Flood Predictions Using The Hydraulic Model

Usually, the analysis of water surface profile for any river or open channel requires a known discharge. In flood analysis, a discharge of certain Average Recurrence Interval is used to check the flooded stretches of a river. To compute a discharge of certain Average Recurrence Interval, the frequency analysis must be carried out. One of the primary objectives of the frequency analysis of hydrologic data is to determine the recurrence interval of a hydrologic event of a given magnitude. Hydrologic frequency analysis is the approach of using probability and statistical analysis to estimate future frequencies (probability of hydraulic events occurring) based upon information contained in hydrologic records. The U.S Water Resources Council (WRC) recommended that the log-Pearson Type III be used as a base method for flood flow frequency studies (Larry, 2001). The frequency factor equation for the log-Pearson Type III distribution is written in terms of discharge as

log QT = Q + KT(T,GS)Sy

where: QT = the discharge for the T-year return period
Q = mean
Sy = Standard deviation
KT = frequency factor (refer appendix C for the table of KT values for Pearson
Type III Distribution)
GS = skew of the log-transformed values

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