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 ...
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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.
Saeed Golian; Ahmad Ahmadi; Narjes Salarian
Abstract
A check dam is a small dam with a simple and low cost structure and because of its specific material and simple building technology, it has a wide range of applications in flood control projects. In this research, the effects of check dams on reducing the flood peak and increasing the time of flood flow ...
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A check dam is a small dam with a simple and low cost structure and because of its specific material and simple building technology, it has a wide range of applications in flood control projects. In this research, the effects of check dams on reducing the flood peak and increasing the time of flood flow to reach to peak were investigated for Kan basin in north-west of Tehran.The hydraulic and hydrologic situation of the Kan basin was modeled using HEC-HMS software. Using hydrologic modeling the effect of building check dams on flood characteristics was studied in three scenarios of river slope change. The results showed that check dams reduced the flood peak to reduce between 0 and 0.9% in the first scenario (0.5 of the natural slope) and from 0.4% to 3.5% and 3.9% to 10.6% in the second (0.1 of the natural slope) and third (0.01 of the natural slope) scenarios, respectively. The time to peak also increased from 10 to 50 minutes. In hydraulic-hydrologic modeling, the effect of constructing check dams with no sediment in their reservoir was investigated for rainfalls of different return periods. The results revealed that with increase in rainfall return period, the effect of check dams on reducing flood characteristics will decrease. For instance, in the case of 100 check dams, the percentage reduction in peak outflow will decrease from 22.8 to 1.2 % for rainfalls of 2 and 20 years return period, respectively. In general, construction of check dams has no considerable influence on reducing constructive effects of floods. In other words, check dams should be used together with other structural and non-structural flood control methods.
