Flood Metrics and Flood Series Effect in Akpoha and Ebonyi Rivers South Eastern Nigeria

This work evaluated the annual Flood metrics and flood series effect in Akpoha and Ebonyi rivers. It adopted flood metrics of the rivers for four seasons to determine the flood series within the period of study. This assessment tried to determine the flood series in the respective seasons within the period of study. The evaluation also provided information on the annual flooding in the affected floodplains given the volume of flood water available at each point. Akpoha and Ebonyi rivers were sampled at different points. The design of 4×4 factorial was applied to determine the relationship between sample points and parameters for control, 2014 and 2015 and 2016 using analysis of variance for Completely Randomized Design. Mean values evaluated for significant differences using Fisher’s Least Significant Differences at P < 0.01.T-test was used for confirmation. The rivers sampled at four points, a1, a2, a3, a4 Akpoha as well b1, b2, b3, b4.Ebonyi. The main factors determined were discharge, flow velocity, width and depth. Results showed that the factors were highly statistically significant at 1% level and the confirmatory test via FLSD also agreed to that. Results of evaluation of flood series a1 and a2 showed that the highest No of 1-day maximum flood of 743.01 m3/s, 584.10 m3/s and 748.87 m3/s, 673.91 m3/s were recorded in 2015,P- probability of return are 5.88% and 11.76%.T- the recurrent intervals are 17 and 8.5 respectively.536 m3/s, 513 m3/s,423.33 m3/s and 322.83 m3/s, 320.39 m3/s, 274.10 m3/s were observed at a3,a4, a5, and b3,b4,b5 in 2016  which also showed that the probability of occurrences are 17.54%, 23.26% and 29.41%. Year of occurrences 5.7, 4.3 and 3.4 respectively. The 1-day maximum flood of 26.63 m3/s and 8.14 m3/s in the control (2013). 62.85 m3/s and 56.35 m3/s recorded in 2014 showed 1.3 and 1.9 recurrent intervals and 76.92%, 52.63% probability of return. The discharge result showed that the recurrent interval for control < 2014 < 2015 < 2016 except at a1 a2.and b1, b2, 2016 < 2015 at a8 and b8. The record also showed that the probability of return for the control >2014 > 2015 > 2016.  The 1-day maximum flood reflected the amount of water discharged by the water bodies at that point in the control, 2014 and 2015. The control indicated that a very low amount 23.22 m3/s and 6.12 m3/s were observed initially and that large amount of 743.01 m3/s and 748. 87 m3/s were observed in 2016 while medium amount of 62.85 m3/s and 56.35 m3/s were recorded in 2014. The results were recommended to individuals living in floodplains to enable them exploit water benefits from the areas and also take note of the flood series within the floodplains.

Keywords: Floodplain, Flood Series, 1- day Maximum Flood, Recurrent interval, probability of flood return.