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Showing 21 results for Frequency

S. Chavoshi, S.s. Eslamian,
Volume 3, Issue 3 (10-1999)
Abstract

Designers of hydraulic structures are often faced with the problem of estimating flood frequencies at stream sites, where little or no flow information is available. A regional regression model is widely used which relates physical and climatological parameters to flow characteristics. In this study, a new method is used which is based on the station-year technique and combined records for several stream-flow gaging stations to make a single composite sample. This method, named ‘hybrid’, was proposed by Hjalmarson and Thomas (1992). It was applied to a group of records from 17 apparently homogeneous stream gaging stations to determine regional flood frequency equations. The study area consists of two adjacent basins, Gavkhoony and North Karoon in the central part of Iran. Using area and mean elevation of the catchments as the most important criteria in relation to peak discharge, the interactive process of the hybrid method was performed, resulting in two-parameter models of regional flood frequency. The performance of the hybrid method was evaluated by comparison with the regional relations determined from a multivariate regression. The comparison revealed that the accuracy of the hybrid method was significantly better than the regression method for low return periods.
S.s. Eslamian, V. Salimi, S. Chavoshi,
Volume 4, Issue 2 (7-2000)
Abstract

Peak discharge is one of the basic parameters in the design of hydraulic structures. There are various methods for peak discharge determination. Regional flood frequency analysis is based on physical, climatological and hydrological characteristics of basins. The objective of this study is to examine different models for the estimation of quantiles for some catchments in western Iran (namely: Gharehsoo, Gamasiab, Kashkan, Seimareh, Sezar and Abshineh) for which only maximum daily mean discharge data exist. In this research, peak and maximum daily mean discharges for 11 stream gauging stations were collected for a 21-year period. The ratio of these two discharges (R) and mean and standard deviations of peak discharges and maximum daily mean discharges were computed. Catchment characteristics including catchment area, catchment perimeter, main channel length, mean elevation, mean slope equivalent rectangle length, circular ratio, Gravelius coefficient, drainage density, time of concentration, relief ratio and diameter of the circle having equal area with the catchment were computed. Linear regression analysis was performed between independent variables of the catchments and mean standard deviation of the parameter “R” to develop a relation. The results of this study can be applied to the estimation of extreme flow values for non-recording stream gauging stations (daily reading sites).
M.a. Izadbakhsh, S.s. Eslamian, S.f. Mosavi,
Volume 5, Issue 2 (7-2001)
Abstract

Flood is one of the catastrophic events that has attracted the hydrologists’ attention. In this research one of the important flood indices, i.e. maximum-daily mean-discharge, was determined for several western Iran watersheds, namely, in the catchments of Gamasiab, Qarasou, Saimare, Kashkan, Sezar and Abshineh. Daily data were prepared from stream-gauging stations and a 30-year concurrent period was selected.

 Flood frequency analysis was performed using HYFA and TR computer programs and optimum distributions were chosen by goodness of fit tests. Extreme flow values having different return periods of 2, 5, 10, 25, 50, 100, 500 and 1000 years were calculated. Modeling was done with regional analysis using multiple regression technique between maximum-daily mean-discharge and physiographic characteristics of the basins. The most important parameter for the selection of the model was the adjusted coefficient of determination while significant level, standard error and observed discharger vs. computed discharge plot acted as controlling parameters. Finally, different models with different parameters were selected from power, exponential, linear and logarithmic forms. The results showed the power model to be the best among the four types. The main channel length, drainage density and time of concentration were the most effective parameters on flow. After analyzing the errors, it appeared that increasing the return period would cause an increase in the model error. At 1000-year return period, the error reached 32.2%.


N. Mahboobi Soofiani, O. Farhadian,
Volume 6, Issue 4 (1-2003)
Abstract

To determine the effects of spawning frequency and density of incubating eggs on the survival rates of eggs and larvae in rainbow trout, five different groups of broodstocks with varying spawning frequencies were stripped. After fertilization, the percentage of survival at different stages of development, from eying, hatching to free swimming fry stages and also growth rates of larvae were determined. Moreover, the effects of incubating egg density (4000, 7000, 10000 per tray) on the different developmental stages of egg through free swimming larvae for each group of broodstock was studied. The study was carried out in a completely randomized design as a 5*5*3 factorial arrangement with three replicates. The results indicated that survival and growth rates are significantly correlated with spawning frequency (P<0.05) so that, survival and growth rates from fertilization to free swimming fry in broodstocks at their third and fourth spawning period were significantly different from the results obtained for broods in the first, second and fifth or higher spawning periods (P<0.05). Although the holding densities had no significant effects on the growth rate of larvae from different broodstocks, the survival rates from fertilization to free swimming stage was affected by incubating density so that the significantly lower value was recorded for density of 4000 per tray (P<0.05). In general, the results indicate that eggs obtained from broodstocks at their third and fourth spawning years have a better performance than those obtained from younger and older spawners. Also, the low holding density of eggs could decrease the performance of the fertilized eggs during incubating period.
S. S. Eslamian, A. Zarei, A. Abrishamchi,
Volume 8, Issue 1 (4-2004)
Abstract

An approach for regional low flow frequency analysis is to use multiple regression techniques for obtaining relationships between low flows with specific return periods and catchments characteristics. In this paper, this method has been used. After single-site frequency analysis for 20 stream gauging stations, homogeneity test was performed. Regional relationships between low flows with return periods 2 , 5 , 10, and 20 years and catchments characteristics were derived. For this purpose, catchment area, mean elevation, minimum elevation, shape factor, main channel length, length of main chanel from catchment centroid to outlet, forest area, mean annual rainfall, and mean catchment slope as model inputs were examined and cachment area, mean elevation, and mean catchment slope entered to the models. Finally, the mean relative error of models for different return period, 2, 5, 10, and 20 years, was computed 41.1, 41.3, 45.0, 47.2 percent, respectively that in comparison with other studies, it displays smaller errors.
B. Ghahraman, H. Abkhezr,
Volume 8, Issue 2 (7-2004)
Abstract

Rainfall intensity with different frequencies is needed for many hydrologic models. Rainfall intensity–duration–frequency relationships (IDF) have been investigated for different regions using previously recorded data. Iran Meteorological Organization has prepared IDF curves for 66 stations in Iran since which are the most updated data. Comprehensive IDF relationships were developed for these data. The results showed remarkable changes when compared with previous studies of Iran. This may be due to a change in parameters of probability distribution function as a result of increased record length of stations. Some relationships were also developed for ten year-hourly ( P6010) rainfall estimation from some parameters such as average annual rainfall and average maximum daily rainfall. Such a relationship was made for all stations and also for different classifications of regions (based on average annual rainfall and apparent climatically divisions). The validity of all relations was analyzed for eight independent stations with suitable spatial distribution. It was shown that all relationships are nearly valid as far as a suitable region is choosen. The previous relationship for Iran is not useful at present.
N. Davatgar, M. Kavoosi, M. H. Alinia, M. Paykan,
Volume 9, Issue 4 (1-2006)
Abstract

The soil potassium status and effect of soil physical and chemical properties on it were investigated using 109 surface soils (0-30cm) from four regions in Guilan province. Neutral molar ammonium acetate extractable K (K-NH4OAc), boiling molar nitric acid extractable K (K-HNO3) and water soluble K were determined. Results showed that CEC and clay were normally frequency distributed while distribution frequency of other variables such as silt organic carbon and pH were not normal and have significant skew and kurtosis. In addition sand, K-NH4OAc and K-HNO3 has logarithmic normal distribution. Water-soluble potassium was affected by sand, pH, O.C and K-NH4OAc (R2a=0.73**). Ammonium extractable potassium was affected by soluble potassium, non-exchangeable potassium and CEC (R2a=0.72**). Boiling nitric acid was affected by exchangeable potassium and silt (R2a=0.55**). Geographic distribution of K-NH4OAc data shows amount of it in central parts of Guilan, particularly Sepidrood river watershed is more than other regions. Fomanat region soils have the less clay, CEC, K-NH4OAc and K-HNO3. According this study about 68.8 percent of Guilan soils was classified in the range of medium to very low potassium status.
A. A. Azizi Zehan, A. A. Kamgar-Haghighi, A. R. Sepaskhah,
Volume 10, Issue 1 (4-2006)
Abstract

Iran with a cultivation area of 45000 ha and production of 150 ton/year is the number one saffron producer in the world. Planting of large size corms will increase flowering, but production of corms (number and size) may be affected by irrigation method or frequency. In this research which is performed in the farm of College of Agriculture, Shiraz University, the effects of method and frequency of irrigation on corm production, and the effect of produced corms on flowering were evaluated in two consecutive years. Two irrigation methods (basin and furrow) with four levels of irrigation frequencies (12, 24 and 36 days and dryland farming) were applied. In August of 2000 sample corm was taken from every plot, and the effect of applied treatment from previous growing period on corm production and the effect of produced corms on future flowering were evaluated and analyzed. Based on the results, in furrow irrigation, total number of corms and total number of corms smaller than 4 gr is significantly higher than basin irrigation. In all of the above cases, irrigation frequencies did not show a meaningful difference between themselves or in comparison with dryland farming treatment. Total weight of corms and number and weight of corms larger than 8 gr in basin irrigation were more than furrow irrigation. This is to the extent that it is considered as the main reason for the difference in the flowering of corms, and has caused the flowering of basin irrigation to be significantly higher than furrow irrigation. In basin irrigation, irrigation frequencies of 12 and 24 days had the highest amount of flowering. No significant difference was observed on average corm production between the treatments in the two irrigation methods. However, irrigation treatments in both irrigation methods showed significant differences when compared with dryland farming treatment. So, basin irrigation with irrigation frequency of 24 days is preferred over furrow irrigation due to lower water consumption and production of larger size corms which is effective in flowering.
J. Niazi, H. R. Fooladmand,
Volume 10, Issue 3 (10-2006)
Abstract

To investigate the effects of different irrigation levels on yield and oil content of rapeseed, and to determine the irrigation requirement and irrigation scheduling, an experiment with Randomized Complete Block Design consisting of four irrigation treatments replicated 3 times, was conducted in Zarghan Agric. Expt. Station during the years of 2000-2003. The treatments were based on the cumulative evaporation values of 50, 75,100 and 125 mm from class A pan (T50, T75, T100 and T125). The depth of water for each treatment was determined according to the deficit of field capacity and soil moisture content before irrigation. In the three years of experiment, the cultivars: Okapi, Orient and Likord were cultivated and the annual data related to yield and seed oil contents of each cultivar was analyzed separately. In the first year of experiment, the effect of different treatments on yield of Okapi cultivar was not significant, but the maximum and minimum yields were obtained at the T75 and T100 treatments equal to 2678 and 2050 kg ha-1, respectively. The effect of different treatments on seed oil content was significant at the level of 5 %, and the maximum and minimum seed oil contents were obtained at the T100 and T75 treatments equal to 42.50 and 41.66 %, respectively. In the second year of experiment, the effect of different treatments on the yield of Orient cultivar was significant at the level of 5 %, and the maximum and minimum yields were obtained at the T50 and T125 treatments equal to 3133 and 2133 kg ha-1, respectively. The effect of different treatments on seed oil content was significant at the level of 5 %, and the maximum and minimum seed oil contents were obtained at the T75 and T50 treatments equal to 46.38 and 44.82 %, respectively. In the third year of experiment, the effect of different treatments on the yield of Likord cultivar was significant at the level of 5 %, and the maximum and minimum yields were obtained at the T50 and T125 treatments equal to 3667 and 2250 kg ha-1, respectively. The effect of different treatments on seed oil content was significant at the level of 1 %, and the maximum and minimum seed oil contents were obtained at the T50 and T125 treatments equal to 47.63 and 44.60 %, respectively. Also, the best irrigation frequency for the three rapeseed cultivars in the Zarghan area was obtained equal to 10 to 12 days.
M. Loghavi, H. Rahimi,
Volume 11, Issue 40 (7-2007)
Abstract

A 4x4 factorial experiment with a completely randomized design with three replications was conducted separately on two major pistachio varieties, Ohady and Kaleghoochy, to investigate the effects of shaking amplitude and frequency on pistachio nut and cluster detachment. Four levels of shaking frequencies used for Ohady were 5, 7.5, 10 and 12.5 Hz, while those of Kaleghoochy were 7.5, 10, 12.5 and 15 Hz. Four levels of shaking amplitude for Ohady were 20, 40, 60 and 80 mm, while those of the Kaleghoochy were 40, 60, 80 and 100 mm. Analysis of variance and mean comparison showed that the effects of shaking amplitude and frequency on pistachio nut and cluster detachment were significant on both varieties. It was found that in Ohady, at frequency of 12.5 Hz and amplitude of 80 mm, the maximum effective nut detachment occurred. But considering the need to limit both yield loss and limb damage to 5% and minimizing the power requirement of the limb shaker, applying shaking amplitude of 60 mm and frequency of 10 Hz, which detaches 95% of the nuts, is considered as the most suitable combination of shaking amplitude and frequency. Also, at amplitude of 80 mm and frequency of 12.5 Hz, the highest percentage of cluster detachment occurred. Here again, by considering limb damage and power requirement, applying shaking frequency of 12.5 Hz at 60 mm amplitude with 69% cluster detachment was selected as the most suitable combination. In Kaleghoochi, at amplitude of 100 mm and frequency of 15 Hz, nut detachment was 100%, while the need to limit limb damage and power consumption, the combination of 60 mm amplitude and 15 Hz frequency with 97.2% nut detachment was selected as the most suitable one. For cluster harvesting of Kaleghoochy, shaking amplitudes of 60 and 40 mm and frequency of 12.5 Hz with cluster detachment of 75 and 69 percent, respectively were selected as the most suitable ones. The average ratio of tensile force required for removing pistachio nut to its weight (F/W), and the ratio of tensile force required for removing pistachio cluster to its weight (V/W), which could be considered as an index of ease of detachment, were measured 6.2 and 37 for Ohady and 9 and 37.8 for Kaleghoochy, respectively. Finally, we may conclude that by applying the suitable combination of shaking amplitude and frequency, shake harvesting of pistachio could be practiced successfully.
A. Goleij, H. Jalilvand, M. R. Pormajidian, M. Tabari, K. Mohammadi Samani,
Volume 11, Issue 41 (10-2007)
Abstract

In order to investigate the success of natural regeneration and to determine the best area for regeneration settlement, 12 gaps with the areas ranging from 50-100, 150-300, and 400-600 m2 and 4 replicates equal elevation level were selected. For measuring frequency, height, and collar diameter of regenerated seedlings, a certain number of 2 m2 subplots were carried out inside the gaps, along the bigger diameter, and related to each gap’s area. Results showed that the number of seedling varies from 5 (in big gaps) up to 28 (in small and moderate gaps) per square meter. Furthermore, there was not a significant difference between the number of seedlings in small and moderate gaps. In contrast, the number of seedlings in small and moderate gaps was significantly different from those in large gaps (at 1% Probability). This finding demonstrates that natural regeneration would be limited in large gaps (400-600 m2) but it shows a better result in smaller gaps, associated with single- tree harvests. The final result of this study shows that the most appropriate area for selective cuting in such an area is up to at most 300 m2.
A. Masoumi, A. Hemmat, M. Rajabi,
Volume 12, Issue 44 (7-2008)
Abstract

Due to yield increase, some farmers in Iran plant sugarbeet in 50-cm row spacing instead of conventional 60-cm row spacing. Low row spacings force farmers to harvest three consecutive rows instead of two alternate rows. This would increase the amount of draft requirement to pull the lifter through the soil. In order to use common medium tractors for pulling the three-unit sugarbeet lifter and properly lifting the sugarbeet tubers out of the soil, applying vibration to the shanks of the lifter was taken into considertion. In this study, the effects of vibration frequency and share rake angle of a vibratory lifter on its performance were investigated. Draft, slippage, percentage of broken and non-harvested tubers were determined for four vibration frequencies (0, 9, 10 and 12 Hz) and three share approach angles (11, 24 and 36 deg.), using a factorial experiment arrangement in a randomized complete block design with three replications. The results showed that the variations in draft and slip with frequency and rake angle were similar. Although the minimum value of draft resistance was obtained at 24 deg. of share rake angle with non-vibrated shanks, 50 percent of tubers remained in the soil and were not harvested. However, the non-harvested tubers reduced to only 20 percent when vibration was applied to the lifter. So using the vibrating shanks improved the removal of the tubers out of the soil. A ratio (K) of draft to the harvested tubers (whole and broken tubers) was defined for selecting the optimum combination of the rake angle and vibration frequency. The K ratio was calculated and analyzed for different combinations of the rake angle and vibration frequency. K ratio comparison showed that, for minimizing percentages of broken and non-harvested tubers, the sugarbeet lifter should have share rake angle of 24 deg. and vibrate with frequency of 9 Hz.
A Sarhadi, S Soltani, R Modaers,
Volume 12, Issue 46 (1-2009)
Abstract

Low flow estimation and its characteristics play an important role in hydrologic studies. However, some low flow events are ignored compared with the lowest annual low flow that may have high risk. These events are taken into consideration by the use of partial duration or peak over threshold models. In this study, a 7-day low flow was applied for frequency distribution and threshold, and the lower events were considered as the number of low flow event ( ) to study seasonal variation of low flows together with two graphical methods. The results showed two major low flow seasons, and for other times of the year, the low flow events are negligible. At last, the region was divided into homogeneous groups based on seasonal variation of low flows.
A. Shirzadi, K. Chapi, P. Fathi,
Volume 15, Issue 58 (3-2012)
Abstract

Estimation of flood hydrograph is of necessities in hydrological studies such as flood mitigation projects. This estimation in un-gauged watersheds is usually taken place using geomorphological characteristics of watersheds. The objective of this research is to estimate synthetic unit hydrograph using regional flood frequency analysis and geomorphological parameters of watersheds. 1-hour and 2-hour hydrographs of two watersheds, Kanisavaran and Maranj Watersheds, were generated using maximum discharge data based on regional flood frequency analysis. Estimated hydrographs were compared with observed data and the efficiency of the model was evaluated using Nash-Sutcliffe coefficient, absolute and bias errors. The results showed that multiple regression models give more acceptable results among others for the computation of synthetic unit hydrograph (higher coefficient of determination). The Nash-Sutcliffe coefficient was 0.98 for 1-hour hydrograph while it was 0.93 for the 2-hour hydrograph. The absolute error in 1-hour hydrograph and 2-hour hydrograph was 0.13 and 1.2, respectively. The bias error was close to zero for both hydrographs, indicating that the proposed model is efficient. The model may be used for estimation of synthetic unit hydrograph in similar un-gauged watersheds.
S. S. Eslamian, M. Ghasemi, S. Soltani Gerdefaramarzi,
Volume 16, Issue 59 (4-2012)
Abstract

In this study, in order to determe low flow conditions in Karkhe watershed, 5 indices of Q7,10, Q7,20, Q30,10, Q4,3 and Q95 were used for analyzing 12 hydrometric station data in the years of 1345-46 to 1380-81. Discharge data homogeneity was performed by Run Test. The Q95 index was determined by flow duration curve (FDC) and other indices were determined using 4, 7 and 30-day low flow frequency analysis. After calculating the indices, periods of low flows were determined. The indices were regionalized by Kriging method. The results showed that for the most stations, low stream flows happened in the years of 1345-46, 1377-78, 1378-79, 1379-80 and 1380-81 and the percentages of stations having low flows in these years were 68, 92, 84, 75 and 59, respectively. According to the regional maps of low flows in Karkhe watershed, maximum low flows are located in central and southern areas and all of the mentioned indices decrease from south to the north of this watershed.
M. Erfanian, H. Farajollahi, M. Souri, A. Shirzadi,
Volume 20, Issue 75 (5-2016)
Abstract

The aim of this study is to prepare the groundwater spring potential map using Weight of Evidence, logistic regression, and frequency ratio methods and comparing their efficiency in Chehlgazi watershed, province of Kurdistan. At first, 17 effective factors in springs occurrence including geology, distance to fault, fault density, elevation, relative permeability of lithological units, slope steepness, slope aspect, plan curvature, profile curvature, precipitation, distance to Stream, drainage Stream density, Sediment Transport Capacity Index (STCI), Stream Power Index, topographic wetness index (TWI) and land use/land cover (LU/LC) were selected. The validation processes of methods were conducted by relative performance characteristic curve (ROC). The area under an ROC curve (AUC) for the weight of evidence, logistic regression and frequency ratio was 85/8%, 79% and 89%, respectively. The results showed that all methods are suitable estimator for mapping the groundwater spring potential in the study area. But the frequency ratio method with the most amounts is the best method to produce and map the groundwater spring potential. Also, validation of the mappings based on the percentage of pilot springs, training springs and all springs showed that the logistic regression, WoE and frequency ratio, with 45, 56 and 45 percent of spring occurrence on the high potential classes respectively, had the highest validation.


S. Chavoshi,
Volume 22, Issue 4 (3-2019)
Abstract

Regional flood frequency studies are initialized by the delineation of the homogeneous catchments. This study was based on "Region of Influence" concept, aiming to find the similar catchments in the south of Caspian Sea. The methodology utilized the Particle Swarm Optimization Algorithm, PSO, to optimize the fuzzy system over a dataset of catchment properties. The main catchment variables in relation to flood were determined by the principle component analysis method and employed as the inputs in the fuzzy system. Catchments grouping was performed over these fuzzy input variables by the iterative process. The optimum similar groups were obtained by PSO, and the heterogeneous L-moment index was used as the termination criterion for the optimization process. A total of 61 hydrometric stations located in the study area were selected and their relevant catchments' physical, climatic and hydrologic properties in relation to flood were studied. Principle Component Analysis by Variomax Rotation Factor over the catchments datasets tended to four out of 16 physical variables, including area, mean elevation, Gravelious Factor and Form Factor, as the main parameters in terms of homogeneity with 84 percent of accumulative variance. These variables, as well as mean annual rainfall, were used as the input data to define the fuzzy system. PSO algorithm was then employed to optimize the developed fuzzy system. The developed algorithm tended to yield the best result in the 9th iteration with 26 and 22 for the minimum average and the optimum values of cost function, respectively. The topology of the resulting algorithm included inertia weight, local and acceleration rates, the number of generations and population size, with the values of 0.7298, 1.4962, 1.4962, 10 and 5, respectively. This study tended to a total of 61 regions of influence, proportional to the relevant 61 sites. According to the geographical location of the catchments in the region, it could be concluded that the geographical proximity doesn't necessarily involve homogeneity. The obtained results indicated the efficient potential of PSO-FES in the delineation of the homogenous catchments in the study area.

S. Chavoshi Borujeni, K. Shirani,
Volume 24, Issue 3 (11-2020)
Abstract

Selection of the appropriate distribution function and estimation of its parameters are two fundamental steps in the accurate estimation of flood magnitude. This study relied on the concept of optimization by meta heuristic algorithms to improve the results obtained from the conventional methods of parameter estimation, such as maximum likelihood (ML), moments (MOM) and probability weighted moments (PWM) methods. More specifically, this study aimed to improve flood frequency analysis using the Artificial Bee Colony algorithm (ABC). The overall performance of this algorithm was compared to the conventional methods by employing goodness of fit statistics, correlation coefficient (CC), coefficient of efficiency (CE) and root mean square error (RMSE). The study area, Babolrood catchment located in southern bank of Caspian Sea, has been subjected to annual flooding events. A total of 6 hydrometry stations in the study area were delineated and their data were used in the analysis of 6 distribution functions of Normal, Gumbel, Gamma, Pearson Type 3, General Extreme Value and General Logistic. This analysis indicated that Gamma and Pearson Type 3 were the most appropriate distribution functions for flood appraisal in the study area, according to the ABC and conventional methods, respectively. Also, the results showed that ABC outperformed ML, MOM and PWM; so, Gamma could be recommended as the most reliable distribution function for flood frequency analysis in the study area.

S. Farhadi, M. Galoie, A. Motamedi,
Volume 26, Issue 1 (5-2022)
Abstract

One of the important relationships which are used in the estimation of river discharges and floods is Intensity-Duration-Frequency (IDF). The accuracy of this relation is dependent on the accuracy of its parameters which need to be found based on short-duration rainfall depths (such as 15, 30, 60 minutes, and so on) for a long term (i. e. 30 consecutive years). Unfortunately, only 24-hour rainfall depths are available in many rainfall stations in Iran. Various empirical relations are available to convert 24-hour rainfall depth to sub-daily. One of these methods is IMD and its accuracy in some regions is low. In this research, the IMD method was transformed into a single-parameter equation and then, this parameter is evaluated for some rainfall stations in Iran. To do this, maximum 24, 12, 6, and 3-hour rainfall depths were extracted and their frequencies were calculated using Weibull and Gumbel methods. Regional coefficients in the modified IMD method were estimated using a linear regression method. Although the power of the IMD method is 0.33, results showed that this parameter for the rainfall stations ranged from 0.28 to 0.35. To make more comparison, the IDF relation of Kordan’s watershed was calculated using the short-duration rainfall depth which was estimated using the modified IMD, and then, this IDF was compared to observed data and Ghahraman’s relation which is commonly used in Iran. The comparison showed that the modified IMD relation could estimate the short-duration rainfall data better than Ghahraman’s relation. After calibration of the modified IMD relation for various regions in Iran, the sub-daily rainfall depth can be obtained with high accuracy.

F. Naeimi Hoshmand, F. Ahmadzadeh Kaleybar,
Volume 26, Issue 3 (12-2022)
Abstract

Hydrological models for evaluating and predicting the amount of available water in basins, flood frequency analysis, and developing strategies to deal with destructive floods are expanding daily. In this study, HEC-GeoHMS and Arc Hydro extensions in ArcGIS software and the HEC-HMS model were used to simulate design flood hydrographs in the Aydooghmush basin in the northwest of Iran. SCS-CN, SCS-UH, Maskingham, and monthly fixed methods were used to calculate rainfall losses, rainfall-runoff transformation, flood routing, and base flow, respectively. In model calibration with two real flood events, the average of absolute values of the residuals, the sum of the remaining squares, and the weight of the peak mean the error squares for the flood volume were 2.75, 5.91, and 5.32, respectively and for peak discharge were 8.9, 8.0, and 8.0, respectively. Model validation was evaluated as acceptable with a one percent error rate in the peak of discharge and a 19 percent in the flood volume. For maximum 24-hour precipitation, the log-Pearson type 3 was determined as the most suitable distribution in the SMADA model and design precipitation was extracted in different return periods. Thus, for the return period of 2 to 1000 years, the peak discharge and volume of the design flood were simulated equally to 18.8 to 415.6 m3 s-1 and 5.7 to 87.9 MCM, respectively.


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