Ariyan Matboo; Vahedberdi Sheikh; Ali Mohammadian Behbahani; Arash Zare Garizi
Abstract
Introduction
The hills surrounding the international wetlands of Almagol and Ajigol in the Golestan Province are exposed to severe erosion and every year a large amount of sediments from these hillslopes discharge into these wetlands. Whilst a large extent of these surrounding hills, covered with Biological ...
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Introduction
The hills surrounding the international wetlands of Almagol and Ajigol in the Golestan Province are exposed to severe erosion and every year a large amount of sediments from these hillslopes discharge into these wetlands. Whilst a large extent of these surrounding hills, covered with Biological Soil Crusts (BSC), has been destroyed due to lack of awareness of their values, sensitivity and ecological functions. Improving soil properties, preventing direct contact of raindrops with the soil surface, all indicate the important role of BSC in hydrological processes and soil loss control.
Materials and methods
In this study, the role of BSC in the hydrological processes of dry areas was investigated using a rain simulator. After a field survey and evaluation of the area, different treatments including biological crust with a dominant lichen cover, biological crust with a dominant moss cover, an area covered with vascular plants, an area without cover and areas covered with a combination of moss and lichen were selected to perform rain simulation and compare their effects on the hydrological processes of the selected region. Rain simulation was done in 2×1 meter plots for 30 minutes and intensity of 82 mm per hour. The start time of runoff and the volume of produced runoff at the outlet of the plot were measured and recorded. Also, at five-minute intervals from the beginning of the simulation process, 500 ml runoff samples were collected and transferred to the laboratory for testing in order to estimate the sediment concentration and mass. In addition, the depth of the wetting front caused by the infiltration of rain was measured at the beginning, middle and end sections of the plots.
Results and discussion
The results of rainfall-runoff simulations at a 2×1 m2 plot scale with a rainfall intensity of 82 mm.h-1 and a duration of 30 minutes plots, showed that the average mass of sediments from plots with the dominant cover of moss (104 g), lichen (91 g), lichen-moss combination (176 g) and bush (99 g) was significantly higher than bare soil (1133 grams). Therefore, in case of destruction of the existing BSC and the formation of bare lands, the sedimentation rate will increase by more than 5 times. A significant decrease in water infiltration into BSC causes a significant increase of 30-40% in runoff generation compared to the treatment covered with bushes and a significant increase of 8-18% compared to the bare soil treatment.
Conclusions
by reducing soil loss and sediment concentration, BSC cause the production and transfer of high-quality runoff to the wetlands and as a result maintain the ecological function and health of the region’s wetlands. The results of this research show the positive influence of BSC on the hydrological and ecological performance of arid areas in the north of Gorgan Plain and protection of Ramsar-listed wetlands in the region.
Mehdi Bashari; Hamid Reza Moradi; Mir Masuod Kheirkhah; Majid Jafari Khaledi
Abstract
Soils containing rock fragments are covering major parts of land surfaces. Physical and chemical properties of soil are affected by rock fragments as they also affect on the hydrological and erosional processes. So far, many studies have shown the effect of surface rock fragments on soil erosion and ...
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Soils containing rock fragments are covering major parts of land surfaces. Physical and chemical properties of soil are affected by rock fragments as they also affect on the hydrological and erosional processes. So far, many studies have shown the effect of surface rock fragments on soil erosion and runoff. Sediment production is a complex and ambiguous process and a notice to these effects is necessity. Hence this study examines the soil erosion reactions in different impermeable coverage of rocks with erosion plots and rainfall simulator. For this purpose, plots were covered with 0, 5, 10, 15, 20 and 25 percent of rocks, respectively. The results of sediment sampling and measuring the volume of runoff during 30 minutes of rainfall with an intensity of 70 mm/h were analyzed and the results showed that increasing of rock fragment coverage had no effect on runoff volume. But, the amount of sediment increased significantly (p<0/05) in soils containing rock fragments compared to soils without rock fragments. Although, results did not show a linear relationship between sediment values and rock fragment coverage percentage. The highest value of runoff and sediment concentrations observed in soils containing 10 and 20 percent of rock fragment coverage in comparison to other treatments. Finally, by increasing of surface rock fragments to 25 percent, the value of runoff and sediment decreased significantly. The results of this study confirmed the threshold levels in surface rock fragments to increase runoff and sediment values and also their dual roles at different levels.
Mohammad Reza Daneshvar; Mohammad Reza Danaeian
Abstract
In recent years, several flood-spreading projects are constructed in different provinces. Lack of information about planning criteria caused unsuitable ratio between flood spreading area and selected design flood discharge. To find a relation between two above-mentioned parameters this investigation ...
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In recent years, several flood-spreading projects are constructed in different provinces. Lack of information about planning criteria caused unsuitable ratio between flood spreading area and selected design flood discharge. To find a relation between two above-mentioned parameters this investigation was performed in 70-hec area of Miankooh flood spreading station. Soil infiltration tests were carried out before and after every flood spreading event. During the research period six flood events were harvested and several parameters were measured including; discharge, volume of flood, time of flood, volume of tail runoff, time of infiltration, area of flooded sections. In total, 2767288 m3 of flood volume was harvested and 2732361 m3 of water was infiltrated. Considering above-mentioned parameters, relation between maximum input discharge and flooded area, slope of the site, length of the embankment, height of weir and flood time were estimated and the final function was offered. As a result, height of weir and length of embankment have significant coordination (99%) with maximum input discharge.
