Bahram Saghafian; Bagher Ghermezcheshmeh; Masoud Samiei; Reza Asheghi
Volume 1, Issue 3 , October 2009, Pages 140-152
Abstract
Study of effective factors on sediment load of river basins has attracted more attention in watershed management. In spite of the short record length, sediment load measured in stations can be used in such studies. In this study, 20 sub-basins with measured sediment data was identified and some 48 physiographic, ...
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Study of effective factors on sediment load of river basins has attracted more attention in watershed management. In spite of the short record length, sediment load measured in stations can be used in such studies. In this study, 20 sub-basins with measured sediment data was identified and some 48 physiographic, climatic, geologic, and vegetation index factors were extracted for the sub-basins using GIS. Surface curvature and satellite image-based vegetation indices were considered for the first time. Based on factor analysis, four factors namely total area, percent of convex area, percent area with northwest aspect and percent area with NDVI>0.4 were the main factors. Cluster analysis was applied to delineate homogeneous regions, which led to two regions. The results indicated that the factors mentioned above are the most influential factors on sediment load.
Sattar Chavoshi; Mohammad Reza Yazdani; Abdorasoul Telvari
Volume 1, Issue 3 , October 2009, Pages 153-159
Abstract
Flood risk estimation is one of the most important subjects for Hydrologists. The main objective of flood risk estimation is study on past events in order to determine the following flood risk. There are various methods for flood risk estimation. Rainfall- runoff and empirical equations are the most ...
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Flood risk estimation is one of the most important subjects for Hydrologists. The main objective of flood risk estimation is study on past events in order to determine the following flood risk. There are various methods for flood risk estimation. Rainfall- runoff and empirical equations are the most recently used methods. In these methods, rainfall is the main parameter influencing flood mechanism. In this research, spatial distribution of rainfall pattern in Esfahan province is studied. Esfahan province with 10.5 million ha area is located in central part of Iran with different topography, climate and ecological condition. A number of 203 rainguages, located in the study area and nearby, were studied. Recorded data of 32 years, from 1968-2000 and a total number of 1654 storm events with less than 1 hour to 72 hours duration were investigated and three index events, i.e. widespread and maximum events, were used. The common methods of geostatistics like kriging, Co-kriging, IDW and TPSS were applied to interpolate the recorded points to non-observed ones. Results showed a low correlation between rainfall and elevation in the study area. Among the studied interpolation methods, kriging showed the best results, from which the Gussian and Spherical models best fitted to the observed points. In order to gain best results, it is recommended to add the number of rainfall gauge sites according to the World Meteorological Organization (WMO) standards. Also, grouping the study area into homogeneous regions and studying DAD in each homogeneous region is advised.
Ghasem Habibi Bibalani; Shahriar Sobhe Zahedi; Zia Bazhrang
Volume 1, Issue 3 , October 2009, Pages 160-166
Abstract
A traction effect by lateral roots is one way in which roots contribute to lateral in-plane reinforcement of a shallow soil mass. In contrast to the effect of vertically-extending roots, whereby soil is reinforced by an increase in its shear strength, the traction effect reinforces the soil by enhancing ...
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A traction effect by lateral roots is one way in which roots contribute to lateral in-plane reinforcement of a shallow soil mass. In contrast to the effect of vertically-extending roots, whereby soil is reinforced by an increase in its shear strength, the traction effect reinforces the soil by enhancing the tensile strength of the rooted soil zone. To verify whether or not a traction effect exists in the root system of Mamraz vegetation، north of Iran, and to investigate the magnitude of this effect, a direct in situ test was conducted at a site in the Shanjan rangelands. The results from the site showed that, in the topmost soil (0-20cm), the lateral roots are able to provide a tractive force of up to 167.4 N (Newtons) over a vertical cross-section area of 20-50 cm2, or an increase in the pulling resistance of the rooted soil by 24.5%. The test results imply that, together with the Mamraz vertical roots, which anchor the shallow rooted soil zone to the deep and more stable soil mass, the lateral roots of the Mamraz, through their traction effect, are able to mitigate against shallow instability in the rangelands slopes, such as shallow slide and creep, to a certain degree.
Mohammad Reza Yazdani; Sattar Chavoshi; Morteza Khodagholi; Bahram Saghafian
Volume 1, Issue 3 , October 2009, Pages 167-178
Abstract
Most parts of the Isfahan province are located in central arid land of Iran and are sensitive to drought occurrences. So it is required to study drought for prediction. There are many ways to define drought using different indicators. Climatology drought was evaluated using annual precipitation time ...
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Most parts of the Isfahan province are located in central arid land of Iran and are sensitive to drought occurrences. So it is required to study drought for prediction. There are many ways to define drought using different indicators. Climatology drought was evaluated using annual precipitation time series and different truncation levels including 30% 40, 50, 60, 70, 80, 90 and 95%. In this study 85 precipitation stations were selected in Isfahan province and around of it, in period of 1966-1998.Interpolation methods such as, kriging, Co-kriging, inverse distance weighted and TPSS were evaluated for interpolation of truncation levels and the error of each method was calculated. In the selected methods, Co-kriging method had minimum error and TPSS method had maximum error. Drought extension maps were drawn for each truncation levels using ILWIS software. Also water volume of probable precipitation is calculated for each truncation levels. Results showed about half of rainfall events occurred in 30 percent truncation level, whereas about 80 percent of the events are in 30 percent truncation level. Thus intense droughts occurred in the study area. Maximum frequency of drought occurrences in basis of truncation levels in study area are 30, 80, 60, 50, 40, 90, 70, 95%, respectively. Results indicated that truncation levels are suitable method for climatological drought evaluation in the studied area.
Manouchehr Amiri; Hadi Nazari pouya; Hamid Reza Peyrovan
Volume 1, Issue 3 , October 2009, Pages 179-188
Abstract
The marl soil types are very sensitive to erosion and are deposited into reservoirs of dams and areas of flood spreading in form of considerable sediment annually. This process increases the expenses of filtration of drinkable water and pre-filtration of water of artificial recharge severely. So the ...
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The marl soil types are very sensitive to erosion and are deposited into reservoirs of dams and areas of flood spreading in form of considerable sediment annually. This process increases the expenses of filtration of drinkable water and pre-filtration of water of artificial recharge severely. So the investigation of marl soil types from different aspects is very important for experts and researchers. In this research, it was tried to recognize the effective variables on erosion rate of marls in Hamedan province. 49 samples of 41 spots in 3 marl areas were taken to determine the physical and chemical properties. The characteristics of place of sampling like; slope, geographical situation and privilege of 7 parameters for surface factor of soil were noted. Also, the test of simulated rain was done by the Kamphorst΄s rainfall simulator apparatus in the 41 above spots and 41 samples of runoff were taken and the amount of soil lost were measured and calculated by simple method in the laboratory. The amounts of 23 physical and 15 chemical variables were determined. Then, all data were evaluated by Kolmogorov-Smirnov test and the abnormal data were normalized by logarithm and were evaluated by correlation, bi-variate and multivariate regression tests. The results showed that only 9 variables have significant and linear relation with soil loss, where plastic index, clay percent and clay ratio are the most important variables for evaluation of marl soil loss at marls of investigated areas respectively.
Ramin Bidel; Abdoralsoul Telvari; Masoud Goodarzi
Volume 1, Issue 3 , October 2009, Pages 189-200
Abstract
Rainfall is one of the main variables to be studied in climatologic studies. Also it is an important variable because of its distribution status both temporally and spatially. In other word, it varies with synoptic patterns. Therefore, river structure designing based on non-native design storm ...
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Rainfall is one of the main variables to be studied in climatologic studies. Also it is an important variable because of its distribution status both temporally and spatially. In other word, it varies with synoptic patterns. Therefore, river structure designing based on non-native design storm suffer from high risk. For more safety, we need to recognize precipitation condition of study area and its temporal patterns. In this study, rainstorms of seven stations in Kermanshah province are studied and after derivation of 2989 storm events, temporal distribution patterns of rainfall by Pilgrim (graphical mean) and Huff (probability) methods were calculated. The examination of rainstorms in all of the stations specified that rainstorms of 1 hour group contain 30 percent and 1 to 6 hour groups more than 80 percent of whole rainstorms as well. Furthermore, the inspection of resulted patterns and distribution quantity in each time quarter showed that 48.21 percent and 7.14 percent of rainstorms in all of the stations and whole groups has reposed in second and fourth quartile respectively. This study shows that 80.35 percent of rainstorms belong to second and third quartile. In regional patterns, 1 to 24 hour groups, second and third quartile contain 75 percent and 25 percent of total rainstorms respectively. According to Huff or probability distribution method, most of the station in short time rainstorms (1 to 6 hour) are second quartile and remaining groups are third quartile. Regional types in this method have similar condition in most groups and are confirmed by median types. Results of comparing these patterns show no correspondence with S.C.S patterns, but IA pattern corresponds with Kernd station. Probability and median have good correlation in the second quartile relatively.
Ali Reza Masjedi; Manouchehr Fathi Moghadam
Volume 1, Issue 3 , October 2009, Pages 201-2011
Abstract
The existence of vegetation cover in a region can reduce the velocity of surface run-off and prevent soil erosion. This can substantially control the occurrence of destructive floods in the region. One reliable method used in protecting flood-forming catchments is the biological method. Also, one factor ...
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The existence of vegetation cover in a region can reduce the velocity of surface run-off and prevent soil erosion. This can substantially control the occurrence of destructive floods in the region. One reliable method used in protecting flood-forming catchments is the biological method. Also, one factor that represents the hydraulic resistance in plants is roughness coefficient. Measuring the coefficient and its impact on the flow velocity and shear stress reduction in the plants is of outmost importance. One of the known species used extensively in soil stabilization and protection is Tamarix sricta .This species resists against various climates and is easy to be planted. With its needle leaves and rough external organs, Tamarix sricta reduces the flow velocity and prevents further soil erosion. In this research roughness coefficient of the Tamarix sricta was investigated. The plant studied in non-submerged and sub critical condition flow using a flume with the length of 12.6 m, width of 0.5 m and height of 0.6 m in different velocity, discharge and depths. The height of plants in this is 35 cm with a natural arrangement in trays of 2.8 m in length laid over the bed of the flume. The total number of the experiments is 22.The results of this study show that roughness coefficient of plants is function of velocity, depth, hydraulic radius and plant types. Because of its high roughness, this species is an appropriate alternative to be used in reducing the flow velocity and protecting the soil from any erosion possibility.
