attention and research on the IDF relationship: Hershfield (1961) developed various rainfall contour maps to provide the design rain depths for various return periods and durations. Bell (1969) proposed a generalized IDF formula using the one hour, 10 years rainfall depths; P110, as an index. Chen (1983) further developed a generalized IDF formula for any location in the United States using three base rainfall depths: P110, P2410, P1100, which describe the geographical variation of rainfall. Kouthyari and Garde (1992) presented a relationship between rainfall intensity and P242 for India. Koutsoyiannis et al. (1998) cited that the IDF relationship is a mathematical relationship between the rainfall intensity i, the duration d, and the return period T (or, equivalently, the annual frequency of exceedance, typically referred to as 'frequency' only). This paper proposes the approach to the formulation and construction of IDF curves using
data form recording station by using empirical equations, and comparison the equations, choosing what equation can be used in the monsoon area of Vietnam. Normally, rainfall intensity-durationfrequency relationship is derived from the point rain gauges, the network of daily rainfall recording rain gauges in Vietnam has higher density than short duration (hourly or minutes) rain gauges . The regional IDF formula parameters are generated for ungauged areas to estimate rainfall intensity for various return period and rainfall duration. The method proposed in this study is reasonably applicable to ungauged rainfall locations, which is concluded from the verification of additional rain gauges. More specifically, this research is to study the generalized IDF formula using some base rainfall depth and base return period. Two main procedures are presented in this study. The first produces the set of IDF curves at 7 stations by using empirical functions. The second produces a generalized IDF equation for location area. The paper is organized in five sections, the first being this introduction. In Section 2 we give the traditional methods to establish IDF curves using empirical equations and regional parameters of equations. Section 3 deals with generalization rainfall intensity duration frequency formulas. Section 4 demonstrates the proposed procedures with applications using real world data (Red River Delta in Vietnam). Conclusions are drawn in Section 5.

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