Vol. 13(1), pp. 30-36, January-March, 2021 DOI: 10.5897/IJWREE2020.0936 Article Number: 3962E7465930 ISSN 2141-6613 Copyright©2021 International Journal of Water Resources and Author(s) retain the copyright of this article http://www.academicjournals.org/IJWREE Environmental Engineering Full Length Research Paper Flood frequency analysis of River Niger at Lokoja, Kogi State using Log-Pearson Type III distribution Ahuchaogu Udo E.1*, Ojinnaka O. C.2, Njoku R. N.1 and Baywood C. N.1 1Department of Surveying and Geo-Informatics, Federal University of Technology, Owerri, Imo State, Nigeria. 2Department of Geo-informatic, and Surveying, University of Nigeria, Enugu Campus, Enugu State, Nigeria. Received 9 June, 2020; Accepted 4 September, 2020 This study applied Log-Pearson Type III probability distribution to model time series annual peak flow records of River Niger recorded at Lokoja gauging station. This was necessitated by the need to provide reliable data for safe and economic hydrologic design for security of lives and property at downstream of river Niger basin. Though several methods have been adopted in the study area for flood mitigation, however, it has become apparent that these measures are inadequate and no attempt has been made to apply statistical approach for provision of sustainable solution. Though flood cannot be prevented but the impact can be reduced by applying adequate counter measures. Therefore, this study shows the result of flood frequency analysis based on annual peak flow measurement covering a period of 18 years (1995-2012) carried by National Inland Water Ways (NIWA) at Lokoja gauge station. The probability distribution function was applied to return periods (T) of 2, 5, 10, 25, 50, 100 and 200 years. The predicted discharges corresponding to these return periods are 18886.065, 22425.127, 24889.683, 28145.456, 30670.104, 33281.363 and 35997.757 m3/s, respectively. This study also revealed that the return period of 2012 flood is over 50 years. The predictive model which relates the expected discharge to return period is given by X = 3679.7 In(R) + 16381 where X is the expected discharge and R is the return period. Key words: Flood, return periods, discharge, prediction, hydrologic design. INTRODUCTION Flooding is one of the major environmental crises one geographical spread, loss of life and property, has to contend of within the century. Flooding is defined displacement of people and socio-economic activities. as a large amount of water covering an area that was Pedro et al. (2019) also noted that river flooding is a usually dry (Emmanuel and Ojinnaka, 2015). Daniela et specific worldwide type of hazard responsible for al. (2018) reported that flood take place when the river considerable human and material losses. Apart from exceeds its storage capacity and the water excess over overflows of the rivers, floods maybe caused by failure of flows the banks and fills the adjacent low-lying lands. some hydraulic structures such as dams or sudden Mukoro et al. (2015) argued that flooding is considered release of huge amount of water as the case of 2012 the worst global hazard in terms of magnitude, occurrence, flood in Nigeria that hits Lokoja in Kogi State which was *Corresponding author. E-mail: [email protected]. Tel: 08035656394. Author(s) agree that this article remain permanently open access under the terms of the Creative Commons Attribution License 4.0 International License Ahuchaogu et al. 31 Figure 1. Scenarios created by flood in the study area. partly attributed to the release of water from Lagdo Dam only works well for basins that have long enough stream in Cameroon. It caused enormous damages to lives and flow records to warrant statistical analysis. The objective property in many states bordering river Niger Benue of frequency analysis of hydrologic data is to relate the basin and was considered as the worst event in the study magnitude of extreme events to their frequency of area and the entire Nigeria since over half a century. occurrence using probability distributions. The frequency Figure 1a and b shows scenarios created by 2012 flood or probability of a flood usually is described by assigning in the study area. However, Lin et al., (2019) reported a recurrence interval to the flood at each gauging station. that flooding is a common type of natural hazard caused This is accomplished by statistically evaluating long-term by intense rainfall. Knowledge of time of arrival of flood annual peak stream flows at that station. For example, a events improves safety and is important for a variety of 100-year flood-recurrence interval means that, in any planning. It allows precautionary measures to be taken given year, a flood of a specified stream flow magnitude and people to be warned so that they can be prepared in has a 1-in-100 chance of happening. Flood frequency advance for flooding conditions. Since man do a lot of analysis is generally taken to denote a statistical analysis activities on the flood plain, it is important that he predict of flood, their magnitudes and their frequencies flood and protect his environment in other not to be (occurrence rates in time). Whereas, structures like caught unawares. Though the occurrence of future flood culverts, storm drainage systems can be designed for cannot be prevented but the magnitude of impact can be relatively small floods (more frequent floods), structures reduced by developing opposite flood counter measures. such as dams, spillways, retention ponds, etc., which In the past, some of the structures used to control flood cause huge loss of life and property are designed for within the study area include levees, reservoir and relatively more severe floods which have relatively longer channel improvement. With the current situation, it has return periods. Therefore, to select a design flood, which become clear that these methods are in-adequate is not likely to occur during the life of a hydrologic therefore the need for a more reliable approach. As much structure, the design return period (T) should be much of the hydrologic data like flow rate (discharge) and greater than the estimated life of the structure, that is, the rainfall are statistical in nature, statistical methods are difference between the design return period and the most frequently needed to be used with the goal of fitting estimated life of the structure should be quite large a statistical distribution to the data (Prasuhn, 1992). For (Izinyon and Igbinoba, 2011). Because flood risk economic and efficient design of these measures, estimation is an inherently statistical problem, to derive discharge has to be estimated with some level of the risk of occurrence of any flood event, the frequency accuracy. Once accurate prediction of flow of certain distribution which can best describe the past magnitudes is made, an ideal solution can then be characteristics of the magnitude and the possibility of proffered by a hydraulic Engineer (Haan, 1977; Okonofua such flood must be known and this requires and Ogbeifun 2013). Hydrological data such as rate of determination of the most appropriate flood frequency flow and rainfall are used to design engineering structure model which can be fitted to the available historical data to mitigate flood as structures which are not design to or record. Whole group of models such as simple linear withstand major events might be destroyed by them regression, Gumbel (EV-1), Normal, Log normal, Pearson (Ibrahim and Isiguzo, 2009). Design flood is the Type III, Log-Pearson Type III, Weibull equation, etc., discharge selected for the design of a hydrological have been suggested in literature for the prediction of structure (Izinyon and Igbinoba, 2011). The time between extreme flood events however, this study adopted Log- floods of similar size is the return interval. Its procedure Pearson Type III probability distribution because it is 32 Int. J. Water Res. Environ. Eng. widely suggested in literature as the most suitable wet and dry seasons with a total annual rainfall between method. 1000 and 1500 mm. Mean annual temperature is about 27.7°C and a relative humidity of 30% in dry season and 70% in wet season. Average daily wind speed is 89.9 Significance of the study km/h.Wind speed is usually at its peak in March and April. The most important hydro-geological features are Whenever disasters of great magnitudes occur in a River Niger and the confluence of River Niger and Benue. country, efforts are usually made to prevent future The largest river in Nigeria (river Niger) flows through occurrences where possible, or at least minimize the Lokoja but it is under-utilized for transportation even impacts through various preventive programs and irrigation (Figure 2). mechanisms. Although Lokoja is regularly, under the influence of flash flood due to its location in the valley of the confluence of River Niger and Benue but the Statistical background unprecedented 2012 flood event has been describe is the worst in over half a century. Some parts of the area Pearson (1930) proposed a general formula that fits inundated for more than four days during the episode many probability distribution including the normal, beta with an average water height of 3 m. Some of the existing and gamma distribution. A form of the Pearson probability structures used to control flood in the study area are distribution called the Pearson Type III has three leaves, reservoir and channel improvement yet, the parameters that include the skew coefficient, as well as problems are unabated. Therefore, it has become the mean and standard deviation (Izinyon and Igbinoba, apparent that these measures are inadequate to handle 2011). The Log-Pearson Type III distribution is a the situation. However, for any method to be effective, statistical technique for modeling hydrological data.