Banafshe Yasrebi; Majid Soufi; Mir Khalagh Mirnia; Jahangard Mohammadi
Abstract
This research focused on studying the morphometric characteristics, topographic threshold of gullies and their relationships, dominant process of gully initiation and development stages as well, in agricultural and rangeland land uses. Also, morphometric characteristics of 120 gullies including top width, ...
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This research focused on studying the morphometric characteristics, topographic threshold of gullies and their relationships, dominant process of gully initiation and development stages as well, in agricultural and rangeland land uses. Also, morphometric characteristics of 120 gullies including top width, bottom width and headcut height and surface characteristics of gullies contributing area including vegetation, rock fragment and bare soil by 1 m2 plot and soil samples from top soil and gullies wall were collected in semi-arid part of Ilam Province. Results showed that top width–depth ratio of gullies in cropland and rangeland is 2.1 and 1.5, respectively that widening and deepening has more important role in gully growth. Top width-length ratios are 0.41 and 0.57 in croplands and rangelands, respectively that shows rangeland gullies are more elongated. Negative exponential relationship between those ratios and slope shows the effect of topographic factors especially slope on final shape of gullies. Bottom width-top width ratio in croplands and rangelands is about 0.33 and 0.3, respectively and cross section shapes are trapezoidal and V shape. Results showed that slope describes 16 percent of cross sections area variation and lateral growth of gullies in croplands and rangelands and describes 84 and 73 percent of gully volume variation. Effective factors on gully volume are sand content in top soil, land use and slope. Studied gullies in both land uses have mean fractal dimension of 1.08 and has linear growth with length and power growth with volume of gully. Power of Hack law in studied gullies in croplands and rangelands gullies are 0.5 and 0.54, respectively.
Nader Jalali; Fazel Iranmanesh; Mohammadhadi Davoodi
Abstract
Generally, satellite images and climatological and environmental data are used simultaneously in dust storm studies. Most of the processing techniques are limited to a few indices such as brightness temperature differences, normalized dust density index, aerosol optical depth, false color composite and ...
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Generally, satellite images and climatological and environmental data are used simultaneously in dust storm studies. Most of the processing techniques are limited to a few indices such as brightness temperature differences, normalized dust density index, aerosol optical depth, false color composite and visual image interpretation. Since the reliability of the above-mentioned methods are varied, so an attempt was made to increase the reliability of automatic spatial image clustering by contributing the expert knowledge via visual image interpretation. Therefore, the required satellite images were collected for a period of 2005 to 2008, in Mesopotamian, Syria and south-western provinces of Iran. For doing this, the MODIS color composite images were decomposed into their ordinary bands and then used for further analysis. In this research, spatial image clustering followed by visual image interpretation (hybrid classification) was applied for accurate mapping of geographical extents of dust storm with different intensities. The sources of dust storms were also identified through visual image interpretation by considering the interpretation criteria such as shapes and patterns. Comparison of the previous results and obtained by this research, indicated critical conditions in terms of dust storm occurrence in the region. Image clustering and hybrid classification led to daily dust persistence over the region and then those images compiled in order to prepare annual total heavy dust persistence map. The result of using brightness temperature difference method verified similarity and reliability of obtained results. Therefore, this simple method could be proposed for identification of dust sources, related plumes and their affecting areas, when raw image data are not available.
Hamid Reza Peyrowan; Mohsen Shariat Jafari
Abstract
One of the most important problems that empirical model users in Iran are facing with, is that these models are prepared for countries with special conditions such as lithology factor, which scores are given based on geology condition of origin country that are not compatible for a vast country like ...
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One of the most important problems that empirical model users in Iran are facing with, is that these models are prepared for countries with special conditions such as lithology factor, which scores are given based on geology condition of origin country that are not compatible for a vast country like Iran with a great lithological variation. This research was conducted to reduce such problems and increase the efficiency and localization of these kind of models and provides rock erosion sensitivity factor for their special conditions. In PSIAC and EPM as a common experimental models, lithology factor is an important agent among other effective factors. In this research, a comprehensive classification of erodibility has been produced in 10 orders, based on mineralogy, chemistry, texture, structure and mechanical properties. Regarding to aridity of many parts of the country, and low rate of soil generation, erodibility rates of geological formations would be an important tasks. Results showed that, about 70 percent of the area covered with very low to low strength lithology to erosion and have a high potential of sediment yielding. Geological formations’ erodibility has been classified in30 Tamab watershed with order of 4 and the results are compared with EPM results and monitored values in river gauging stations. Results also indicated a good agreement with high confidence with natural conditions and with respect to other important factors of the watersheds such as topography and rainfall.
Bahram Saghafian; Saman Mohammadi; Baghe Ghermezchshme
Volume 1, Issue 1 , May 2009, , Pages 32-45
Abstract
Calculating low flow characteristics is very important for planning of water diversions; providing water for hydropower, water quality threshold in streams, water supply for cities and industries and estimate of sewerage discharge threshold. The objective of this research is analyzing low flow with different ...
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Calculating low flow characteristics is very important for planning of water diversions; providing water for hydropower, water quality threshold in streams, water supply for cities and industries and estimate of sewerage discharge threshold. The objective of this research is analyzing low flow with different duration and return periods and extracting low flow regional models for locations without hydrometric station. This research was carried out in Gilan province where 35 hydrometric stations with long-term and reliable daily discharge data were selected. Low flows of durations 10, 30, 60, 90 and 180 days were estimated. Using frequency analysis, several statistical distributions were examined and log Parson Type 3 was found the best distribution for flow duration over 60 days and log normal best fitted flow durations shorter than 60 days. Then low flows of different return periods including 2, 5, 10, 25, 50, 100 and 200 year were calculated. Independent factors were identified using factor analysis that included basin area, mean annual rainfall, slope, average elevation, and drainage density. Cluster analysis divided the basins in two homogeneous regions. In each homogeneous region, multivariate regression through step-by-step method determined basin area, mean annual rainfall and slope as independent influential parameters in low flow regional models. Regional models were extracted for low flow with various durations and return periods.
