Plotting Position Probability Fittings to Lagos Metropolitan Precipitation: Hydrological Tools for Hydraulic Structures Design in Flood Control

摘要

Hydraulic structures are generally designed based on the past records of concerned hydrologic events. Such events include temperature, rainfall, humidity, evaporation and a host of others. This paper focuses on the analysis of rainfall data of Lagos metropolis to synthesize a suitable rainfall intensity for a return period for the design of drainage channels within the metropolis. Rainfall data from 1960 to 2010 (fifty- one years ) , recorded on the basis of twenty four hours ,were collected from the office of the Nigerian Meteorological Agency, Oshodi. The data were well screened and converted to maximum annual hourly based on the assumption of uniform rainfall in intensity and duration after increasing by thirteen percent. Various graphical plotting formulae such as Hazen, Weibull , Blom, Gringorten, Tukey, California and Chegodayev were adopted to arrive at different best fitting equations. The fitted equations were used to determine various rainfall intensities with corresponding return periods. The rainfall intensities can be utilized with other design parameters required for hydraulic structures design.