their different influence from different percentage and composition of vegetation cover. Spearman's correlation matrix analysis showed a nonsignificant relationship between the mean soil loss, runoff volume, runoff coefficient, and sediment concentration with landscape metrics (r<0.26 and p-value>0.10). The small scale of the studied plots, the lack of diversity in the vegetation composition, and the uniformity in terms of vegetation height can be cited as the reasons for the lack of correlation. In general, groups with vegetation values above 50% had a better condition in terms of LPI, AREA_MN, and MESH, which indicates more connectivity and less degradation. The increase in vegetation cover and spatial heterogeneity above the landscape surface can change the path of sediment transport, reduce sediment connectivity, and lead to a decrease in sedimentation.
Conclusion
The obtained results are applicable in explaining the appropriate reference to optimize water and soil protection measures on the watershed scale. However, It is suggested that similar and more comprehensive research be done in different scales of erosion plots and even in the landscape (slope) scale so that by considering a wide range of vegetation, topography, climatic conditions, as well as successive rains, it is possible to compare the results, optimum selection of study scale, and finally planning to manage and protect vegetation and water and soil resources.
Somayeh Shariati; Abolfazl Azizian; Najmeh Yarami; Abbas Paydar Ardakani
Abstract
Rainwater harvesting using micro-catchment is one of the water resources development options in arid regions that can partly supply water requirement of rain-fed agriculture. Some operations can be performed for increasing the harvesting rainwater in micro-catchment. In this study, the effect of simple ...
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Rainwater harvesting using micro-catchment is one of the water resources development options in arid regions that can partly supply water requirement of rain-fed agriculture. Some operations can be performed for increasing the harvesting rainwater in micro-catchment. In this study, the effect of simple treatments including furrowing, clay cover, furrowing and clay cover and control treatments on runoff production were investigated in the form of a complete randomize design with three replications during 2014 and 2015 in Zarrin-Dasht region of Fars Province. Results confirmed the potential of rainwater harvesting in the region. The highest runoff coefficient was observed in control treatment as 6.5 and 9.3% in 2014 and 2015, respectively. Disturbing of surface soil (in various treatments except control) led to average reduction of 11 and 14% runoff amount and coefficient, respectively compared to the control treatment. Threshold Precipitation for Runoff Production (TPRP) was 1 mm in control treatment during two years of the experiment. In other treatments TPRP values reduced in the second year. In view point of the runoff amount and coefficient and also TPRP, control treatment is recommendable in the region. The catchment area varied almost between 15 and 150 m2, respectively, for supply water requirement of 300 and 600 mm with rainfall occurrence probability of 0.50 and 0.67 and runoff storage efficiency of 25 and 50%. In fact, micro-catchment area can be economically determined with crop type.
Khodayar Abdollahi; Samira Bayati; Mohammadali Nasr Esfehani
Abstract
Variations in the type of storms, distribution of rainfall over the basin and other influencing factors such as soil texture, land use types and slope classes leads to significant differences in the spatial distribution of water components. In this study, using the monthly scale data, including rainfall, ...
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Variations in the type of storms, distribution of rainfall over the basin and other influencing factors such as soil texture, land use types and slope classes leads to significant differences in the spatial distribution of water components. In this study, using the monthly scale data, including rainfall, groundwater depth, temperature, evaporation and wind speed, WetSpass-M model was used to analyze the spatial distribution of water components at the basin of interest in the south-east of the Karun Basin. The modeled results were calibrated to simulate the monthly streamflow. Considering the fact that the Vanak Basin is a mountainous area, the snow cover maps were introduced to the model in order to include melting process. Evaluation of the model's performance using the Nash-Sutcliff coefficient of 0.61 and 0.54 during the calibration and validation period, respectively showed that this objective function was acceptable. This means the model has produced acceptable outputs. After this step, the spatial distribution of runoff and groundwater recharge in relation to various land use and slope classes were studied. Analysis of the monthly spatial distribution of runoff and groundwater recharge maps showed that due to change in slope and land classes, the runoff coefficient has a significant impact on both groundwater recharge and runoff. In such a way that the forest areas and mild slopes have generated an average 138 mm annual runoff and 596 mm annual recharge accordingly, it means a lower runoff coefficient and higher recharge values. The highest montly recharge value was in February (82 mm in thin forests with the slops of less than 10˚). This may be used to provide a better understanding of the factors affecting the distribution of water balance components or help in the maintenance, management and planning of surface water and groundwater resources.
Raoof Mostafazadeh; Sonia Mehri
Abstract
Rainfall-runoff relationship is one of the most sophisticated hydrological processes which helps to understand the watershed hydrologic response assessment. The rainfall-runoff relationships of Ardabil Province watersheds were analysed to investigate the spatial variability of rainfall-runoff responses ...
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Rainfall-runoff relationship is one of the most sophisticated hydrological processes which helps to understand the watershed hydrologic response assessment. The rainfall-runoff relationships of Ardabil Province watersheds were analysed to investigate the spatial variability of rainfall-runoff responses using precipitation-runoff polygons technique at a monthly temporal time scale. Therefore, variations of recorded precipitation and runoff data were analysed over a period of 22 years from 1990-2011 in 20 watersheds of the Ardabi Province. According to the results, the maximum runoff coefficient is corresponding to Doostbeighlou Station by the value of 33%. The analysis of precipitation-runoff polygons reveals that the Arbabkandi, Polealmas, Samian and and Doostbeighlou watersheds had the higher amount of runoff coefficient. As well as, the hydrologic response of Shamsabad, Kozetopraghi and Ahmadkandi are similar and homogeneous in term of runoff generation. Based on the relationship between monthly runoff coefficient and the area, the highest correlation coefficient was observed in the March (0.92), and the lowest was assigned to August (0.0089). The larger the area of the polygon and the highest coefficient of variation is corresponding to Doostbeighlou and Samian watersheds. The distribution of the runoff coefficient over the months showed that the Hir and Ahmadkandi watersheds had the highest runoff coefficient in June and August which is related to the delay in runoff production. Based on the results, precipitation-runoff polygon technique is a suitable way to compare the hydrological response and changes in rainfall-runoff relationship of watersheds. It should be noted that the comlexity of rainfall-runoff process causes an overlapping in polygon portions and irregular shapes which caused a difficulty in interpretating of watershed response and needs much more furture researches.
Freidoon Soleimani; Aaollah Kavian; Karim Solaimani; Forod Sharifi; Kaka Shahedi
Abstract
The major issues that must be addressed in watersheds is correct estimating threshold from the rainfall events. According to the agricultural leveling land and irrigation and drainage network of study area is exposed to sourounding runoff destruction, so watershed management activities such as design ...
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The major issues that must be addressed in watersheds is correct estimating threshold from the rainfall events. According to the agricultural leveling land and irrigation and drainage network of study area is exposed to sourounding runoff destruction, so watershed management activities such as design of small-scale water structures, sediment control structures, implementing the management actions in vegetation, soil and land utilization is required to understand and estimate surface runoff threshold. The aim of this study was to determine the effect of soil conservation practices on runoff initiation time and runoff coefficient using rainfall simulator in the Arayez plain. For this purpose, a rain simulator with a metal plot that has a square meter area was used. The treatments consisted of natural soil (observed), polyacrylamide at two levels 3 and 6 grams per square meter (P3 and P6, respectively) and Parsian mulch (Pc) that were conducted in sandy clay loam and sandy loam soil with three replications. The rainfall intensities set up to be of 32 and 50 mm per hour in slopes 7.5 and 12.5 percent. For statistical comparison split split plot design was used. Least Significant Difference (LSD) method was used for comparison of means. Results indicated that the mean of runoff initiation time in observed treatment is higher than mulch treatments, it means which runoff begins later in observed treatment. Mulches of P6 and Pc have not significantly differences in runoff initiation time. Runoff initiation time in P3 mulch much earlier began than the other treatments. Also, results revealed that the mean of runoff coefficient in different treatments (observed, P3, P6 and Pc) have a significant differences, and belonged to separate group.
Majid Hosseini
Abstract
At present due to lack of proper utilization and management in non-renewable natural resources, most of the watersheds are in critical conditions. Since about 80 percent of Iran watersheds located in arid and semi-arid climatic conditions, thus addressing the issue of optimal utilization of rainfall ...
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At present due to lack of proper utilization and management in non-renewable natural resources, most of the watersheds are in critical conditions. Since about 80 percent of Iran watersheds located in arid and semi-arid climatic conditions, thus addressing the issue of optimal utilization of rainfall is most important. In this research, the surface of micro catchment was isolated by plastic to increase runoff coefficient. Six treatments and three replications were considered in down part of the micro catchment. The surfaceswere prepared by available materials such as greenhouse plastic, gravel, fine and coarse sand, and for infiltration, a filter with 50 cm depth and 15 cm diameter was used. Soil moisture in 30 and 50 cm depths, was monitored by Time Domain Reflectometry (TDR). The first step eas started by cleaning grasses and compacting soil surface and monitoring 18 rainfall events. In the next step, soil surface was covered by plastic and 21 rainfall events were monitored. Results showed that the runoff coefficient increases by six to 47 percent or 7.8 times more than natural condition. The statistical analysis by T-test showed that all treatments and depths of isolated and natural conditions have significantly different results in 90 percent level of confidence. Finally, the average soil moisture content for isolated condition in comparison of natural condition is 6.4 and 9.4 percent in 50 and 30 cm of soil depth, respectively. In other hand, isolated surface increased soil moisture 3.8 and 2.8 times compared to treatments in 50 and 30 cm of soil depth, respectively.
