sima rahimi bondarabadi; Bahram Saghafian; Tayeb Raziei
Abstract
Introduction
Monitoring of hydrological droughts is one of the basic needs of water resources management in watersheds, especially in the field of water agriculture. Drought is divided into three major groups: meteorology, agriculture and hydrology. Hydrologic drought can be studied in different ways. ...
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Introduction
Monitoring of hydrological droughts is one of the basic needs of water resources management in watersheds, especially in the field of water agriculture. Drought is divided into three major groups: meteorology, agriculture and hydrology. Hydrologic drought can be studied in different ways. One of the common methods is the use of low flow indexes and threshold level approach.
Materials and methods
In this research, the minimum flow indices (Q75, Q90 and Q95) extracted from the flow continuity curve and minimum flow series (10 and 30 days) as well as the amount of flow deficit for hydrological drought monitoring in the Caspian Sea Basin were investigated and evaluated. For this purpose, 40 hydrometric stations with 41-year statistics (1970-2011) were selected. In the next step, the data of the studied stations were evaluated in terms of homogeneity, independence and randomness. Then, with the help of hierarchical cluster analysis and step-by-step regression, hydrological homogenous areas were determined and regional analysis of these indicators was done.
Results and discussion
In order to investigate the characteristics of the minimum current in the Caspian Sea Basin, first, the continuous flow curve was drawn for each of the stations, and then, three indices Q75, Q90 and Q95 were calculated for each of the stations. For the spatial comparison of the minimum flow, the specific minimum discharge or qs (minimum discharge value divided by the area) was used. qs75 index varies between 0.0006 and 13 m3s-1per km2. The value of qs75 is less (drier) in the eastern parts and in the western parts of the region, the amount of dryness of the stream is less than other places. Examining the spatial distribution maps of these three indicators shows that the trend of their spatial changes is almost similar and they all indicate that the western regions of the Caspian Sea Basin are more humid than the eastern and central regions. In the next step, to examine the minimum flow indicators, a series of minimum flows of 10 and 30 days was prepared. By comparing distribution parameters with the help of scoring method, Log-Pearson type 3 distribution was selected as the best distribution in most stations. After choosing the most appropriate distribution, the values of the 10-day and 30-day minimum indices with different return periods were calculated. Examining the average indicators shows that the minimum discharge value of 10 days with a value equal to 0.01 m3s-1 in Vatana Station (12-035) located in the east of the basin and the highest with a value of 19.2 m3s-1, it is at Rudbar Station (17-034) in the western region of the basin. Regarding the average minimum discharge of 30 days, the lowest value is equal to 0.20 m3s-1 and the highest value is equal to 8.52 m3s-1in these two stations. In order to investigate the temporal changes of hydrological drought intensity, the annual time series of 10-day and 30-day low flow at each station were plotted in relation to the year of their occurrence, in order to determine the trend of changes in the drought situation in different years. Examining the time trend of the minimum flow indicators on the graphs, shows a decrease in the value of the indicators in recent years and a negative trend of the indicators. In other words, the graphs in almost all stations show hydrological droughts (reduction of minimum flow indicators) during recent years. In order to determine the length of minimum flow periods, 10 and 30 day moving averages of discharge were compared with Q90 index value in different stations. The results show that the persistence of drought in the central parts of the Caspian Sea Basin (Pulor, Razan, Karsang, Tange Lavij, Pol Zoghal and Zowat sub-basins) is more than the rest of the regions, these sub-basins are located in Mazandaran Province. The lowest duration of drought (between 22 and 25 days) is related to the sub-basins of Shalman, Pol-e-Sazman, Pashaki, Astana and Tutkabon in the eastern part of the Caspian Sea Basin and in Gilan Province. The eastern parts of the basin have also experienced a drought period between 28 and 30 days.
Conclusion
Results indicate that the years 1990 to 2010 have undergone severe and long droughts in most of the stations. The review of the spatial distribution of indexes shows better conditions in the western parts of the study area compared to the eastern sections in terms of dryness. However, the duration of hydrological droughts in the central study area is longer than in other parts of the basin. Investigating the time trend of the indexes also shows the increase in the frequency and duration of hydrological droughts in recent years. A comparison of different indexes shows that all of them have similar results in the region. The results of cluster analysis divided the area into three distinct homogenous units (in 0.01 significant level). The result of the regional analysis showed that in the eastern homogeneous region, the influencing factor on low flow indexes is elevation, while in the central and western regions, the drainage area and density have a greater impact.
Rahim Kazemi; Jahangir Porhemmat; Forood Sharifi
Abstract
The Flow Duration Curve (FDC) is a classical method used to graphically represent the relationship between the frequency and magnitude of stream flow and is required as a prerequisite for water resources management projects. In this study, by analyzing daily data of hydrodynamic stations, 47 stations ...
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The Flow Duration Curve (FDC) is a classical method used to graphically represent the relationship between the frequency and magnitude of stream flow and is required as a prerequisite for water resources management projects. In this study, by analyzing daily data of hydrodynamic stations, 47 stations with the appropriate statistics and the common period between 1976 and 2011 was selected in a semi-arid region of the country. Using a topographic map with a scale of 1: 50000 and determining the position of the stations, the study area was determined and 11 physiographic parameters influencing the flow duration curve including: average height, basin area, gravilillus coefficient, basin slope, main river length and hydrological parameters including annual rainfall, Base flow index, hydrograph recession constant, curve number, permeability and the number of rainy days were extracted for each basin. The flow duration curve indices were then extracted using daily flow data. Then factor analysis was performed and independent factors influencing the flow duration curve were determined. Finally, homogeneity was performed based on independent main factors and the regression relations of the curve indices were extracted in each homogeneous region.In order to investigate the validity and accuracy of the models in homogeneous regions, error-independent test methods, normal distribution of errors and control stations were used. The results showed that the selected factors for factor analysis in semi-arid climatic zone (75.875 percent) of the variance of data were explained. The six parameters of precipitation, curve number, slope, rainy days, permeability and area were known as the most effective parameters. The results of the accuracy assessment of the models using the control stations showed that the relative error of the relations presented in the homogeneous region was 0.17, 2.17, 2.73, 1.53 and 1.94, respectively. The normal distribution of errors, the coefficient of determination of more than 0.90 and the Durbin Watson coefficient between 1.5 to 2.5 also Nash-Sutcliff near "one" indicate the reliability of the regression relations presented for estimating the flow duration curve indices in the ungagged catchments in semi-arid areas of the country.
Rahim Kazemi; Jahangir Porhemmat
Abstract
Estimating the runoff coefficient that is influenced by morphometric, geologic and hydro-climatologically factors are the most important issues in hydrology and information of its role in the planning and management of water resources is more important. Clustering catchments is the best method for the ...
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Estimating the runoff coefficient that is influenced by morphometric, geologic and hydro-climatologically factors are the most important issues in hydrology and information of its role in the planning and management of water resources is more important. Clustering catchments is the best method for the analysis of hydrological parameters in the absence of full coverage of hydrological data. In this research, twenty two hydrometric stations with common period from 1974 to 1999 were selected. Physiographic parameters of the catchments were extracted. Runoff coefficient was calculated and then base flow was extracted from using one parameter recursive digital filters. Lithological units using digital geological map, with the scale of 1: 250,000, based on expert opinion divided on two classes and area covered by each unit in each catchment were calculated. Factor analysis using 15 parameters were conducted. Catchments using independent factors in different hierarchy methods includes: nearest neighbor, furthest neighbor, median clustering, centroid clustering and Ward method were classified. Then, the regional equations using linear regression at 1% significant level were determined. To compare and evaluate the accuracy and efficiency of the models, independence errors, colinerity and normal distribution of error were tested. The results of factor analysis showed that all variables are to be classified in terms of five factors which 85.9% of the variance was included. Results of homogeneity showed that the basins in homogeneous methods of nearest neighbor, furthest neighbor, centroid clustering and median clustering, were all the same and classified in two groups with the similar components. The results of accuracy assessment showed that the accuracy of nearest neighbor methods was more accurate, and because of low relative error (25.4%) and MAE of 7.85 and RMSE of 9.62 was diagnosed as the best method for regional analyzing of runoff coefficient in the study area.
Saeed Jahanbakhsh; Behrouz Sari Sarraf; Abdolmohammad Ghafouri Roozbahani; Sima Rahimi Bandarabadi
Abstract
Hydrologic drought can be studied in different ways. One of the common methods is the use of low flow indexes. In this study for the purpose of determine of the identity of aspects of low flow, the homogenous zones, the extraction of regional regression models, and finally, the study of low flow trends ...
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Hydrologic drought can be studied in different ways. One of the common methods is the use of low flow indexes. In this study for the purpose of determine of the identity of aspects of low flow, the homogenous zones, the extraction of regional regression models, and finally, the study of low flow trends of Karkheh river basin, applied the data of 13 hydrometric stations during the statistical period of 1960-2000. After qualitative and quantitative controlling and the retrieval of missing data used flow duration curves for indexes such as Q75, Q90 and Q95. Also frequency analysis of 10-day, and 20-day low flows was carried out for indexes such as Q10,5, Q10,50, Q10,100, Q30,5, Q30,50, Q30,100 and some more indexes. Afterwards, some other factors like physiographic, climatic, geologic and vegetation cover were applied as influential parameters in the regional analysis. These factors were used in cluster analysis and stepwise regression estimations. Final step was the trend analysis of times series of the indexes. Results indicate that among the indexes being calculated, Q10,100 and Q95 had the minimum quantities, whose amounts reduced as the return periods increased. On the hand, the time spans of 1998-1999, 1999-2000, 2000-2001 have undergone severe and long droughts in most of the stations. The review of the spatial distribution of indexes show better conditions of the south-eastern parts of the study area compared to the northern and southern sections in terms of dryness. Results of cluster analysis divided the area into two distinct homogenous units (in 0.01 significant level). In the area No. 1, the elevation factor, in the area No. 2, the drainage density, and in general, the factors such as the mean of area and drainage density have the highest effects. The Spearman statistic, and Mann-Kendall findings also indicate that the low flow in upper basin have negative trend during the statistical period.
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.
