Flood Frequency Estimates in Southeastern Arizona

The effect of the October 1983 floods in southeastern Arizona, on a previously established generalized envelope for floods expected once in 100 years $\left(Q_{100}\right)\text{,}$ is studied. The design envelope is found to produce more conservative estimates of $Q_{100}$ than individual data sets find. The design envelope for $Q_{100}$ is revised to correct for some longer periods of record now available, and to be consistent with floods on a wider range of drainage area than previously considered. Additional design envelopes for floods expected once in 2 years $\left(Q_2\right)$ and once in 10 years $(Q_{10)}$ are prepared, and the three envelopes are used to provide conservative estimates of flood frequencies on ungaged watersheds in southeastern Arizona with drainage areas between $0.01{\mathrm{km}}^2$ and $10\text{,}000{\mathrm{km}}^2\text{.}$ A procedure is presented for developing regional flood frequency estimates that could be used in geographically and climatically homogeneous areas.