Bagher Heidarpour; Bahram Saghafian; Abolfazl Shamsai; Saeed Golian
Abstract
In present research, the exceptional floods of study area at Golestan Dam watershed were identified using one of the standard tests of identifying outlier values, e.g. Dixon, Grubbs and Grubbs and Beck.In order to determine the probability distribution function and the effect of direct application of ...
Read More
In present research, the exceptional floods of study area at Golestan Dam watershed were identified using one of the standard tests of identifying outlier values, e.g. Dixon, Grubbs and Grubbs and Beck.In order to determine the probability distribution function and the effect of direct application of the floods in flood frequency analysis, two sets of analysis were performed one with the whole data series and the other with deleting the outliers. At this stage, 15 different probability distribution functions were applied with biased and unbiased estimates of the parameters using three estimation methods namely method of moments, maximum likelihood and Probability Weighted Moments methods. According to Kolmogorov-Smirnov and Chi-square goodness-of-fit tests and index error calculation, the log Pearson Type III distribution was determined as the best distribution for both complete data series and data without exceptional floods. Results of the Flood frequency analysis at this stage showed that the probability distribution did not change after removing the exceptional floods, but was highly influential in the magnitude of design flood.In the next step, the method of Water Resources Committee of the United States was used to combine the exceptional floods with other observational data. Using the sensitivity analysis, the historical period for exceptional floods at Tangrah, Tamer and Galikesh stations were calculated to be 300, 60 and 80 years, respectively. The derived historical period were considered in calculation of the flood values for different return periods. For example, 1000-year design flood for the complete data series were calculated to be 14946, 1639 and 2635 cms for the aformentioned stations respectively and reduced to 1434, 1423 and 1296 for the complete data series with modification of the parameters for the probability distribution functions. Therefore, the technique used in this study effectively reduced the cost of the designed hydraulic structures.
Peyman Daneshkar Arasteh; Masoud Tajrishy; Bahram Saghafian
Abstract
Earth skin temperature including soil, water, snow, and vegetation surface temperatureis one of the main variables in geo-science studies. Generally, spatial distribution ofsurface temperature is needed in such studies. Spatial monitoring of surface temperatureis possible using remote sensing data, and ...
Read More
Earth skin temperature including soil, water, snow, and vegetation surface temperatureis one of the main variables in geo-science studies. Generally, spatial distribution ofsurface temperature is needed in such studies. Spatial monitoring of surface temperatureis possible using remote sensing data, and the time series of images provide acontinuous spatio-temporal framework required in modeling energy balance of regionalevaporation, optimization of energy demands or dispersion of atmospheric pollutions. Inthis paper, some common methods of surface temperature estimation using satelliteimagery were introduced and calibrations of several forms of split window equationwere addressed for Sistan area, Iran. Split window method is based on the fact that theatmospheric transmittance varies with wave length and uses a combination of thermalinfra-red brightness temperature and emissivity. To calibrate the split window equation,ground observations and 22 NOAA/AVHRR images during 1992 to 2002 were used todevelop regression models. Statistical tests were performed to evaluate the equationsand coefficients. Ten AVHRR images were used to verify the developed equations. Theresults indicated that three different forms of split window equations successfullypassed the χ2 statistical test. Both, F and Kruskal-Wallis tests showed that they are notstatistically different at 95 percent significant level. Therefore, the simplest form ofequation was used to derive surface temperature maps in the Sistan region, and isrecommended as the most applicable one.
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, ...
Read More
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.
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 ...
Read More
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.
