Development of Intensity Duration Frequency (IDF) Curve for Parts of Eastern Catchments using Modern Arcview GIS Model

Abstract

The hydraulic and structural design of control structures have failed in many years due to lack of geodetic and reliable hydrologic analysis of rainfall and discharge data in some catchments. Hydrologists are often faced with the task of using a limited number of quantitative observations, together with a conceptual understanding of the operation of processes involved in the movement of water through the hydrological cycle, to estimate the occurrence of water at various locations. This is usually done with the assistance of hydrological models which not only have to consider the precipitation and runoff at a certain point, but also other variables such as topography, vegetation cover, rooting characteristics, etc. The Intensity Duration Frequency (IDF) relationship is a mathematical relationship between the rainfall intensity, the duration and the return period. This relationship is determined through statistical analysis of samples of records at proper meteorological stations. This are typically performed based on specified design storms derived from the rainfall intensity-duration-frequency (IDF) estimates and an assumed temporal distribution of rainfall. Use of inappropriate data or design storms could lead to malfunctions of the infrastructure systems: over-estimation may result in costly over design, or under-estimation may be associated to risk of human safety.The hydrologic design of flood storage structures is done by computing the discharge rate for 2, 5, 10, 25, 50 or 100 years return period, which indicate that the heaviest rain occurred once in either 2, 5, 10, 25, 50 or 100 years period respectively as the case may be. The development of IDF curve is of paramount importance in the determination of design discharge. This paper analysed rainfall data from four different gauged rainfall stations that are homogenous and applied to ArcView GIS model to generate regional rainfall intensity (RRI) map using the “inverse distance weighting method” for the interpolation of the stations values.