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 (Q100), is studied. The design envelope is found to produce more conservative estimates of Q100 than individual data sets find. The design envelope for Q100 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 (Q2) and once in 10 years (Q10) 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 0.01km2 and 10,000km2. A procedure is presented for developing regional flood frequency estimates that could be used in geographically and climatically homogeneous areas.