Practical Method of Estimating Peak Flow

A practical method is suggested for estimating the peak flow. The variables used are the mean daily flows of three consecutive days with the maximum mean daily flow occupying the middle position. A parameter, designated as base factor K, has a governing influence on the estimated peak. Its value lies between zero and two. The predicting formula used in this study assumes the K value equal to one. The method was applied to streams in Ontario. A total of 387 stations equipped with recording gages were used. The drainage areas of the basins varied from less than $1{\mathrm{km}}^2$ to more than $100\text{,}000{\mathrm{km}}^2\text{.}$ The number of instantaneous peak data available was 3,946 in the period of record ending in 1979. About 57% of the predicted peaks lie within $\pm 10\%\text{,}$ and 79% lie within $\pm 20\%$ of the actual values. About 62% of the peaks were overpredicted. The parameter K must be estimated for rainfall floods occurring on small streams. Its value will generally be less than one for such cases. Methods are suggested for its estimation.