Log Pearson Type Research Articles

ANALISIS STABILITAS BANGUNAN PENGENDALI SEDIMEN PADA KONDISI BANJIR RANCANGAN DAN TAMPUNGAN SEDIMEN PENUH : SUATU KASUS DI ARBORETUM SUMBER BRANTAS, KOTA BATU

The level of land-use change in the Brantas watershed includes encroachment in the upstream area of the spring which has been increasingly massive since the 1960s, and reached the highest level in the late 1990s which driving the watershed damage. The damage in the upstream area encourages the need to increase resilience by building The Sumber Brantas Arboretum Area. This area is equipped with sedimentary control structures to ensure the long-term sustainability of the arboretum. A recent study of the rainfall plan and the security level of the sedimentary control building to the arboretum became an interesting thing to be reviewed. The analytical approach used in this study is quantitative. The method used for flood design analysis uses three methods including Log Pearson Type III Method, Gumbel Method, and Iwai Method. The selected hydrograph is the Nakayasu Hydrograph. Hydraulics analysis of sediment control buildings using HEC-RAS tools with several other hydrological calculations. The results of the analysis in the Sumber Brantas Arboretum Area showed that the design flood discharge (Q) was 59.35 m3 / sec. In flood design conditions with its own weight, the åf of the sediment control building is 42.2 (higher than the minimum safety level) and it is relatively safe, either in normal or in an earthquake condition. In the design flood conditions with full sediment storage, the Sf of sediment control buildings is 1.6 (higher than the minimum safety level) so that it is relatively safe, either in normal or in an earthquake condition.

Rainfall-Runoff Simulation Using HEC-HMS Model in the Benanain Watershed, Timor Island

Floods in a watershed area are caused by reduced water recharge due to changes in land use, increasing their discharge volume. Benanain watershed is an extensive area with many tributaries. Watershed morphometrics provides initial information about the hydrological behavior and the hydrograph shape of flooding in these areas. Furthermore, rainfall-runoff modeling uses as a unit to approach the hydrological values of the flooding process. This study determines the physical characteristics of the Benanain watershed based on curve number (CN) values, land cover, peak discharge, and peak time. It was conducted on the Benanain watershed with 29 sub-watersheds covering 3,181.521 km2. Data were collected on the rainfall experienced for 13 years from 1996 to 2008 and analyzed using the Log Pearson Type III method, while the HEC HMS model was used for flood discharge analysis. HEC-HMS model must calibrate by adjusting the model parameter values until the model results match historical data such as initial abstraction, lag time, recession, baseflow values, and curve number. The results show that the curve number values range from 56.55 - 73.90, comprising secondary dryland forest and shrubs. Moreover, the rock lithology in the Benanain watershed is dominated by scaly clay and other rock blocks. This means the area has low to very low permeability, which affects the volume of runoff. The return period of a 1000-year flood discharge obtained a peak of 5,794.50 m3/s, with a peak time of ± 14 hours. Morphometry of the Temef watershed with large catchment, radial shape pattern, an average of steep slope river, and meandering affects the peak of flood discharge hydrograph and the peak time of the flood.

Selection of suitable PDF model and build of IDF curves for rainfall in Najaf city, Iraq

The models of the Intensity-Duration-Frequency (IDF) curves relationship is considered a significant represents of the rainfall intensities used in the water resources structures, in the planning, designing and projects operation. This paper aims to estimate the Intensity-Duration-Frequency (IDF) curves and find the equations of these curves for AL-Najaf city, Iraq. Also, to identify the distribution that gives the highest rainfall intensities from the three commonly distributions used in this field. The (IDF) curves explain the relationship between the rainfall intensity and different return intervals. The study investigates the maximum daily rainfall data of 30 years using the Indian Meteorological Department (IMD) empirical formula to calculate the short durations rainfall intensity for 5, 10, 20, 30, 60 and 120 minutes, and with return periods of 2, 5, 10 and 25 years. The frequency analysis, which involves various statistical distributions, have been used to developing the relationship between rainfall intensities, durations, and return periods. The frequency analysis build based on the maximum daily rainfall data of the choosing interval (1989-2018), which had collected from the Meteorology and Seismic Monitoring Authority of Iraq. The used distributions are Gumbel, Lognormal and Log Pearson Type III distribution. The technique of the non-linear analysis has used to get the (IDF) curves equations. Also, Easy-fit software 5.5 involve the Kolmogorov-Smirnov test, which used to test the goodness of fit. The results showed that Gumbel distribution gave the best rainfall intensities for different return periods and different durations, where calculated rainfall intensities by Gumbel distribution had the highest values between the three applied distributions in this paper. The high values are more reliable to avoid the higher risks caused by sewer systems floods due to higher rainfall intensities due to climate change.

Analysis of the impact of various vertical release patterns on the atmospheric dispersion and total deposition of 137Cs from Chernobyl Nuclear Power Plant accident.

The Chernobyl Nuclear Power Plant (NPP) catastrophe of 1986 has been a milestone in the use of nuclear power for energy generation. After the accident, various topics have been discussed to evaluate the details of occurrence of the event and to understand its impacts on human, animal and plant life. One of the most controversial topics is the release height and homogeneity of radionuclides at release point in the atmosphere. Currently, there exists no definitive decision on the release height and vertical distribution pattern of radionuclides released from the Chernobyl accident. Based on this premise, this study focuses on the analysis of various possible release patterns along the vertical dimension and the potential influences on the atmospheric dispersion and total deposition with particular reference to 137Cs. For this purpose, some release pattern functions following uniform, Dirac delta, exponential, log-Pearson type III, and cumulative distribution functions along the z-axis were used to simulate the dispersion of 137Cs released from the accident site. A total of 22 release patterns are produced using different maximum release heights (2000, 3000, and 4000 m). A Lagrangian particle dispersion model, FLEXPART, was then used to conduct simulations for these conditions to assess most coherent dispersion and deposition patterns. Model results from each release function were plotted, compared with each other and verified with measured data. In the functions where the release predominantly existed at lower levels, more extreme values were observed in the close vicinity of the source. Consequently, Dirac delta, log-Pearson type III (1), and exponential functions can be used as worst-case conditions at local scale. On the other hand, simulations also revealed that contamination spread to wider areas in cases where the release occurred from higher levels of the atmosphere. Therefore, log-Pearson type III (2) and cumulative distribution function can be considered more significant concerning a wider distribution of affected areas.

An investigation of prospective current power generation with the log Pearson type 3 distribution in the upper layer in the vicinity of the Northern Bosphorus

The main purpose of this research was to develop general equations that can be used to estimate the mean and standard deviation of the current power by using perturbation theory. The developed formulae herein can be applied to current data that fit the log Pearson type 3 probability distribution function. By using the fitted parameters of the distribution (shape, scale, and location parameters), the mean and standard deviation of the current power can be estimated more accurately. The developed equation was applied at a location in the vicinity of the Northern Bosphorus. Finally, the maximum power density and energy obtained were 21.24 W/m2 and 186.19 kW h/m2/year, respectively.

Study of Unbiased Plotting Position Formulae for the Generalized Extreme Value (GEV) Distribution

The determination of appropriate quantile relations between the magnitude of extreme events and the corresponding exceedance probabilities is a prerequisite for optimum design of hydraulic structures. Various plotting position formulae have been proposed for estimating the exceedance probabilities or recurrence in. In this study, eight plotting position formulae recommended for GEV distribution were used for estimating the exceedance probabilities of annual maximum series of River Niger at Baro, Kouroussa and Shintaku hydrological stations. The performance measures of PPCC, RRMSE, PBIAS, MAE and NSE were calculated by applying their individual equations to each pair of observed AMS, arranged in ascending order, and exceedance probabilities calculated using each plotting positions. The result of the study show that Weibull was the best plotting position formula, seconded by Beard and thirdly, In – na and Ngugen. This study underscores the necessity to accurately size water infrastructure. In a recent paper, the author found GEV distribution the best – fit probability distribution model in Nigeria. Thus, the need to develop indepth understanding and accurate estimation of exceedance probabilities and return periods using the GEV distribution. Furthermore, this paper recommends similar studies to be conducted for Pearson Type 3(PR3) and Log Pearson Type 3 (LP3) distributions.

Study of Unbiased Plotting Position Formulae for the Generalized Extreme Value (GEV) Distribution

The determination of appropriate quantile relations between the magnitude of extreme events and the corresponding exceedance probabilities is a prerequisite for optimum design of hydraulic structures. Various plotting position formulae have been proposed for estimating the exceedance probabilities or recurrence in. In this study, eight plotting position formulae recommended for GEV distribution were used for estimating the exceedance probabilities of annual maximum series of River Niger at Baro, Kouroussa and Shintaku hydrological stations. The performance measures of PPCC, RRMSE, PBIAS, MAE and NSE were calculated by applying their individual equations to each pair of observed AMS, arranged in ascending order, and exceedance probabilities calculated using each plotting positions. The result of the study show that Weibull was the best plotting position formula, seconded by Beard and thirdly, In – na and Ngugen. This study underscores the necessity to accurately size water infrastructure. In a recent paper, the author found GEV distribution the best – fit probability distribution model in Nigeria. Thus, the need to develop indepth understanding and accurate estimation of exceedance probabilities and return periods using the GEV distribution. Furthermore, this paper recommends similar studies to be conducted for Pearson Type 3(PR3) and Log Pearson Type 3 (LP3) distributions.

Analisis Saluran Drainase di Pemukiman Padat Penduduk

Flooding is a common problem in society. Floods and puddles in densely populated areas often occur due to damage to drainage channels. Floods can also occur when conditions of high rainfall. The purpose of this research is to evaluate the causes of flooding and to analyze the capacity of the drainage channel for densely populated settlements on Lio Santa, Citamiyang Village, Sukabumi City. Cibareno. The rainfall used for this hydrological analysis is data on the 10-year return period, from 2011 to 2020. The topographic maps used were obtained from Balai PSDA Ws. Cisadea-Cibareno and land use maps from the Sukabumi City BAPPEDA service, processing topographic data using the software. AutoCAD and land use using ArcGIS software. Rain frequency analysis used is the Moment method, with a quantitative measure of the geometric system of the Normal distribution, Lognormal distribution, Gumbel distribution, and Log Pearson type III distribution. The results of the analysis show that the most suitable distribution uses the Log Pearson Type III distribution based on the compatibility of the Chi-Square and Smirnov-Kolmogorov tests. The calculation of the discharge intensity of the drainage channel plan uses the Rational Method of the 10-year return period equation method for channel size. The results of the design discharge analysis of the channel are obtained at Q_plan = 0.663 m³/s and the existing drainage capacity of the canal (b = 0.6m) and (h = 0.6m) is Q_existing = 0.454 m³/s. So the comparison of the discharge is obtained that the design discharge is greater than the existing Q_plan > Q_existing, so it is necessary to redesign the drainage system by increasing the dimensions of the drainage channel until the optimal capacity is obtained. The results of the drainage analysis are obtained (b = 1m) and (h = 1m) with a flow rate of Q_ accommodate= 0.786 m³/s and Q_plans= 0.663 m³/s so that the drainage canal is able to accommodate the planned discharge capacity of the 10-year return period. As for suggestions for other countermeasures that can be used in addition to changing the dimensions of the channel, namely by making a Water Infiltration System Building, because making infiltration wells is very suitable for making wells it does not take up a large area of ​​land then the soil structure of residential areas that absorbs quickly is very adequate, it is known from the runoff coefficient (C) of 0.30.

The Use of a Uniform Technique for Harmonization and Generalization in Assessing the Flood Discharge Frequencies of Long Return Period Floods in the Danube River Basin

The flow regime conditions of the Danube River are continually changing. These changes are the result of natural processes and anthropogenic activities. The territory of the Danube River Basin is one of the most flood-endangered regions in Europe and assessing the design discharges along the Danube channel is complicated by the different estimation methods that are applied in particular countries. For this reason, it is necessary to harmonize flood design value assessment methods. The long-term maximum annual discharge series of the Danube River and other rivers in the Danube basin were analyzed and used to estimate the flood design values. We used the Log-Pearson type III distribution, which is one of the most widely used theoretical probability distributions to estimate extremes. This distribution can be flexibly applied to extreme values depending on the skew coefficient. We also analyzed the effect of the inclusion and exclusion of the historical extremes in the processed dataset. The results show that the inclusion of historical floods and the regionalization of the Log-Pearson type III distribution skew parameter can change the design discharges.

Study on Flood Simulation of Tallo Watershed, Makassar City, South Sulawesi Province

Tallo watershed has a length of 70 km, its area width is 407.00 ¬¬km2, the river upstream or downstream is at an altitude of ± 1,100 m above sea level located on Mount Kaliapolompo in which the overall length of the river in Tallo watershed totaling ± 131.50 km2. The research objective was to analyze the effect of five-year flood discharge and tidal changes on the inundation area and flood depth in Tallo watershed. The method of rainfall analysis used the Log Pearson type III method where the flow is considered to be two horizontal dimensions with even velocity at each depth. A five-year period with a discharge value of 127.64 m3/s will statistically reoccur every five years with an estimated chance of occurrence of 0.2 or 20% for each year referred to in a 5-year review cycle. The results of the simulation were then known that the five-year flood discharge resulted in flooding with a depth of 0-3 meters from the maximum tide condition (HWSL), and an inundation area of 31.91 km2 inundated the Tallo District, Tamalanrea District, Panakukang District, West Biringkanaya District and northern Manggala District. These areas are located on the left and right of the Tallo River with an altitude between 0 and 2 meters above sea level.

Flood Flow Probability Distribution Model Selection on Niger/Benue River Basins in Nigeria

Flood frequency analysis is a crucial component of flood risk management which seeks to establish a quantile relationship between peak discharges and their exceedance (or non-exceedance) probabilities, for planning, design and management of infrastructure in river basins. This paper evaluates the performance of five probability distribution models using the method of moments for parameter estimation, with five GoF-tests and Q-Q plots for selection of best –fit- distribution. The probability distributions models employed are; Gumbel (EV1), 2-parameter lognormal (LN2), log Pearson type III (LP3), Pearson type III(PR3), and Generalised Extreme Value( GEV). The five statistical goodness – of – fit tests, namely; modified index of agreement (Dmod), relative root mean square error (RRMSE), Nash – Sutcliffe efficiency (NSE), Percent bias (PBIAS), ratio of RMSE and standard deviation of the measurement (RSR) were used to identify the most suitable distribution models. The study was conducted using annual maximum series of nine gauge stations in both Benue and Niger River Basins in Nigeria. The study reveals that GEV was the best – fit distribution in six gauging stations, LP3 was best – fit distribution in two gauging stations, and PR3 is best- fit distribution in one gauging station. This study has provided a significant contribution to knowledge in the choice of distribution models for predicting extreme hydrological events for design of water infrastructure in Nigeria. It is recommended that GEV, PR3 and LP3 should be considered in the development of regional flood frequency using the existing hydrological map of Nigeria.

Flood frequency analysis of Casimcea river

Flood frequency analysis is the most important statistical technique in understanding the nature and magnitude of high discharge in a river. This technique is used for establishing a relationship between flood magnitude and frequency of occurrence (return period). This study performs the flood frequency analysis of Casimcea river. The Casimcea catchment is located in the Dobrogea-Littoral basin of south-eastern Romania, and covers parts of two counties, Tulcea and Constanta. The main river of Casimcea catchment flows into the Tasaul lake and has two main tributaries (Ramnic and Cartal). In this study, Log-Normal, Log-Pearson Type III and Gumbel probability distributions have been applied on maximum discharge time series data of four hydrological stations, Casimcea and Cheia on Casimcea River and Pantelimonu on its main tributaries Ramnic and Cartal. For this study have been used the annual maximum series data spreading from 29 to 52 years. The frequency analysis will be performed with Hydrognomon. open-source software for the analysis of hydrological data. Hydrognomon is free software licensed under the General Public License (GPLv3).

THE BEST FIT PROBABILITY DISTRIBUTION MODEL FOR THE ESTIMATION OF EXTREME RAINFALL IN LIMBANG, SARAWAK

In Malaysia, the increment of annual rainfall patterns is causing frequent floods, mainly in Sabah and Sarawak.Limbang river basin was selected as a case study due to it was facing of high-risk flooding problem mainly during the transition of climate. This study was aimed to estimate the frequency of rainfall under various return periods and to identify the best fit model probability distribution of annual maximum rainfall based on twenty-four hours sample in Limbang. The three statistical models were used, which are Gumbel, Log-Pearson type III, and Log-Normal. Based on the goodness of fit tests, Chi-Square, Kolmogorov Smirnov test, and the Log-Normal was found to be the best fit model for the station of Panduran. The Log-Pearson type III was found to be the best-fit distribution model for the rest of the stations, which occupies almost more than 90%. The maximum values of expected rainfall were calculated using the best fit probability distributions and could be used by a design engineer in the future.Keywords: flood, return period, Gumbel distribution

Selection of the best probability models for daily annual maximum rainfalls in Egypt

Twelve commonly used probability distributions are evaluated to identify the most suitable model that could provide accurate extreme rainfall estimates in Egypt. Three popular parameter estimation methods are applied: the method of moments, L-moments and maximum likelihood. The performance of the models is evaluated based on several numerical and graphical goodness-of-fit criteria. The proposed procedure is applied to annual maximum daily rainfall data from a network of 31 stations located in Egypt. The results indicate that no single distribution performed the best at all stations. Log-Normal, Log-Pearson Type III and Exponential are the top three distributions for the frequency analysis of daily annual extreme rainfalls in Egypt, i.e. they are selected as the “optimum” models for 23%, 19% and 19% of the total stations, respectively. In contrast, the distributions: Normal, Gumbel, Logistic and Generalized Logistic are not suitable for describing the extreme rainfalls in the country. The performances of both L-moments and maximum likelihood methods are almost equal and much better than that of the method of moments. Additionally, Depth-Duration-Frequency curves were established for 18 stations by using the “optimum” model, which can support the design of hydraulic structures. The findings from this study would be helpful for rainfall frequency analysis in similar arid countries.

Predictive Performance Analysis of PDF – IDF Model Types Using Rainfall Observations from Fourteen Gauged Stations

The design of structures for flood mitigation depends on the adequate estimation of rainfall intensity over a given catchment which is achieved by the rainfall intensity duration frequency modelling. In this study, an extensive comparative analyses were carried out on the predictive performance of three PDF – IDF model types, namely: Gumbel Extreme Value Type 1 (GEVT – 1), Log-Pearson Type 3 (LPT – 3) and Normal Distribution (ND) in 14 selected cities in Southern Nigeria. This is to rank the order of best performance. The principle of general model development was adopted in which rainfall intensities at different durations and specified return periods were used as input data set. This is not same as return period specific model that involves rainfall intensities for various durations and a given return period. The predicted rainfall intensity values with the PDF – IDF model types indicate high goodness of fit (R2) and Mean Squared Errors (MSE) ranging from: (a) R2 = 0.875 – 0.992; MSE = 33.17 – 224.6 for GEVT – 1; (b) R2 = 0.849 – 0.990; MSE = 65.34 – 405.5 for LPT – 3 and (c) R2 = 0.839 – 0.992; MSE = 29.23 – 200.2 for ND. The comparative analysis of all the 42 general models (14 locations versus 3 model types) considered showed that the order of best performance is LPT – 3 1st, GEVT - 1 2nd and ND 3rd for each return period (10, 50 and 100 years). The Kruskal Wallis test of significance indicates that no significant difference exists in the predictive performance of the three General models across the board. This may be due to the fact that the fourteen locations of the study area are bordering with the Atlantic Ocean and seems to have similar climatology. These developed General models are recommended for the computation of intensities in the fourteen locations for the design of flood control structures; and the order of preference should be LPT – 3 > GEVT – 1 > ND.

ASSESSMENT OF THE BEST PROBABILITY DISTRIBUTION METHOD IN RAINFALL FREQUENCY ANALYSIS FOR A TROPICAL REGION

The Intensity-Duration-Frequency (IDF) curve defines the relationship between rainfall intensities at certain durations and with the frequencies. The IDF Curve is extensively used in many applications such as flood modelling and peak discharge estimation. Over the years, the frequent occurrence of flood has become a great challenge in Kelantan river basin. Herein, IDF curves using frequency analyses based on different distributions were developed and compared. The historical rainfall data at eight rainfall stations for the period of 1985-2019 were selected for the assessment purpose. The Gumbel, Normal and Log Pearson Type III distributions were fitted into the annual maximum rainfall series for durations varying from 30 minutes to 24 hours. The goodness of fit tests were then used to evaluate the performances of each frequency distribution. It was found that the Gumbel distribution gave the highest passing rate followed by the Log Pearson Type III and then the Normal distributions. The Gumbel distribution resulted in respective 86% and 75% passing rate since most of the p-values generated by both the K-S and the Mann-Whitney test were greater than 5% of significance level leading to the acceptance of the null hypothesis. Thus, the Gumbel distribution is suggested for the frequency analyses in this study.

ANALISIS DEBIT BANJIR DAN DINDING PENAHAN PADA HILIR SUNGAI NGOTOK DI KOTA MOJOKERTO

The Ngotok River in Mojokerto City has a length of 25 km and an area of ​​269.87 km2 of watershed. At the downstream side of the riverbank, marine tourism and green open spaces will be built. This study aims to determine the discharge in the Ngotok River with a return period of 50 years and to anticipate overflows in the riverbank area. The data needed is Rainfall Data for 5 Rain Stations, namely Jombang, Kesamben, Sambiroto, Mojoagung and Terusan 2009 to 2018. Determining the correctness of rainfall data using the multiple mass curve method. In the design of rainfall planning using the algebraic average method while the regional rainfall planning uses the Log Pearson type 3 method. To strengthen the selection of the distribution taken using the Chi-square test distribution test and the Smirnov-Kolmogorov test. Furthermore, the planned flood discharge analysis was carried out using the HSS Nakayasu method. Based on the calculation, it was found that the flood discharge of Buntung River with a 50 year return period was 624,766 m3 / second. River improvement planning uses the HEC-RAS model with the results of overtopping areas at points P1-10, P40, P30, P14, P13, P5 and P2. The control building is a concrete sheet pile W-600 B.

A comparison between generalized least squares regression and top-kriging for homogeneous cross-correlated flood regions

ABSTRACT Spatial cross-correlation among flood sequences impacts the accuracy of regional predictors. Our study investigates this impact for two regionalization procedures, generalized least squares (GLS) regression and top-kriging (TK), which deal with cross-correlation in two fundamentally different ways and therefore might be associated with different accuracy and uncertainty of predicted flood quantiles. We perform a Monte Carlo experiment based on a dataset of annual maximum flood series for 20 catchments in a hydrologically homogeneous region. Based on a log-Pearson type III parent distribution, we generate 3000 realizations of the region with different degrees of cross-correlation. For each realization, GLS and TK are applied in leave-one-out cross-validation to predict at-site flood quantiles. Our study shows that (a) TK outperforms GLS when catchment area is the only catchment descriptor used for predicting “true” population (theoretical) flood quantiles, regardless of the level of cross-correlation, and (b) GLS and TK perform similarly when multiple catchment descriptors are used.

Comparative Evaluation of Probability Distribution Models of Flood flow in Lower Niger Basin

The choice of optimum probability distribution model that would accurately simulate flood discharges at a particular location or region has remained a challenging problem to water resources engineers. In practice, several probability distributions are evaluated, and the optimum distribution is then used to establish the quantile - probability relationship for planning, design and management of water resources systems, risk assessment in flood plains and flood insurance. This paper presents the evaluation of five probability distributions models: Gumbel (EV1), 2-parameter lognormal (LN2), log pearson type III (LP3), Pearson type III(PR3), and Generalised Extreme Value (GEV) using the method of moments (MoM) for parameter estimation and annual maximum series of five hydrological stations in the lower Niger River Basin in Nigeria. The choice of optimum probability distribution model was made on five statistical goodness – of – fit measures; modified index of agreement (Dmod), relative root mean square error (RRMSE), Nash – Sutcliffe efficiency (NSE), Percent bias (PBIAS), ratio of RMSE and standard deviation of the measurement (RSR), and probability plot correlation coefficient (PPCC). The results show that GEV is the optimum distribution in 3 stations, and LP3 in 2 stations. On the overall GEV is the best – fit distribution, seconded by PR3 and thirdly, LP3. Furthermore, GEV simulated discharges were in closest agreement with the observed flood discharges. It is recommended that GEV, PR3 and LP3 should be considered in the final selection of optimum probability distribution model in Nigeria.

Comparative Evaluation of Probability Distribution Models of Flood flow in Lower Niger Basin

The choice of optimum probability distribution model that would accurately simulate flood discharges at a particular location or region has remained a challenging problem to water resources engineers. In practice, several probability distributions are evaluated, and the optimum distribution is then used to establish the quantile - probability relationship for planning, design and management of water resources systems, risk assessment in flood plains and flood insurance. This paper presents the evaluation of five probability distributions models: Gumbel (EV1), 2-parameter lognormal (LN2), log pearson type III (LP3), Pearson type III(PR3), and Generalised Extreme Value (GEV) using the method of moments (MoM) for parameter estimation and annual maximum series of five hydrological stations in the lower Niger River Basin in Nigeria. The choice of optimum probability distribution model was made on five statistical goodness – of – fit measures; modified index of agreement (Dmod), relative root mean square error (RRMSE), Nash – Sutcliffe efficiency (NSE), Percent bias (PBIAS), ratio of RMSE and standard deviation of the measurement (RSR), and probability plot correlation coefficient (PPCC). The results show that GEV is the optimum distribution in 3 stations, and LP3 in 2 stations. On the overall GEV is the best – fit distribution, seconded by PR3 and thirdly, LP3. Furthermore, GEV simulated discharges were in closest agreement with the observed flood discharges. It is recommended that GEV, PR3 and LP3 should be considered in the final selection of optimum probability distribution model in Nigeria.