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Showing 4 results for Peak Discharge
Hossein Malekinezhad, Mohammad Reza Kowsari,
Volume 2, Issue 5 (2-2009)
Abstract
The CN-SCS method is one of the most common methods in runoff and peak discharge estimation. Sensitivity analysis and relative importance assessment of five parameters, CN, time of concentration, rainfall in different return periods, watershed area and has not completely processed by sensitivity analysis. For finding the nature of curve number SCS method in estimating peak discharge and its reaction to change in input parameters, the effects of 5 parameters including CN, time of concentration (TC), watershed area (A), rainfall amount in different return periods (P) and finally, equal to 0.133) were surveyed on peak discharge. Results indicate the effective role of CN on peak discharge as the most important output of model. The sensitivity of the model in estimation of peak discharge highly increases in large return periods. The sensitivity analysis of curve number SCS method was performed in MATLAB programming environment. α were studied in this research. The CN-SCS approachα coefficient (the coefficient for obtaining the time of effective rainfall and it is usually
Maryam Khosravi, Ali Salajegheh, Mohammad Mahdavi, Mohsen Mohseni Saravi,
Volume 4, Issue 12 (10-2010)
Abstract
One of the methods to forecast peak discharge among black box method is artificial neural network. Lack of emphatic regulation to architect network is one of disadvantages in neural networks. There is not a suitable criterion to determine number of layer and number of neuron in hidden layer, type of activation function for hidden and output layers and assay and error method is the only solution. In this research, numbers of suitable neurons in this layer and activation function type in output layer for two sub basin, Gatehdeh and Gelinak, situated in Taleghan basin were investigated by perception neural network with three layers and preservation of type of activation function for hidden layer. 20 percentage data for testing stage, 65 percentage data for training stage and 15 percentage data for validation stage were entered in MATLAB software and sigmoid and linear activation functions with the most application in hydrologic subjects were selected for output layer. Linear function with less RMSE in both stations recognized suitable and the numbers of adequate neurons in Gatehdeh and Gelinak stations were five and six neurons, respectively.
Dr Farshad Soleimani Sardoo, Dr Hamid Noori, , ,
Volume 18, Issue 64 (5-2024)
Abstract
Introduction
In general, the role and importance of watershed operations in improving the condition of pastures, controlling erosion, preventing sedimentation and finally protecting water and soil is not hidden from anyone. The technical and principled implementation of watershed projects causes storage and infiltration of rainfall, increase of vegetation cover, stabilization of erosion and sedimentation, increase of the useful life of dams, adjustment of the slope of waterways and reduction of the speed and power of water destruction. Based on the studies conducted, due to the diversity of ecological conditions, it is not possible to reach a specific pattern or provide specific instructions with the same application in all watershed areas. For this reason, in addition to knowing the area and its issues, it is inevitable to prioritize watershed management operations according to the existing potentials. Examining the results of the conducted research shows that the implementation of watershed operations in watersheds has played an important role in controlling surface runoff. In a study, they evaluated watershed projects on the flood level of the Ramyan area using the HEC-HMS model, and the results showed that the flood has decreased in the period of different returns; In such a way that the greatest decrease in peak discharge and flow volume occurred during the return periods of 10 and 20 years, respectively, and with the increase of the return period, the effect of flood control measures on floods decreases. In this research, in order to evaluate the role of watershed projects in reducing peak flood discharge, HEC-HMS rainfall-runoff model was used, and the amount of discharge was calculated before the implementation of watershed management activities and after the implementation of watershed management activities, and the effect of these projects on the peak flood discharge was determined.
Materials and Methods
Hossein Abad Jiraft watershed is located between 57' 34'' to 57' 43'' east longitude and 28' 19' 13 to 28' 26' 34' north latitude. The area of the watershed is 11258.68 hectares. Also, the weighted average slope of the watershed is 17.83%. More than 60% of the area's land use is pasture, which is the dominant species. In this study, the HEC-HMS model version 3.1.0 was used to simulate rainfall-runoff. Also, the data of 20 climatology stations with a common statistical distance of 30 years (1986-2016) were used.The methodology must be clearly stated and described in sufficient detail or with sufficient references. In order to calculate the amount of losses, the American Soil Conservation Society (SCS) method was used in the HEC-HMS model. The amount of runoff (Q) depends on the rainfall (P) and the water retention volume inside the soil. In all floods, runoff (Q) is always less than or equal to precipitation (P). Similarly, after the occurrence of runoff, the actual amount of water retention (Fa) is less than or equal to the maximum retention capacity (S). As can be seen, CN is the most important parameter to be estimated. CN for average humidity conditions (AMII) is obtained from the relevant table. CN is estimated from the combination of 2 factors of hydrological group and land use at any point of the basin, and CN of the entire basin is calculated from weighted averaging. In this study, to prepare the curve number (CN) map of the region, first, the map of soil hydrological groups in four groups A, B, C and D was prepared by combining the slope map and the map of hydrological units.
Results and Discussion
According to the calculation method described in the previous section, CN was calculated in the sub-basins. The results show that the highest value of CN is estimated in sub-areas H12-1-1-2 with CN: 78.3 and sub-area H11int with CN: 76.9. According to the high value of the curve number in these two sub-areas, flash floods are expected to occur in these two the area is very large and generally the average area curve number is above 70. After completing the input data to the HEC-HMS runoff precipitation model, the model was run for different return periods (RUN) and the calculated peak discharge was extracted. A total of 67472 cubic meters of structures have been built in the entire Hossein Abad basin, including 3 stone and mortar structures with an area of 1139 cubic meters and 10 earthen dams with an area of 66339 cubic meters. The 13 created structures have a total reservoir volume of 222598.1 cubic meters. Due to the effects of watershed management activities, the concentration time of the basin changes and generally increases. This change can be estimated through two factors: the slope of the main waterway and the change in the condition of the cover (CN). The above information was calculated in the modified Kerpich relation of the concentration time and the delay time of each sub-basin of Hossein Abad, after watershed operation. Here, the changes include concentration time, CN and equating some factors with the effective level. By applying the effects corresponding to watershed operations in the runoff precipitation model, the model was run for different return periods (RUN) and the flood peak discharge after watershed operations was calculated.
Conclusion
Today, in order to implement watershed projects, a lot of money is spent in this regard, but perhaps less attention is paid to the effectiveness of these projects. In fact, without monitoring and evaluating these projects, it may not be possible to convince the policy-making managers to allocate credits and the people to voluntarily participate in the implementation and support of watershed projects. Watershed activities are considered as the most important flood risk reduction projects In this research, considering that the implementation of the Hosseinabad-Jiroft watershed project is very costly and is one of the important flood-prone areas of the region, the HEC-HMS rainfall-runoff hydrological model is used to simulate the peak flood discharge before and after the implementation of watershed activities in the Hosseinabad-Jiroft watershed to evaluate the effectiveness of this The projects were used to reduce the peak flow of floods. The results of this research show that watershed management activities in Hosseinabad-Jiroft region play an essential role in reducing the peak flood discharge. This reduction is more than 95% in some sub-areas, which indicates the impact of watershed projects and their effectiveness on the peak flood discharge. Therefore, it can be concluded that the HEC-HMS model is a suitable model for predicting runoff events. Due to the good performance of the HEC-HMS model, this model can be used to estimate floods in basins without statistics with appropriate calibration and obtain acceptable results. The HEC-HMS hydrological model has a good capability in predicting the real time of flood and therefore it was used in this research.
Dr. Ali Reza Nafarzadegan, Dr. Mohamad Kazemi, Dr. Masoud Samiee,
Volume 18, Issue 64 (5-2024)
Abstract
Introduction
Flooding is one of the environmental hazards that causes a lot of repeated damage to water and soil resources in different regions of Iran and around the world. Check dams as a mechanical practice have been built in many watershed areas of the country to control peak discharge and prevent soil erosion. Therefore, it is essential to examine the role of these mechanical practices in flood control at the level of watersheds. The current study aims to investigate the effect of the construction of three proposed structures (two masonry check dams and one embankment dam), with spillway heights of 9, 6, and 8 meters, on flood characteristics in Kander Abdolreza watershed, Fars province, Iran. In other words, this study examines whether the construction of these three consecutive structures fulfills the goal of the operation, which is flood control through a significant reduction in peak discharge and flood volume in the study area. Therefore, the most important variables in this study is the flood volume and the volume of reservoirs proposed for flood control. The amount of flood volume is extracted from the flood hydrograph, and the volume of reservoirs is obtained using a contour map and storage-height curves. It is obvious that if the volume of the reservoir is more than the volume of the flood, all the flood will be attenuated by the structure and the runoff would not pass through the spillway of the dam.
Materials and Methods
In this study, the HEC-HMS model was used to simulate the rainfall-runoff process and the reservoir effect of each of the three proposed consecutive check dams on flood characteristics. The study area, Kander Abdul Reza watershed, is located about 27 kilometers southeast of Lamerd city, Fars province, Iran. According to the division of watersheds in the country, it is part of the Kol-Mehran basin which is a subbasin of the major basin of the Persian Gulf and Oman Sea. In this regard, after preparing the required data, including properties related to topography, rainfall, soil hydrologic group, and designed structures, the peak discharge and volume of flood under different return periods were estimated using the HEC-HMS model. Ghahreman-Abkhezr method was also used to estimate the intensity of rainstorms. The characteristics of the flood in the downstream were investigated in the absence of three proposed structures (two masonry check dams and one embankment dam) and in the next step, the effect of these reservoirs/dams on the hydrograph of the flood was analyzed. Due to the fact that the proposed structures are located upstream of the residential area and the highway, the basis of the design of the structures was the flood discharge with a return period of 100 years. Finally, using the obtained results, the percentage of reduction in the peak discharge of the flood under the influence of the construction of each of the reservoirs/dams was determined and compared.
Results and Discussion
The outcomes of SCS unit hydrograph for Kander Abdolreza watershed showed that the flood peak discharge in the return period of 2, 5, 10, 25, 50, and 100 years is equal to 7, 32, 46, 72, 91, and 116 m3.s-1, respectively; so that the time base of the hydrograph varies from 6.5 hours in the 2-year return period to nearly 9 hours in the 100-year return period. Meanwhile, the volume of runoff varies from 1.73 m3 in the return period of 2 years to 1053 m3 in the return period of 100 years. The results also showed that if the three proposed three consecutive structures were built, with a total reservoir volume of 614367 m3, the peak flood discharge would fall from 116 m3.s-1 to 32 m3.s-1 over a 100-year return period. In addition, the outcomes of the simulation of the rainfall-runoff process in the study watershed indicated that the reduction in the peak discharge and volume of the flood after the implementation of the proposed structural measures for the 50-year return period was 84% and 73%, respectively; and for the 100-year return period it was reduced by 72% and 57%, respectively. Thus, according to the results of the simulation of the effect of the designed structures, it can be claimed that the proposed structures for the study watershed would have the ability to mitigate and control floods.
Conclusion
The implementation of the proposed structural measures for the Kander Abdolreza watershed, including two masonry check dams and one embankment dam, in addition to reducing the peak discharge and the volume of flood flows, can stabilize the longitudinal profile of the stream channels, which is useful for the conservation of soil and water resources in the study area. At different return periods (2, 5, 10, 25, 50, and 100 years), the three proposed structures have the required capacity to store runoff and reduce the peak discharge in the study watershed; however, as the return period increases, the role of these reservoirs/dams in controlling the flood and reducing the peak flow decreases. Moreover, the effect of the proposed consecutive structures system on peak flow reduction is greater than the effect of these structures on flood volume reduction.
In general, to increase the effectiveness of the watershed studies plans, it is recomended to include the study of the impact of the implementation of structural measures on the characteristics of flood flows in the service description worksheet of these projects so that the decision to carry out or not to carry out for structural operations in each basin or sub-basin is made based on the simulation results and with more detailed information. In addition, to better evaluate the proposed structural measures for flood control, it is suggested to prioritize the installation of hydrometric stations in ungauged watersheds that are prone to flood generation.
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