Soheyla Aghabeigi; Abdol Rasoul Telvari; Sayed Khalagh Mirnia; Sadat Feiznia; Mehdi Vafakhah
Abstract
Sediment concentration in rivers, especially in seasonal ones, is affected by flood situation due to changes of rainfall or snowmelt events. Due to the importance of flooding flows in inundation and the useful age of reservoirs built on seasonal rivers, the study and assessment of this issue seems to ...
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Sediment concentration in rivers, especially in seasonal ones, is affected by flood situation due to changes of rainfall or snowmelt events. Due to the importance of flooding flows in inundation and the useful age of reservoirs built on seasonal rivers, the study and assessment of this issue seems to be essential. In the present research, suspended sediment concentration variation in spring and autumn floods and runoff from snowmelt in spring, have been studied for Abshine River in Ekbatan Dam Watershed. Over the forecast period, three storms in autumn, two storms in spring and five snow melt events were selected and compared. Analyzing 226 suspended load samples showed its variability in the area. Sediment rating curves in different base times showed different trends. The correlation coefficient (r) were 0.79 and 0.50 for storms and snowmelts and 0.81 for all data, respectively. Also, coefficient and power value analysis of sediment rating curve, presented the same erodibility for hill slope in both seasons (spring and autumn). Separating falling and rising limbs of flow hydrograph and assessing their effect on discharge explains a better Q-sediment concentration relationship. The hysteretic shape of discharge and sediment concentration had clockwise and anticlockwise form and compound pattern of both forms that reflected the distribution of probable sediment sources throughout the catchment.
Ali Reza Masjedi; Abdol Rasoul Telvari; Hasan Kazemi
Abstract
Determination of the erosion depth at the base of the bridge requires knowledge of how to move the river bed sediments. The base of bridge disrupts the normal flow of the river, so turbulence and disturbance resulting in erosion of sediments surrounding the base. The hole created around the base depends ...
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Determination of the erosion depth at the base of the bridge requires knowledge of how to move the river bed sediments. The base of bridge disrupts the normal flow of the river, so turbulence and disturbance resulting in erosion of sediments surrounding the base. The hole created around the base depends on the shape and geometric properties. Moreover, ingredients of river bed and also flow hydraulic conditions such as flood conditions and dune cross can effect on depth of the hole. Since, development of erosion hole hazards the structural stability of the bridge. So predict for amount of hole and necessary measures to suppression are considered as common engineering practices in river engineering. For investigation of basic geometry of the bridge on control scouring around the river bend an experiment in a laboratory flume was done with a 180-degree bend, 2.8 m for central radius, 0.6 m wide and R/B= 4.67 under the walls made of Plax glass. In this study, clear-water scour around the base were studied by putting a basic cylinder with 6 cm diameter, foursquare section, semicircle tip with 6 cm width and 18 cm length in flume at positions 30, 60 and 90 degrees, with rates of 24, 28, 30 and 32 liters per second and a constant depth of 12 cm. For flooring of flume a natural sand by uniform gradation with D50=2 mm and uniformity coefficient of 1.3 were used. The results of this experiment showed that the maximum scour depth during placing the base with cylindrical section and foursquare section with the semicircle tip were alternative during the bend length and in the first half of the bend and at the position of 60 degrees had the maximum scour at the base. Also, scouring in all cases was lower for base with cylindrical section as compared to foursquare section with semicircle tip. In all conditions, increasing of flow have been increased the scour depth.
Haniyeh Asadi; Hamid Reza Moradi; Seyed Hamid Reza Sadeghi; Abdolrasoul Telvari
Abstract
The proper application of instantaneous unit hydrograph theory is very efficient for watershed with lack of rainfall data. Therefore, the present study has been conducted to evaluate the efficiency of Clark instantaneous unit hydrograph modelwith the help of geographical information system in regenerating ...
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The proper application of instantaneous unit hydrograph theory is very efficient for watershed with lack of rainfall data. Therefore, the present study has been conducted to evaluate the efficiency of Clark instantaneous unit hydrograph modelwith the help of geographical information system in regenerating flood unit hydrograph in Kasilian watershed in Mazandaran province. The comparative evaluation is conducted between the 3h-unit hydrographs simulated using Clark model and the one obtained from averaging the observed ones. This comparison is made with the help of statistical criteria viz. relative error, root mean square of error, coefficient of efficiency and bias. It verified high level of compatibility between two unit hydrographs using the Clark model and the hydrograph obtained by averaging the observed data.
Ali Reza Eslami; Abdol Rasoul Telvari
Abstract
The hydrologic events and physical structure of a basin is related to governing climatic conditions. Basins have different hydrologic responses considering their various morphologic and climatic characteristics. It is recommended to separate basins with respect to their major factors into homogenous ...
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The hydrologic events and physical structure of a basin is related to governing climatic conditions. Basins have different hydrologic responses considering their various morphologic and climatic characteristics. It is recommended to separate basins with respect to their major factors into homogenous groups with the same hydrologic conditions. This grouping is effective so that models for estimating flood peak discharge in each homogenous group have higher performance than a single model for all basins. In this research, firstly different morphological characteristic of selected basins were derived using GIS. Based on factor analysis, major variables (factors) including; basin area, weighted-average slope, drainage density and annual mean precipitation were selected. Then, all basins were classified in homogenous groups with respect to major factors using cluster analysis and discriminate functions analysis, statistical methods, and Andrew’s curve as a graphical method. To investigate on the efficiency of grouping, two control basins were selected and their similarity to each homogenous group was carried out using above methods. By applying regression models developed for whole region and homogenous groups, flood peak discharges for two basins with different return periods were estimated. Simulated values compared with observed data and showed that models for homogenous groups have better performance than those for the whole region.
Seyed Hamid Reza Sadeghi; Bahar Salavati; Abdolrasoul Telvari
Volume 2, Issue 2 , July 2010, , Pages 111-115
Abstract
Population ever increasing and consequent demands in recent decade have encouraged farmers to utilize unsuitable and marginal lands such as forests and ranges for agricultural purposes. However, these lands have high soil erosion potential and low productivity and their proper management is therefore ...
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Population ever increasing and consequent demands in recent decade have encouraged farmers to utilize unsuitable and marginal lands such as forests and ranges for agricultural purposes. However, these lands have high soil erosion potential and low productivity and their proper management is therefore a vital task. In the present study, the land use areas have been evaluated in Garan watershed in Kordistan Province, Iran, from 1995 to 2002 by using three digitized images and corresponding changes have been then assessed. The effects of land use changes on changing annual runoff were ultimately evaluated with the help of moving average and hydrological regime analyses. The results of the study revealed that the variation in water discharge thoroughly followed the annual rainfall oscillation which itself affected land allocation to different land uses.
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.
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.
